Photoisomerization of geranial and nerolaldehyde

Abstract

The present invention relates to a process comprising isomerizing nerolaldehyde of formula (II) to geranial of formula (I), or isomerizing geranial to nerolaldehyde, characterized in that (a) isomerization is accomplished by irradiation with light. The method according to the invention makes it possible to very efficiently convert undesired isomers, which are unavoidable by-products generated during the production of nerolaldehyde and / or geranial, into desired isomers, the economic benefits of the process for producing desired isomers (in high yields by avoiding cost-intensive distillation and avoiding possible by-products) are thus greatly improved.

Description

[0001] This invention relates to a method comprising making a formula (II) The isomerization of nerol to the formula (I) Geranialdehyde, or the isomerization of geranialdehyde to neraldehyde, characterized in that (a) the isomerization is accomplished by light irradiation. The method according to the invention enables the very efficient conversion of undesirable isomers (which are unavoidable byproducts generated during the production of neraldehyde and / or geranialdehyde) into desired isomers, thereby greatly improving the economic efficiency of methods for producing desired isomers (in high yields by consuming as little energy as possible and avoiding possible byproducts). Background Technology

[0002] CN 112142583A relates to a method for using the formula (I) Preparative formula of geranialdehyde (II) The method for nerol, characterized in that geraniol is reacted with carbon monoxide and by reacting triethylaluminum with the formula (III) bis-diarylphenol ligands (where R 1 R 2 R 3 and R 4 They were selected independently from C6-C. 15 Aryl, R 5 It is isomerized to neraldehyde in the presence of a catalyst obtained from the reaction of hydrogen, C1-C6 alkyl and C1-C6 perfluoroalkyl.

[0003] CN 107879914A relates to a method for preparing nerol by efficiently distilling citral, comprising the steps of: distilling and separating citral containing two isomers, nerol and geranialdehyde, through a distillation column, and obtaining the nerol product at the top of the distillation column, wherein iodine and phosphorus catalytic active centers are loaded onto the packing of the stripping section of the distillation column, such that the material flowing through the bottom of the column and rich in geranialdehyde is catalytically converted into a material with an increased proportion of nerol.

[0004] CN 112125782A relates to a method for preparing high-purity nerol and geranialdehyde by hydrogenating citral, characterized by comprising the following steps: selectively catalytically hydrogenating nerol in citral using a novel transition metal composite catalyst to obtain nerol, without catalytically reacting geranialdehyde, and separating the reaction products by distillation to obtain high-purity nerol and geranialdehyde; wherein the novel transition metal composite catalyst comprises a transition metal compound and a chiral spirobisoxazoline ligand having a spirodihydroindene skeleton.

[0005] RU 2579122 relates to a method for obtaining geranialdehyde from a mixture of isomers of geranialdehyde and neraldehyde (citral) by conversion of citral in the presence of an acid catalyst, preferably montmorillonite clay, wherein the separation of geranialdehyde from the reaction mixture can be achieved by column chromatography or by distillation under reduced pressure.

[0006] Wout AM Wolken et al., J. Agric. Food Chem., 48(2000) 5401-5405, reported the deacetylation of citral (the main aromatic component) catalyzed by amino acids or proteins under alkaline conditions, yielding methylheptenone and acetaldehyde. 3-Hydroxycitronellal is an intermediate in this reaction. Amino acids also catalyze the cis-trans isomerization of pure isomers of citral, geranialdehyde, and neraldehyde. The glycine-catalyzed isomerization of geranialdehyde is a relatively rapid process (Figure 1A). Equilibrium was reached after 80 min with 60% geranialdehyde and 40% neraldehyde. The same equilibrium was reached starting with neraldehyde (Figure 1B).

[0007] OS Bokareva, Computational and Theoretical Chemistry, 1149 (2019) 8-16, discusses the quantum chemical study of the structure and conformational dynamics of trans- and cis-crotonaldehyde in excited electronic states.

[0008] Jens Holz et al., Adv. Synth. Catal. 2017, 359, 4379-4387, describe the highly chemoselective hydrogenation of neraldehyde to citronellol. The reaction was carried out using a homogeneous rhodium complex. The desired high activity and chemoselectivity of citronellol were achieved at 0.1 MPa and room temperature. Under the same conditions, geranialdehyde was also reduced to citronellol.

[0009] CN 116474824A relates to a catalyst for isomerizing nerol to geranialdehyde, characterized in that: the catalyst is one or more of citric acid, tartaric acid, amino acids and malic acid; and relates to a method for increasing the geranialdehyde content in citral, comprising adding the catalyst to citral.

[0010] RC Cookson et al., Tetrahedron 19 (1963), pp. 1995–2007, describe the cyclization of citral to 2-isopropenyl-5-methylcyclopentane-formaldehyde using UV irradiation with a medium-pressure mercury arc lamp. A footnote* on page 1 notes that the samples used were a 1:1 mixture of cis and trans isomers, and that interconversion between the geometric isomers (of citral) may be faster than cyclization.

[0011] WL Dilling, Chemical Reviews (1966), pp. 373-393, deals with intramolecular photochemical cycloaddition reactions of nonconjugated alkenes. Irradiation in cyclohexane or ethanol produces cis- and trans-citral cycloaddition products XVIII and hydrogen-migrating products XIX (p. 376, column 2, paragraph 1).

[0012] Yuko Iwanami et al., Journal of Agricultural and Food Chemistry, 45 (1997), pp. 463-466, discuss the changes in lemon flavor components in aqueous solutions during UV irradiation. Citral decreased rapidly with ZE isomerization under light irradiation, and new peaks appeared, such as peaks I, II, and III (p. 464, column 2, paragraph 6 and p. 465, column 1, paragraph 2, and Figure 1). Furthermore, citral in ethanol irradiated with UV light under nitrogen yielded products 3 to 12, as shown in Figure 2.

[0013] The aim is to provide a method for efficiently obtaining nerol or geranialdehyde.

[0014] Another objective of this invention is to convert undesirable isomers (which are unavoidable byproducts generated during the production of nerol and geraniol) into desired isomers very efficiently, thereby greatly improving the economics of methods for producing desired isomers (in high yields by avoiding cost-intensive distillation and potential byproducts).

[0015] Surprisingly, it was found that the above objectives can be achieved using the method according to the present invention.

[0016] Accordingly, the present invention relates to a method comprising making a formula (II; Citral B (cis form)) isomerized with nerol to form (I; Citral A (trans form)) geranialdehyde, or isomerization of geranialdehyde to nerol, characterized in that (a) the isomerization is accomplished by light irradiation.

[0017] In other words, the present invention relates to a method for isomerizing neraldehyde of formula (II; citral B (cis form)) to geranialdehyde of formula (I; citral A (trans form)) or isomerizing geranialdehyde to neraldehyde, characterized in that (a) the isomerization is accomplished by irradiation with light.

[0018] In other words, the present invention relates to the production of desired isomers (nerol or geranialdehyde), comprising isomerizing nerol of formula (II; citral B (cis form)) to geranialdehyde of formula (I; citral A (trans form)) or isomerizing geranialdehyde to nerol, characterized in that (a) the isomerization is accomplished by light irradiation.

[0019] In a preferred embodiment, the method is a method for producing a desired isomer, particularly neraldehyde or geranialdehyde (optionally included in a mixture comprising neraldehyde and geranialdehyde).

[0020] In other words, the method of the present invention can be a method for preparing enriched or pure neraldehyde and / or geranialdehyde.

[0021] It will be understood that the produced nerol can be pure nerol or enriched nerol, i.e., nerol contained in a mixture that further comprises geranialdehyde and optionally one or more other components, having a higher nerol content than the mixture prior to isomerization in (step a). It will also be understood that the produced geranialdehyde can be pure geranialdehyde or enriched geranialdehyde, i.e., geranialdehyde contained in a mixture that further comprises nerol and optionally one or more other components, having a higher geranialdehyde content than the mixture prior to isomerization in (step a).

[0022] In a preferred embodiment, the illumination is performed using monochromatic light.

[0023] In a preferred embodiment, geranialdehyde is irradiated with monochromatic light in step a), or nerol is irradiated with monochromatic light in step a).

[0024] It will be understood that irradiation of geraniol does not preclude the accompanying irradiation of nerol, and vice versa, especially when irradiation is performed on a mixture consisting of or containing both nerol and geraniol. Irradiation of nerol can be pure nerol or on a mixture consisting of or containing both nerol and geraniol, particularly on enriched nerol (i.e., a mixture containing a higher content of nerol). One or more irradiations can result in a changed, preferably more desirable, nerol:geraniol ratio.

[0025] In a preferred embodiment, the method of the present invention is used to increase the nerol content in a composition, particularly a mixture comprising geranialdehyde and nerol, and includes the following steps:

[0026] a) Isomerize enriched or pure geranialdehyde into a mixture of neraldehyde and geranialdehyde by irradiation with light.

[0027] In a preferred embodiment, the method of the present invention is used to increase the geranialdehyde content in a composition, particularly a mixture comprising geranialdehyde and neraldehyde, and includes the following steps:

[0028] a) Isomerization of enriched or pure neraldehyde into a mixture of neraldehyde and geranialdehyde by light irradiation.

[0029] In a particularly preferred embodiment of the invention (wherein a sensitizer is present in step a), monochromatic light is the total radiation emitted in the range of 350 nm to 490 nm, comprising at least 90% and at most 100% of its power. Specifically, at least 90% and at most 100% of the radiant flux of the monochromatic light is emitted in the range of 350 nm to 490 nm. The single-peak emission spectrum preferably exhibits a half-width of no more than + / - 100 nm, preferably no more than + / - 60 nm, such as + / - 10 to + / - 30 nm, relative to the wavelength of the emission peak.

[0030] In another particularly preferred embodiment of the invention (where no sensitizer is present in step a), monochromatic light is the total radiation emitted in the range of 300 nm to 420 nm, comprising at least 90% and at most 100% of its power. Specifically, at least 90% and at most 100% of the radiant flux of the monochromatic light is emitted in the range of 300 nm to 420 nm. Its single-peak emission spectrum preferably exhibits a half-width of no more than + / - 100 nm, preferably no more than + / - 60 nm, such as + / - 10 to + / - 30 nm, relative to the wavelength of the emission peak.

[0031] The defined half-width provides a highly structured lighting profile, which results in increased nerol / geraniol yield.

[0032] The method according to the invention enables the highly efficient conversion of undesirable isomers (which are unavoidable byproducts generated during the production of nerol and / or geraniol) into desired isomers, thereby greatly improving the economic efficiency of methods for producing desired isomers (in high yields by avoiding cost-intensive distillation and potential byproducts).

[0033] Furthermore, the method of the present invention is commercially attractive because it enables the efficient, demand-driven production of nerol or geraniol, and thus provides greater flexibility in the production of aromatic chemicals.

[0034] This invention enables the efficient production of neraldehyde or geranialdehyde.

[0035] Therefore, in the first embodiment, the present invention relates to...

[0036] N.1 A method for preparing enriched or pure neraldehyde, comprising the following steps

[0037] a) Isomerization of enriched or pure geranialdehyde into a mixture of neraldehyde and geranialdehyde by light irradiation.

[0038] b) Separating, especially (continuously) separating, the mixture containing geranialdehyde and neraldehyde obtained in step a) to obtain the product, enriched or pure neraldehyde and enriched or pure geranialdehyde; and

[0039] c) Optionally, the enriched or purified geranialdehyde obtained in step b) is recycled to step a).

[0040] N.2 The method according to Example N.1 further includes, as step 0), providing enriched or pure geranialdehyde by distillation separation of a mixture containing geranialdehyde and nerol.

[0041] N.3 The method according to Example N.1 or N.2, wherein, in step a), the solution of geranialdehyde in the solvent is irradiated with light.

[0042] N.4 The method according to Example N.3, wherein the solvent is selected from water, dichloromethane, trichloromethane, tetrachloromethane, CS2, C1-C4 alcohols, chlorobenzene, fluorobenzene, trifluoromethylbenzene, acetonitrile, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), ethyl acetate, acetone, and mixtures thereof.

[0043] N.5 The method according to any one of Examples N.1 to N.4, wherein, in step a), the geranialdehyde is irradiated with light in the presence of a sensitizer.

[0044] N.6 The method according to Example G.5, wherein the sensitizer is selected from [Ir(dF(CF3)ppy)2(bpy)]PF6, (Ir[dF(CF3)ppy]2(dtbbpy))PF6, (Ir[dF(CF3)ppy]2(dtbpy))PF6, (Ir[dF(Me)ppy]2(dtbbpy))PF6, [Ir(dtbbpy)(ppy)2]PF6, Ir(ppy)3, Ru(bpy)3Cl3, [Ru(bpy)... 3] (PF6)2, Benzophenone, Thioxanthone-9-one, Mischelone, Tetramethoxy-anthraphenthone, Diacetyl-4,5-bis(carbazole-9-yl)-1,2-dicyanophenylene (2CzPN), 3,4,5,6-Tetra(9H-carbazole-9-yl)phthalonitrile (4CzPN), 1,2,3,5-Tetra(carbazole-9-yl)-4,6-dicyanophenylene (4CzIPN), 4-Methoxythoxanone (4-MeOTX), 3-Methoxythoxanone (3-MeOTX), 2-Methoxythoxanone (2-MeOTX), 3-Fluorothoxanone ( 3-FTX), 2-fluorothioxanthione (2-FTX), 3,6-dimethoxythioxanthione (3,3'-MeOTX), 3,6-difluorothioxanthione (3,3'-FTX), 2-methoxy,7-fluorothioxanthione (2-F,2'-MeOTX), 2,7-dimethoxythioxanthione (2,2'-MeOTX), and 9-trimethyl-10-methylacridinium tetrafluoroborate, trimethyl-10-methylacridinium perchlorate, eosin Y, eosin B, 9,10-diphenylanthracene, 9,10-dicyanoanthracene, Rose Bengal, and mixtures thereof.

[0045] N.7 The method according to Example N.5 or N.6, wherein, in step a), the geranialdehyde is irradiated with monochromatic light in the wavelength range of 350 to 490 nm.

[0046] N.8 The method according to Example N.1 or N.2, wherein, in step a), the geranialdehyde is irradiated with light in a pure form, i.e., without solvent and sensitizer.

[0047] N.9 The method according to Example N.8, wherein, in step a), the geranialdehyde is irradiated with monochromatic light in the wavelength range of 300 to 420 nm.

[0048] N.10 The method according to any one of the foregoing embodiments, wherein step a) is performed in a temperature range of -20°C to 100°C.

[0049] N.11 The method according to any one of the foregoing embodiments, wherein step a) is performed in a pressure range from 1 mbar to 20 bar.

[0050] N.12 The method according to any one of the foregoing embodiments, wherein step a) is carried out in a continuously stirred reactor, in a pumping loop, or in a continuous flow reactor.

[0051] N.13 The method according to any one of the foregoing embodiments, wherein the light irradiation is accomplished by using at least one LED (light-emitting diode) or laser.

[0052] N.14 The method according to any one of the foregoing embodiments is a method for producing menthol and includes additional steps d.1) to g.1):

[0053] d.1) Catalytically hydrogenating nerol obtained by the method of the present invention (e.g., according to any one of claims 1-3, 6-16, 18-23), preferably nerol obtained in any one of steps 0), a), and / or b) (e.g., 0) and / or b), or a) and / or b)) to obtain citronellol.

[0054] e.1) Cyclization of citronellol in the presence of an acidic catalyst to obtain isopreneol.

[0055] f.1) Optionally purify isomenthol, preferably by crystallization, and

[0056] g.1) Catalytically hydrogenate isomenthol to obtain menthol.

[0057] N.15 The method according to embodiment N.14 includes additional steps d.2) to g.2):

[0058] d.2) Asymmetric catalytic hydrogenation of nerol obtained by the method of the present invention (e.g., according to any one of claims 1-3, 6-16, 18-23), preferably obtained in steps 0), a), and / or b) (e.g., 0) and / or b), or a) and / or b)), to obtain optically active citronellol.

[0059] e.2) Cyclize optically active citronellol in the presence of an acidic catalyst to obtain optically active isopreneol.

[0060] f.2) Optionally purify optically active isoprene, preferably by crystallization, and

[0061] g.2) Catalytically hydrogenate optically active isomenthol to obtain optically active menthol.

[0062] Compared to the teachings of existing technologies, the photochemical isomerization of geranialdehyde advantageously produces a mixture of nerol and geranialdehyde, wherein nerol is present in an amount greater than 50% of geranialdehyde.

[0063] In the second embodiment, the present invention relates to...

[0064] G.1 A method for preparing enriched or pure geranialdehyde, comprising the following steps

[0065] a) Isomerization of enriched or pure neraldehyde into a mixture of neraldehyde and geranialdehyde by light irradiation;

[0066] b) Separation, especially (continuous) distillation, of the mixture containing geranialdehyde and neraldehyde obtained in step a) to obtain the product, enriched or pure geranialdehyde and enriched or pure neraldehyde; and

[0067] c) Optionally, the enriched or purified neraldehyde obtained in step b) is recycled to step a).

[0068] G.2 The method according to Example G.1 further includes, as step 0), providing enriched or pure neraldehyde by distillation separation of a mixture containing geranialdehyde and neraldehyde.

[0069] G.3 The method according to Example G.1 or G.2, wherein in step a), the solution of nerol in the solvent is irradiated with light.

[0070] G.4 The method according to Example G.3, wherein the solvent is selected from water, dichloromethane, trichloromethane, tetrachloromethane, CS2, C1-C4 alcohols, chlorobenzene, fluorobenzene, trifluoromethylbenzene, acetonitrile, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), ethyl acetate, acetone, and mixtures thereof.

[0071] G.5 The method according to any one of Examples G.1 to G.4, wherein, in step a), the nerol is irradiated with light in the presence of a sensitizer.

[0072] G.6 The method according to Example G.5, wherein the sensitizer is selected from [Ir(dF(CF3)ppy)2(bpy)]PF6, (Ir[dF(CF3)ppy]2(dtbbpy))PF6, (Ir[dF(CF3)ppy]2(dtbpy))PF6, (Ir[dF(Me)ppy]2(dtbbpy))PF6, [Ir(dtbbpy)(ppy)2]PF6, Ir(ppy)3, Ru(bpy)3Cl3, [Ru(bpy)... 3](PF6)2, Benzophenone, Thioxanthone-9-one, Mischelone, Tetramethoxy-anthraphenthone, Diacetyl-4,5-bis(carbazole-9-yl)-1,2-dicyanophenylene (2CzPN), 3,4,5,6-Tetra(9H-carbazole-9-yl)phthalonitrile (4CzPN), 1,2,3,5-Tetra(carbazole-9-yl)-4,6-dicyanophenylene (4CzIPN), 4-Methoxythoxanone (4-MeOTX), 3-Methoxythoxanone (3-MeOTX), 2-Methoxythoxanone (2-MeOTX), 3-Fluorothoxanone ( 3-FTX), 2-fluorothioxanthione (2-FTX), 3,6-dimethoxythioxanthione (3,3'-MeOTX), 3,6-difluorothioxanthione (3,3'-FTX), 2-methoxy,7-fluorothioxanthione (2-F,2'-MeOTX), 2,7-dimethoxythioxanthione (2,2'-MeOTX), and 9-trimethyl-10-methylacridinium tetrafluoroborate, trimethyl-10-methylacridinium perchlorate, eosin Y, eosin B, 9,10-diphenylanthracene, 9,10-dicyanoanthracene, Rose Bengal, and mixtures thereof.

[0073] G.7 The method according to Example G.5 or G.6, wherein, in step a), the nerol is irradiated with monochromatic light in the wavelength range of 350 to 490 nm.

[0074] G.8 The method according to Example G.7 or G.8, wherein in step a), neraldehyde is irradiated with light in its pure form, i.e., without solvent and sensitizer.

[0075] G.9 The method according to Example G.8, wherein in step a), the nerol is irradiated with monochromatic light in the wavelength range of 300 to 420 nm.

[0076] G.10 ​​The method according to any one of the foregoing embodiments, wherein step a) is performed in a temperature range of -20°C to 100°C.

[0077] G.11 The method according to any one of the foregoing embodiments, wherein step a) is performed in a pressure range from 1 mbar to 20 bar.

[0078] G.12 The method according to any one of the foregoing embodiments, wherein step a) is carried out in a continuously stirred reactor, in a pumping loop, or in a continuous flow reactor.

[0079] G.13 The method according to any one of the foregoing embodiments, wherein the light irradiation is accomplished by using at least one LED (light-emitting diode) or laser.

[0080] G.14 The method according to any one of the foregoing embodiments is a method for producing linalool and includes additional steps d') and e'):

[0081] d') Catalytically hydrogenate geranialdehyde and / or neraldehyde obtained by the method of the present invention, preferably geranialdehyde obtained by the method of the present invention, especially geranialdehyde obtained in any one of steps 0), a), and / or b) (e.g., 0) and / or b), or a) and / or b)), particularly catalytically hydrogenate geranialdehyde obtained in any one of steps 0), a), and / or b) (e.g., 0) and / or b), or a) and / or b)) in the presence of a supported ruthenium, rhodium, osmium, iridium, or platinum catalyst, preferably a ruthenium catalyst supported on carbon black; to obtain geraniol; and

[0082] e') Isomerize geraniol in the presence of a catalyst, especially a tungsten catalyst, and very especially a dioxotungsten (VI) complex, to obtain linalool.

[0083] In a first preferred embodiment, the present invention relates to a method for preparing enriched or pure neraldehyde, comprising the following steps:

[0084] a) Isomerize enriched or pure geranialdehyde into a mixture of neraldehyde and geranialdehyde by irradiation with light.

[0085] Enriched or pure geranialdehyde is preferably provided by separating a mixture comprising geranialdehyde and nerol. Enriched or pure geranialdehyde is preferably provided by distillation separation of a mixture comprising geranialdehyde and nerol. Optionally, the separation can be partial or complete, in other words, it can include obtaining pure geranialdehyde and / or pure nerol, and / or a mixture of nerol and geranialdehyde, or a mixture thereof, having a desired nerol:geranialdehyde mass ratio that may differ from that of the separation feed.

[0086] Distillation techniques for partially or completely separating neraldehyde and geranialdehyde from each other (in other words, enriching neraldehyde and / or geranialdehyde in a fraction) can be carried out by any means suitable for that purpose. Examples of suitable distillation procedures are taught in WO 2009 / 068444.

[0087] Therefore, the present invention relates to a method for preparing enriched or pure neraldehyde, comprising the following steps:

[0088] 0) The mixture containing geranialdehyde and neraldehyde is distilled to obtain enriched or pure geranialdehyde and neraldehyde.

[0089] a) Isomerize the enriched or pure geranialdehyde obtained in step 0) into a mixture of nerol and geranialdehyde by irradiation with light.

[0090] Preferably, the mixture containing geranialdehyde and neraldehyde obtained in step a) is distilled to obtain enriched or pure neraldehyde and enriched or pure geranialdehyde, which is then recycled to step a). The distillation separation is preferably a continuous distillation separation.

[0091] Therefore, the present invention relates to a method for preparing enriched or pure neraldehyde, comprising (preferably continuously) the following steps.

[0092] a) Isomerization of enriched or pure geranialdehyde into a mixture of neraldehyde and geranialdehyde by light irradiation.

[0093] b) Continuous distillation to separate the mixture containing geranialdehyde and neraldehyde obtained in step a) to obtain the product, enriched or pure neraldehyde and enriched or pure geranialdehyde; and

[0094] c) Optionally, the enriched or purified geranialdehyde obtained in step b) is recycled to step a).

[0095] As used herein, the terms "product, enriched or pure neraldehyde and enriched or pure geranialdehyde" can be understood as at least two separate streams: a first stream of enriched or pure neraldehyde and a second stream of enriched or pure geranialdehyde. In this context, the first stream of enriched or pure neraldehyde can preferably be considered the desired product, and the second product can be considered a byproduct that can optionally be recycled (e.g., in step c).

[0096] As used herein, the terms "product, enriched or pure geranialdehyde and enriched or pure neraldehyde" can be understood as at least two separate streams: a first stream of enriched or pure neraldehyde and a second stream of enriched or pure geranialdehyde. In this context, the first stream of enriched or pure geranialdehyde can preferably be considered the desired product, and the second product can be considered a byproduct that can optionally be recycled (e.g., in step c).

[0097] In a particularly preferred embodiment, the present invention relates to a method for preparing enriched or pure neraldehyde, comprising (preferably continuously) the following steps:

[0098] 0) The mixture containing geranialdehyde and neraldehyde is distilled to obtain enriched or pure geranialdehyde and neraldehyde.

[0099] a) Isomerize the enriched or pure geranialdehyde obtained in step 0) into a mixture of nerol and geranialdehyde by irradiation with light.

[0100] b) Continuous distillation to separate the mixture containing geranialdehyde and neraldehyde obtained in step a) to obtain the product, enriched or pure neraldehyde and enriched or pure geranialdehyde; and

[0101] c) Optionally, the enriched or purified geranialdehyde obtained in step b) is recycled to step a).

[0102] In a second preferred embodiment, the present invention relates to a method for preparing enriched or pure geranialdehyde, comprising the following steps:

[0103] a) Isomerization of enriched or pure neraldehyde into a mixture of neraldehyde and geranialdehyde by light irradiation.

[0104] Enriched or pure geranialdehyde is preferably provided by distillation to separate a mixture containing geranialdehyde and neraldehyde.

[0105] Accordingly, the present invention relates to a method for preparing enriched or pure geranialdehyde, comprising the following steps:

[0106] 0) The mixture containing geranialdehyde and neraldehyde is distilled to obtain enriched or pure geranialdehyde and neraldehyde.

[0107] a) Isomerize the enriched or pure neraldehyde obtained in step 0) into a mixture of neraldehyde and geranialdehyde by irradiation with light.

[0108] Preferably, the mixture containing geranialdehyde and neraldehyde obtained in step a) is distilled to obtain enriched or pure geranialdehyde and enriched or pure neraldehyde, which are then recycled to step a). The distillation separation is preferably a continuous distillation separation.

[0109] Therefore, the present invention relates to a method for preparing enriched or pure geranialdehyde, comprising (preferably continuously) the following steps.

[0110] a) Isomerization of enriched or pure neraldehyde into a mixture of neraldehyde and geranialdehyde by light irradiation;

[0111] b) Distilling the mixture containing geranialdehyde and neraldehyde obtained in step a) to obtain the product, enriched or pure geranialdehyde and enriched or pure neraldehyde; and

[0112] c) Optionally, the enriched or purified neraldehyde obtained in step b) is recycled to step a).

[0113] In a particularly preferred embodiment, the present invention relates to a method for preparing enriched or pure geranialdehyde, comprising (preferably continuously) the following steps:

[0114] 0) The mixture containing geranialdehyde and neraldehyde is distilled to obtain enriched or pure geranialdehyde and neraldehyde.

[0115] a) Isomerize the enriched or pure neraldehyde obtained in step 0) into a mixture of neraldehyde and geranialdehyde by irradiation with light.

[0116] b) Distilling the mixture containing geranialdehyde and neraldehyde obtained in step a) to obtain the product, enriched or pure geranialdehyde and enriched or pure neraldehyde; and

[0117] c) Optionally, the enriched or purified neraldehyde obtained in step b) is recycled to step a).

[0118] Step 0)

[0119] The method of the present invention preferably further includes, as step 0), distillation separation of a mixture containing geranialdehyde and nerol to obtain enriched or pure geranialdehyde or nerol.

[0120] The suitable feed material in step 0) is a mixture of substances containing neraldehyde and geranialdehyde, preferably those mainly composed of the double bond isomers neraldehyde and geranialdehyde. Among these, the following mixtures are preferred: containing at least 90% to 100% by weight, particularly preferably at least 95% to 98% by weight (in each case based on the total amount of the respective mixture) of geranialdehyde and neraldehyde, or consisting of them in a specified fraction, and may also contain additional components, such as isomers, byproducts, or impurities, to a low extent (i.e., at a fraction of up to 10% by weight, preferably up to 5% by weight) (in each case based on the total amount of the respective mixture). A preferred feedstock is synthetically produced citral, particularly those already obtained by thermally decomposing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal, eliminating isopentenol to give cis / trans-isopentenyl (3-methylbutadienyl) ether, rearranging it via the Claisen rearrangement to give 2,4,4-trimethyl-3-formyl-1,5-hexadiene, and subsequently via the Cope rearrangement, as described, for example, in EP992477 and European Patent Application No. 23177047.0. This typically comprises about 45% to about 55% neraldehyde by weight and about 55% to about 45% and about 1% to 5% by weight of other compounds and / or impurities.

[0121] The method according to the invention includes the above-described method for producing citral, which begins with 3-methyl-2-buten-1-aldehyde diisopentenyl acetal as an additional inserting step.

[0122] The mixture of substances used in step 0) preferably consists of 30% to 70%, preferably 40% to 60% by weight of nerol, 70% to 30%, preferably 60% to 40% by weight of geraniol, and 0% to 5% by weight of other components, wherein the total percentages reach 100% by weight.

[0123] In a preferred embodiment, the method according to the invention includes, as step 0), distillation to separate a mixture containing geranialdehyde and nerol to obtain enriched or pure geranialdehyde or nerol. See WO 2009 / 068444.

[0124] Furthermore, the distillation separation of mixtures containing geranialdehyde and neraldehyde can advantageously be carried out by means of interconnecting partitioned columns or heat-coupled columns. In this manner, neraldehyde is obtained, in particular, by distillation separation of mixtures containing geranialdehyde and neraldehyde in pure or enriched form.

[0125] In a preferred embodiment, a continuous method is inserted for producing nerol in pure or enriched form by distilling off nerol from a mixture of substances containing nerol and geraniol. The distillation is carried out at an absolute operating pressure of 5 to 200 mbar in a partitioned column or an interconnection of two thermally coupled distillation columns having 80 to 200 theoretical plates and one or more side-feed points.

[0126] Distillation removal is typically carried out by separating the mixture of substances containing nerol and geraniol into one or more low-boiling, medium-boiling, and high-boiling fractions, and removing nerol in liquid or gaseous form as the medium-boiling fraction at a side sampling point of the interlocking distillation column or two thermally coupled distillation columns.

[0127] Therefore, distillation separation is preferably a continuous method for separating nerol in pure or enriched form by distilling it off from a mixture of substances containing nerol and geraniol. The distillation removal is carried out in a partitioned column or an interconnection of two thermally coupled distillation columns with 80 to 200 theoretical plates and one or more side sampling points at an absolute operating pressure of 5 to 200 mbar (i.e., the absolute pressure in the partitioned column or the interconnection of two thermally coupled distillation columns).

[0128] The adjacent tower has 80 to 200, preferably 100 to 180 theoretical plates and one or more, preferably 1 to 3, particularly preferably 1 or 2 side sampling points.

[0129] Preferably, the method for producing pure or enriched neraldehyde, carried out in the context of the method according to the invention, is conducted in a partitioned column or in an interconnection of two thermally coupled distillation columns at an absolute operating pressure of 5 to 200 mbar, preferably 5 to 100 mbar, particularly preferably 5 to 70 mbar, and very particularly preferably 10 to 50 mbar, and especially preferably 10 to 40 mbar. Preferably, the partitioned column or the interconnection of two thermally coupled distillation columns is operated such that the absolute top pressure is 10 to 50 mbar, preferably 10 to 40 mbar. Likewise, preferably, the partitioned column or the interconnection of two thermally coupled distillation columns is operated such that the absolute bottom pressure is 5 to 200 mbar, preferably 10 to 100 mbar, and especially preferably 20 to 50 mbar.

[0130] The reflux ratio can vary over a wide range and is typically from about 5:1 to about 2000:1, preferably from about 20:1 to 1000:1. A fractionating process is also advantageous, where only the reflux is condensed in the top condenser of the column and the feed is returned to the column. In this energy-advantageous partial condensation case, the top product to be discharged is entirely generated in an aftercooler that can operate at a lower temperature.

[0131] The term "neraldehyde in enriched form" should be understood to mean a mixture of neraldehyde-containing substances having a higher content of neraldehyde than the neraldehyde / geranialdehyde mixture used in step 0). For example, such enrichment can increase the neraldehyde content by at least 10%, at least 25%, at least 50%, at least 75%, or at least 85% by weight compared to the neraldehyde / geranialdehyde mixture used in step 0). Preferably, the term "neraldehyde in enriched form" (or equivalent terms such as pure or enriched neraldehyde or similar terms) should be understood to mean neraldehyde having a purity (i.e., neraldehyde content) of 80% to 95% by weight, preferably 85% to 95% by weight, and very particularly preferably 90% to 95% by weight, based on the total amount of the respective mixture. The method according to the invention also allows for the production of neraldehyde in pure form (cis-citral). The term "neraldehyde in pure form" should be understood to mean neraldehyde having a content of 95%, 96%, or 97%, preferably 98%, and particularly preferably 98% to 99.5% by weight, based on the total amount of the corresponding mixture of substances. Particularly preferably, the term "neraldehyde in pure form" should be understood to mean neraldehyde having a geraniol content of up to 1%, preferably from 0.05% to 0.5%, and particularly preferably from 0.1% to 0.3% by weight. Also preferably, the neraldehyde in pure form obtainable according to the invention has an isocitral content of up to 2%, preferably from 0.1% to 1% by weight, such as isocitral of formulas (IV), (V), and (VI), wherein all data within the context of the invention are based on the total amount of the corresponding mixture of substances.

[0132]

[0133] The term "enriched geranialdehyde" (or equivalent terms such as pure or enriched geranialdehyde or similar terms) should be understood to mean a geranialdehyde-containing mixture having a higher content of geranialdehyde than the nerol / geranialdehyde mixture used in step 0). For example, such enrichment can increase the geranialdehyde content by at least 10%, at least 25%, at least 50%, at least 75%, or at least 85% by weight compared to the nerol / geranialdehyde mixture used in step 0). Preferably, the term "enriched geranialdehyde" should be understood to mean geranialdehyde having a purity (i.e., geranialdehyde content) of 80% to 95%, preferably 85% to 95% by weight, and very particularly preferably 90% to 95% by weight based on the total amount of the respective mixture. The method according to the invention also allows for the production of geranialdehyde (trans-citral) in its pure form. The term "geranialdehyde in pure form" should be understood to mean geranialdehyde having a content of 95%, 96%, or 97%, preferably 98%, and particularly preferably 98% to 99.5% by weight, based on the total amount of the corresponding mixture of substances. Particularly preferably, the term "nerol in pure form" should be understood to mean nerol having a geranialdehyde content of up to 1%, preferably 0.05% to 0.5%, and particularly preferably 0.1% to 0.3% by weight. Also preferably, the geranialdehyde in pure form obtainable according to the invention has an isocitral content of up to 2%, preferably 0.1% to 1% by weight, such as isocitral of formulas (IV), (V), and (VI), wherein all data within the context of the invention are based on the total amount of the corresponding mixture of substances.

[0134] The method according to any one of claims 1 to 17, wherein the method is used to produce a desired mixture of isomers, particularly wherein in step a), a mixture of nerol and geraniol comprising a first mass ratio of nerol to geraniol is irradiated with light, and wherein, after irradiation, a mixture of products having a second mass ratio of nerol to geraniol, different from the first mass ratio of nerol to geraniol, is obtained.

[0135] In a preferred embodiment, in step a), a reactant mixture having a first mass ratio of nerol to geranialdehyde (containing nerol and geranialdehyde, for example, the mixture of substances containing nerol / geranialdehyde used in step 0) is irradiated with light, and wherein, after irradiation, a product mixture having a second mass ratio of nerol to geranialdehyde, different from the first mass ratio of nerol to geranialdehyde, is obtained.

[0136] In a preferred embodiment, the first mass ratio of nerol to geraniol and the second first mass ratio of nerol to geraniol differ from each other by at least 5%, at least 10%, at least 20%, at least 30%, at least 50%, or at least 75%.

[0137] The feed (i.e., the mixture of substances to be used) can be fed in liquid or gaseous form into a partition column or an interconnection of two thermally coupled distillation columns, preferably into a partition column, where it is separated into a top fraction and a bottom fraction, as well as one or more, preferably two or more, side-stream extracts as described above. In one side-stream extract, a valuable nerol product of desired purity is produced. In one specific embodiment, a post-condenser is connected downstream of the top condenser of the column and cooled with a coolant (e.g., a sol), and also produces a low-boiling-point fraction of low nerol.

[0138] For continuous distillation fractionation of multi-substance mixtures, various process variations can be used according to existing technologies. In the simplest case, the feed mixture is fractionated into two fractions: a low-boiling top fraction and a high-boiling bottom fraction. When the feed mixture is fractionated into more than two fractions, multiple distillation columns are required depending on the process variation. To limit the complexity of the apparatus, columns with liquid or gas sidestreams are used in the separation of multi-substance mixtures, if possible.

[0139] The adjacent tower is described in, for example, US 2,471,134; US 4,230,533; EP 0 122 367; EP 0 126 288; EP 0 133 510; Chem. Eng. Technol. 10 (1987) 92-98; Chem.-Ing.-Tech. 61 (1989) Vol. 1, 16-25; Gas Separation and Purification 4 (1990) 109-114; Process Engineering 2 (1993) 33-34; Trans IChemE 72 (1994) Part A 639-644 and Chemical Engineering 7 (1997) 72- 76.

[0140] Step a)

[0141] The method of the present invention includes a) isomerizing neraldehyde, especially enriched or pure neraldehyde, into a mixture of neraldehyde and geranialdehyde by light irradiation, or a) isomerizing geranialdehyde, especially enriched or pure geranialdehyde, into a mixture of neraldehyde and geranialdehyde by light irradiation.

[0142] In embodiments of the present invention, a solution of geranialdehyde or neraldehyde in a solvent is irradiated with light. The solvent is preferably selected from water, dichloromethane, trichloromethane, tetrachloromethane, CS2, C1-C4 alcohols, chlorobenzene, fluorobenzene, trifluoromethylbenzene, acetonitrile, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), ethyl acetate, acetone, and mixtures thereof.

[0143] In an alternative preferred embodiment of the invention, no solvent is present in step a), i.e., geranialdehyde and / or neraldehyde are irradiated in their pure form with light, especially monochromatic light.

[0144] In a preferred embodiment, in step a), geranialdehyde in its pure form is irradiated with light, particularly monochromatic light, or the method according to any one of claims 1, 4 and 5, wherein in step a), nerol in its pure form is irradiated with light, particularly monochromatic light, or the method according to any one of claims 1 to 5, wherein in step a), a mixture comprising geranialdehyde and nerol or composed thereof in their pure forms is irradiated with light, particularly monochromatic light.

[0145] Geranialdehyde and / or neraldehyde can be irradiated with light in the presence of sensitizers.

[0146] For the purposes of this invention, the "(photo)sensitizer" is an organic molecule (usually a dye) or a transition metal complex that, when exposed to irradiation (typically electromagnetic radiation in the UV, visible, or near-IR regions), undergoes "Dexter excitation transfer" (electron exchange excitation transfer): excitation transfer occurs due to an electron exchange mechanism. It requires the overlap of the wavefunctions of the energy donor (sensitizer) and the energy acceptor (nerol / geraniol). It is the dominant mechanism in triplet-triplet energy transfer.

[0147] The sensitizer is preferably selected from [Ir(dF(CF3)ppy)2(bpy)]PF6, (Ir[dF(CF3)ppy]2(dtbbpy))PF6, (Ir[dF(CF3)ppy]2(dtbpy ))PF6, (Ir[dF(Me)ppy]2(dtbbpy))PF6, [Ir(dtbbpy)(ppy)2]PF6, Ir(ppy)3, Ru(bpy)3Cl3, [Ru(bpy) 3](PF6)2, Benzophenone, Thioxanthone-9-one, Mischelone, Tetramethoxy-anthraphenthone, Diacetyl-4,5-bis(carbazole-9-yl)-1,2-dicyanophenylene (2CzPN), 3,4,5,6-Tetra(9H-carbazole-9-yl)phthalonitrile (4CzPN), 1,2,3,5-Tetra(carbazole-9-yl)-4,6-dicyanophenylene (4CzIPN), 4-Methoxythoxanone (4-MeOTX), 3-Methoxythoxanone (3-MeOTX), 2-Methoxythoxanone (2-MeOTX), 3-Fluorothoxanone ( 3-FTX), 2-fluorothioxanthione (2-FTX), 3,6-dimethoxythioxanthione (3,3'-MeOTX), 3,6-difluorothioxanthione (3,3'-FTX), 2-methoxy,7-fluorothioxanthione (2-F,2'-MeOTX), 2,7-dimethoxythioxanthione (2,2'-MeOTX), and 9-trimethyl-10-methylacridinium tetrafluoroborate, trimethyl-10-methylacridinium perchlorate, eosin Y, eosin B, 9,10-diphenylanthracene, 9,10-dicyanoanthracene, Rose Bengal, and mixtures thereof.

[0148] In the described embodiment, irradiation is performed using light in the wavelength range of 300 to 800 nm, particularly within the absorption range of the sensitizer, and typically in the wavelength range of 350 to 490 nm. Examples of light sources used for irradiation include, but are not limited to, high-pressure mercury lamps, xenon lamps, fluorescent lamps, incandescent lamps, electroluminescent lighting devices, etc.

[0149] In the proper sense, “light” is electromagnetic radiation having wavelengths (range) within the visible spectrum (380 to 780 nm). However, for the purposes of this invention, unless otherwise stated, the term “light” also covers the directly adjacent wavelength spectrum, namely near IR (> 780 nm to 1 µm) and near UV (300 to < 380 nm).

[0150] In a preferred embodiment, irradiation includes irradiation with light of wavelengths in the ranges between 300 and 1000 nm, 300 and 490 nm, 300 and 420 nm, 350 and 490 nm, 350 and 370 nm, and 400 and 410 nm, or a combination thereof. In a preferred embodiment, irradiation includes irradiation with light of wavelengths of (approximately) 365 nm or (approximately) 405 nm, or a combination thereof.

[0151] In a preferred embodiment, geranialdehyde is irradiated with monochromatic light in step a).

[0152] In a preferred embodiment, neraldehyde is irradiated with monochromatic light in step a).

[0153] It should be understood that this monochromatic light can also be light within the aforementioned preferred wavelength range.

[0154] Monochromatic light consists of a (small) wavelength bandwidth. It should be understood that monochromatic light can be understood in the broadest sense as commonly understood in the art. For example, monochromatic light can exhibit a half-width of 0 to 50 nm, + / - 0.1 to + / - 40 nm, + / - 0.5 to + / - 30 nm, or + / - 10 to + / - 30 nm relative to the wavelength of the emission peak.

[0155] Those skilled in the art will generally understand that monochromatic light preferably exhibits a full width at half maximum (FWHM) of no more than 150 nm, preferably no more than 100 nm, more preferably no more than 75 nm, even more preferably no more than 60 nm, particularly no more than 50 nm, or no more than 30 nm, or no more than 25 nm, or no more than 10 nm (which may optionally be considered as half-width). For example, the FWHM may be between 1 and 100 nm, between 5 and 60 nm, or between 10 and 60 nm, or between 10 and 30 nm, or between 20 and 30 nm, or between 20 and 60 nm, or between 20 and 60 nm, or between 5 and 20 nm, or between 1 and 10 nm, or between 2 and 20 nm.

[0156] In a preferred embodiment, when monochromatic light and / or illumination light consisting of a certain wavelength range is applied, at least 80%, more preferably at least 90%, and particularly at least 99% of the applied light intensity (e.g., given in candela) may be the specified light.

[0157] Filters separate monochromatic light from broadband light sources; lasers or LEDs directly generate monochromatic light.

[0158] In the embodiments described, irradiation is preferably performed using monochromatic light in the wavelength range of 300 to 800 nm, particularly in the absorption range of the sensitizer, typically in the wavelength range of 350 to 490 nm.

[0159] E.1. The method according to any one of the foregoing embodiments, wherein in step (a), the reaction mixture consisting of nerol or geraniol and a sensitizer and optionally a solvent is irradiated with light in the wavelength range of 300 to 800 nm.

[0160] E.2. The method according to Example E.1, wherein in step (a), the reaction mixture consists of nerol or geranialdehyde and a sensitizer and a solvent.

[0161] E.3. The method according to Example E.1 or E2, wherein in step (a), the reaction mixture consists of nerol or geranialdehyde and a sensitizer.

[0162] E.4. The method according to any one of Examples E.1 to E.3, wherein in step (a), the reaction mixture is irradiated with light in the wavelength range of 350 to 490 nm.

[0163] E.5. The method according to any one of the foregoing embodiments, wherein the reaction mixture is irradiated with monochromatic light in step (a).

[0164] E.6. The method according to embodiment E.13, wherein the irradiation in step (a) is performed using a filter that provides monochromatic light from a broadband light source, wherein at least 90% of the monochromatic light is in the wavelength range of 300 to 800 nm, preferably using a monochromatic light source, more preferably using an electroluminescent lighting device that emits monochromatic light, wherein at least 90% of the light emitted by the monochromatic light source is in the wavelength range of 300 to 800 nm.

[0165] E.7. The method according to embodiment E.6, wherein the irradiation in step (a) is performed using a monochromatic light source, preferably an electroluminescent lighting device that emits monochromatic light, wherein at least 90% of the light emitted by the monochromatic light source is in the wavelength range of 350 to 490 nm.

[0166] E.8. The method according to any one of embodiments E.6 or E.7, wherein the irradiation in step (a) is performed using an electroluminescent lighting device that emits monochromatic light, wherein the electroluminescent lighting device comprises at least one LED.

[0167] In order to carry out isomerization efficiently, the amount of photosensitizer used in the reaction is at a concentration that ensures the absorbance of light in the photoreactor is in the range of 0.1 to 3.0, preferably in the range of 0.5 to 2.5, and most preferably in the range of 1.0 to 2.0.

[0168] Absorbance is defined as the logarithm of the ratio of incident radiation power to transmitted radiation power through the sample (minus the effect of the absorption cell wall).

[0169] In the embodiments described herein, “monochromatic light” as understood herein preferably refers to all radiation emitted in the range of 350 nm to 490 nm, comprising at least 90% of its power and at most 100% of its power. Depending on the nature and amount of the filterless electroluminescent lighting device, photosensitizer, and organic solvent employed, the power percentage of the minor component of monochromatic light outside a given wavelength can be as high as 10%. However, the vast majority of embodiments of monochromatic light contain only a small portion of light outside the range of 350 nm to 490 nm. In one embodiment, monochromatic light should be understood as a physical entity in which at least 95% of its power and at most 100% of its power are emitted in the range of 350 nm to 490 nm. In yet another embodiment, monochromatic light means that at least 98% of its power, and more preferably at least 99%, and at most 100% of its power are emitted in the range of 350 nm to 490 nm. The amount of monochromatic light is expressed in terms of power because doing so eliminates the need to define permissible amounts of light above and below the claimed wavelength range in other ways, in lumens (lm), watts (Wh), or candela (cd). When not expressed in terms of power, the amount will vary as a function of the wavelength under consideration. In yet another specific embodiment, as understood within this disclosure, monochromatic light is all radiation emitted in the range of 350 nm to 490 nm, comprising at least 90% of its power and at most 100% of its emission, and preferably exhibiting a half-width of no more than + / - 100 nm, preferably no more than + / - 60 nm, such as + / - 10 to + / - 30 nm, relative to the wavelength of the emission peak. This defined half-width provides a highly structured illumination signal, which results in increased nerol / geraniol yields.

[0170] In a more preferred alternative embodiment of the invention, no sensitizer is present in step a).

[0171] In the embodiment described, the irradiation is preferably performed using monochromatic light in the wavelength range of 300 to 800 nm, particularly in the wavelength range of 300 to 420 nm.

[0172] F.1 The method according to any one of the foregoing embodiments, wherein in step (a), the reaction mixture consisting of nerol or geranialdehyde and optionally a solvent is irradiated with light in the wavelength range of 300 to 800 nm.

[0173] F.2 The method according to Example F.1, wherein in step (a), the reaction mixture consists of nerol or geranialdehyde and a solvent.

[0174] F.3 The method according to Example F.1 or F.2, wherein in step (a), the reaction mixture consists of nerol or geranialdehyde.

[0175] F.4 The method according to any one of Examples F.1 to F.3, wherein in step (a), the reaction mixture is irradiated with light in the wavelength range of 300 to 420 nm.

[0176] F.5 The method according to any one of the foregoing embodiments, wherein the reaction mixture is irradiated with monochromatic light in step (a).

[0177] F.6 The method according to embodiment F.5, wherein the irradiation in step (a) is performed using a filter that provides monochromatic light from a broadband light source, wherein at least 90% of the monochromatic light is in the wavelength range of 300 to 800 nm, preferably using a monochromatic light source, more preferably using an electroluminescent lighting device that emits monochromatic light, wherein at least 90% of the light emitted by the monochromatic light source is in the wavelength range of 300 to 800 nm.

[0178] F.7 The method according to embodiment F.6, wherein the irradiation in step (a) is performed using a monochromatic light source, preferably an electroluminescent lighting device that emits monochromatic light, wherein at least 90% of the light emitted by the monochromatic light source is in the wavelength range of 300 to 420 nm.

[0179] F.8 The method according to embodiment F.6 or F.7, wherein the irradiation in step (a) is performed using an electroluminescent lighting device that emits monochromatic light, wherein the electroluminescent lighting device consists of at least one LED.

[0180] In a preferred embodiment, in step a), geranialdehyde is irradiated with light in the wavelength range of 300 to 420 nm, particularly monochromatic light; or in step a), neraldehyde is irradiated with light in the wavelength range of 300 to 420 nm, particularly monochromatic light; or in step a), a mixture comprising geranialdehyde and neraldehyde, or composed thereof, in pure form is irradiated with light, particularly monochromatic light.

[0181] Preferably, at least 90% and at most 100% of the radiant flux of the light, particularly monochromatic light, is emitted in the range of 300 nm to 420 nm, and its single-peak emission spectrum preferably exhibits a half-width of no more than + / - 100 nm, preferably no more than + / - 60 nm, such as + / - 10 to + / - 30 nm, relative to the wavelength of the emission peak, and / or

[0182] Preferably, geranialdehyde, neraldehyde, or a mixture thereof containing neraldehyde and geranialdehyde in their pure form, or composed thereof, is irradiated with light, particularly monochromatic light, as indicated above.

[0183] In the embodiments described herein, “monochromatic light” as understood herein preferably refers to all radiation emitted with at least 90% of its power and at most 100% of its power in the range of 300 nm to 420 nm. Depending on the filterless electroluminescent lighting device employed, the nature and amount of the organic solvent, the power percentage of the minor component of monochromatic light outside a given wavelength can be as high as 10%. However, the vast majority of embodiments of monochromatic light contain only a small portion of light outside the range of 300 nm to 420 nm. In one embodiment, monochromatic light should be understood as a substance emitted with at least 95% of its power and at most 100% of its power in the range of 300 nm to 420 nm. In yet another embodiment, monochromatic light means that at least 98% and more preferably at least 99% of the power of the monochromatic light emitted with at most 100% of its power in the range of 300 nm to 420 nm. The amount of monochromatic light is expressed in terms of power because doing so eliminates the need to define permissible amounts of light above and below the claimed wavelength range in other ways, in lumens (lm), watts (Wh), or candela (cd). When not expressed in terms of power, the amount will vary as a function of the wavelength under consideration. In yet another specific embodiment, as understood within this disclosure, monochromatic light is all radiation emitted in the range of 300 nm to 420 nm, comprising at least 90% of its power and at most 100% of its emission, and its single-peak emission spectrum preferably exhibits a half-width of no more than + / - 100 nm, preferably no more than + / - 60 nm, such as + / - 10 to + / - 30 nm, relative to the wavelength of the emission peak. This defined half-width provides a highly structured illumination signal, which results in increased nerol / geraniol yields.

[0184] Irradiation with light is preferably accomplished by using LEDs (light-emitting diodes) or lasers.

[0185] As used in this context, the term "LED" can also refer to an organic light-emitting diode (OLED), an active-matrix organic light-emitting diode (AMOLED), or any other diode-based lighting source. Preferably, LED refers to a high-power LED that can be used with an electrical power of 350 mW or higher. Preferably, the LED is configured to apply an electrical power of more than 1 W.

[0186] The light emitted by the LED unit is selected such that at least a portion of the light can be used in the isomerization. Preferably, the LED unit is adapted to emit light in the ultraviolet and (optionally) visible portions of the electromagnetic spectrum, preferably having a wavelength between 300 and 800 nm, more preferably between 300 and 420 nm or 350 and 490 nm.

[0187] The filterless electroluminescent lighting device disclosed herein is any light-emitting electroluminescent device that does not contain a filter. A filter can be a layer, compound, or chemical product applied to the lighting device. A filter can also be a compound immersed or dissolved in a solvent circulated, pumped, or floated around the lighting device and adapted to absorb light within a specific range without transferring energy emitted from the absorbed light to nerol / geranialdehyde. The electroluminescent lighting device is required to operate without relying on any kind of chemically induced lighting (such as gas ionization) or heating. A filterless electroluminescent lighting device is understood to provide light (photons) generated from electron-deficient holes or gaps in electron-poor materials and to emit electromagnetic radiation (preferably in the form of visible light). The filterless electroluminescent lighting device is selected from the group consisting of: luminescent electrochemical cell units, electroluminescent lines, field-electroluminescent polymers, light-emitting diodes, organic light-emitting diodes, polymer light-emitting diodes, active-matrix organic light-emitting diodes (AMOLEDs), electroluminescent films (especially those based on inorganic light-emitting materials), semiconductor lasers, and diode lasers. Electroluminescent lighting devices include chemical lasers, dye lasers, free-electron lasers, gas-powered lasers, gas lasers, ion lasers, laser flashlights, metal vapor lasers, nonlinear optical quantum well lasers, ruby ​​lasers, solid-state lasers, etc.

[0188] In a preferred embodiment, geranialdehyde is irradiated with light in the wavelength range of 350 to 490 nm, particularly monochromatic light, in step a); or neraldehyde is irradiated with light in the wavelength range of 350 to 490 nm, particularly monochromatic light, in step a).

[0189] Preferably, at least 90% and at most 100% of the radiant flux of the light, particularly monochromatic light, is emitted in the range of 350 nm to 490 nm, and its single-peak emission spectrum preferably exhibits a half-width of no more than + / - 100 nm, preferably no more than + / - 60 nm, such as + / - 10 to + / - 30 nm, relative to the wavelength of the emission peak, and / or

[0190] Preferably, geranialdehyde and / or nerol are irradiated in the presence of a sensitizer.

[0191] In another detailed embodiment of the method of the invention, at least 90% and at most 100% of the power of the monochromatic light is emitted in the range of 300 nm to 420 nm, or 350 nm to 490 nm. However, by means of a narrower wavelength spectrum (and thus less power and energy consumption), operation in this slightly smaller wavelength range still provides good conversion rates to nerol / geraniol and high yields of nerol / geraniol. Side reactions, such as isomerization into undesirable compounds, are further suppressed or preferably completely avoided in this wavelength range. The narrowing of the wavelength range in a filterless electroluminescent illumination device is achieved by selectively controlling discrete electronic components within the device.

[0192] Irradiation can be carried out in a continuously stirred reactor, in a pumping loop, or in a continuous flow reactor.

[0193] The lighting apparatus and photochemical reactor described in WO 2021 / 233951 and / or WO 2023 / 011951A1 can be used to perform step a) of the method of the present invention.

[0194] Step a) is preferably performed in a temperature range of -20°C to 100°C.

[0195] Step a) is preferably performed within a pressure range of 1 to 20 bar.

[0196] Step b)

[0197] In a preferred embodiment, the method according to the invention includes separating the mixture containing geranialdehyde and nerol obtained in step a) as step b) to obtain enriched or pure geranialdehyde and enriched or pure nerol, especially by distillation or chromatographic separation methods.

[0198] In a more preferred embodiment, the method according to the invention comprises (continuous) distillation separation of the mixture containing geranialdehyde and neraldehyde obtained in step a) as step b) to obtain enriched or pure geranialdehyde and enriched or pure neraldehyde. Refer to WO 2009 / 068444 and the detailed description of step a) above. With respect to step b), the same preferences apply as for step a). If the process in step a) is carried out by light irradiation in the presence of a solvent and / or sensitizer, step b) also involves distillation to remove the solvent and separate the sensitizer, which is retained as a residue in the distillation and optionally reused in step a).

[0199] Distillation separation is a continuous method for separating geranialdehyde in pure or enriched form by distilling it off from a mixture of substances containing neraldehyde and geranialdehyde. The distillation removal is carried out in a partitioned column or an interconnection of two thermally coupled distillation columns with 80 to 200 theoretical plates and one or more side sampling points at an absolute operating pressure of 5 to 200 mbar (i.e., the absolute pressure in the partitioned column or the interconnection of two thermally coupled distillation columns).

[0200] Distillation separation is preferably a continuous method for separating nerol in pure or enriched form by distilling it off from a mixture of substances containing nerol and geraniol. The distillation removal is carried out in a partitioned column or an interconnection of two thermally coupled distillation columns with 80 to 200 theoretical plates and one or more side sampling points at an absolute operating pressure of 5 to 200 mbar (i.e., the absolute pressure in the partitioned column or the interconnection of two thermally coupled distillation columns).

[0201] The adjacent tower has 80 to 200, preferably 100 to 180 theoretical plates and one or more, preferably 1 to 3, particularly preferably 1 or 2 side sampling points.

[0202] Step b) is carried out in a partitioned column or in the interconnection of two thermally coupled distillation columns at an absolute operating pressure of 5 to 200 mbar, preferably 5 to 100 mbar, particularly preferably 5 to 70 mbar, and very particularly preferably 10 to 50 mbar, and especially preferably 10 to 40 mbar. Preferably, the partitioned column or the interconnection of two thermally coupled distillation columns is operated such that the absolute top pressure is 10 to 50 mbar, preferably 10 to 40 mbar. Also preferably, the partitioned column or the interconnection of two thermally coupled distillation columns is operated such that the absolute bottom pressure is 5 to 200 mbar, preferably 10 to 100 mbar, and especially preferably 20 to 50 mbar.

[0203] The reflux ratio can vary over a wide range and is typically from about 5:1 to about 2000:1, preferably from about 20:1 to 1000:1. A fractionating process is also advantageous, where only the reflux is condensed in the top condenser of the column and the feed is returned to the column. In this energy-advantageous partial condensation case, the top product to be discharged is entirely generated in an aftercooler that can operate at a lower temperature.

[0204] The feed (i.e., the mixture of substances to be used) can be fed in liquid or gaseous form into a partition column or an interconnection of two thermally coupled distillation columns, preferably into a partition column, where it is separated into a top fraction and a bottom fraction, as well as one or more, preferably two or more, side-stream extracts as described above. In one side-stream extract, a valuable neraldehyde product (or a valuable geranialdehyde product) is produced with desired purity.

[0205] In a particularly preferred embodiment, the present invention relates to a method for preparing enriched or pure neraldehyde.

[0206] In another preferred embodiment, the present invention relates to a method for preparing enriched or pure geranialdehyde.

[0207] Step 0) includes distillation to separate the mixture containing geranialdehyde and nerol to obtain enriched or pure geranialdehyde and nerol.

[0208] The mixture of substances used in step 0) preferably consists of 30% to 70%, preferably 40% to 60% by weight of nerol, 70% to 30%, preferably 60% to 40% by weight of geraniol, and 0% to 5% by weight of other components, wherein the total percentages reach 100% by weight.

[0209] In step a), the enriched or pure geranialdehyde obtained in step 0) is isomerized into a mixture of nerol and geranialdehyde by light irradiation. Preferably, the enriched or pure geranialdehyde is irradiated in a pure form, i.e., without solvents and photosensitizers. The isomerization of the enriched or pure geranialdehyde into nerol and geranialdehyde is balanced by light irradiation.

[0210] Surprisingly, isomerization of neraldehyde or geranialdehyde by light irradiation does not lead to a thermodynamic equilibrium between neraldehyde and geranialdehyde (approximately 40% neraldehyde / approximately 60% geranialdehyde, according to Figure 1 of Wolken et al., J. Agric. Food Chem. 2000, 48, 5401-5405). That is, in mixtures of neraldehyde and geranialdehyde obtained by light irradiation, the amount of neraldehyde is generally higher than that of geranialdehyde. This fact is advantageous for the production of neraldehyde.

[0211] Step a) is preferably performed in a temperature range of -20°C to 100°C.

[0212] Step a) is preferably performed within a pressure range of 1 to 20 bar.

[0213] Step b) involves distilling the mixture containing geranialdehyde and neraldehyde obtained in step a) to obtain enriched or pure geranialdehyde and neraldehyde. The neraldehyde product is collected.

[0214] The (undesired) enriched or purified geranialdehyde obtained in step b) is recycled in step a) according to step c), i.e., by isomerization with light irradiation to a (photo) equilibrium between nerol and geranialdehyde. Recycling the (undesired) enriched or purified geranialdehyde obtained in step b) to step a) allows for an increased yield of enriched or purified nerol in the method of the present invention.

[0215] From an equipment perspective, it is economical to use a continuous reaction unit to efficiently and continuously obtain neraldehyde through distillation, while simultaneously performing photoisomerization of geranialdehyde in the collection section of the distillation column.

[0216] As indicated above, the nerol:geranium mass ratio of the reactants (e.g., a mixture containing nerol and geraniol) can be altered by means of the method of the present invention. Therefore, the obtainable (or acquired) product can have distinctive characteristics.

[0217] Therefore, another aspect of the invention relates to a mixture comprising nerol and geraniol, which can be obtained (or acquired) by the method of the invention.

[0218] It should be understood that the definitions and preferred embodiments set forth in the context of the methods of isomerizing nerol to geranialdehyde and / or isomerizing geranialdehyde to nerol of the present invention are adapted, with necessary modifications, to mixtures (or mixtures) obtainable by such methods.

[0219] In a preferred embodiment, the mixture has a nerol:geraniol mass ratio of >1.25 or <0.75, particularly >1.5. In a preferred embodiment, the mixture has a nerol:geraniol mass ratio of >1.75 or >2.0 or >3.0. This can be achieved by isomerization in step a), optionally in combination with enrichment of nerol.

[0220] In an alternative preferred embodiment, the mixture has a nerol:geraniol mass ratio of <0.7 or >0.6 or >0.5. This can be achieved by isomerization in step a), optionally in conjunction with enriching geraniol.

[0221] In another alternative preferred embodiment, the mixture has a nerol:geraniol mass ratio between 1:1.25 and 1.25:1.

[0222] Further conversion to menthol or linalool

[0223] The nerol or geraniol obtained by the method according to the invention is a usable intermediate in the production of, for example, menthol or linalool.

[0224] The neraldehyde or geranialdehyde obtained by the method according to the present invention, especially neraldehyde, can be used to produce menthol, especially optically active menthol.

[0225] Therefore, the method according to the present invention may include

[0226] - Additional steps d.1) to g.1):

[0227] d.1) Catalytically hydrogenating nerol obtained by the method of the present invention (e.g., according to any one of claims 1-3, 6-16, 18-23), preferably nerol obtained in any one of steps 0), a), and / or b) (e.g., 0) and / or b), or a) and / or b)) to obtain citronellol.

[0228] e.1) Cyclization of citronellol in the presence of an acidic catalyst to obtain isopreneol.

[0229] f.1) Optionally purify isomenthol, preferably by crystallization, and

[0230] g.1) Catalytically hydrogenate isoprene to obtain menthol. See WO 2009068444 and D. Dylong et al., Flavour Fragr. J., 37 (2022) 195-209.

[0231] The overall reaction sequence is illustrated by the following reaction scheme.

[0232]

[0233] Step d.1): Catalytically hydrogenate nerol and / or geraniol to obtain citronellol.

[0234] According to stage d.1) of the method for producing menthol, catalytic hydrogenation of nerol is carried out to obtain citronellol, preferably catalytic hydrogenation of nerol produced as described above. See WO 2009768444, Jäkel C, Paciello R. The asymmetric hydrogenation of enones - access to a new L-menthol synthesis, in: Blaser HU, Federsel HJ, ed. Asymmetric Catalysis on Industrial Scale: Challenges, Approaches, and Solutions. 2nd ed. Wiley-VCH; 2010:187-205; and Stolle A, Gallert T, Schmöger C, Ondruschka B. Hydrogenation of citral: a wide-spread model reaction for selective reduction of , -unsaturated aldehydes [hydrogenation of citral: used for selective reduction] , "Universal model reactions of unsaturated aldehydes." RSC Adv [Progress of the Royal Society of Chemistry]. 2013;3(7):2112-2153.

[0235] The method of using WO 2006 / 040096 (which is hereby incorporated herein in its entirety, and which (including all preferred embodiments) should be considered part of this disclosure) for making , An improved method for producing optically active carbonyl compounds by asymmetric hydrogenation of unsaturated carbonyl compounds in the presence of an optically active transition metal catalyst that is soluble in the reaction mixture and has at least one carbon monoxide ligand, and a method that may preferably be used in the context of this invention.

[0236] According to WO 2016 / 097242A1, the catalytic activity of optically active transition metal catalysts (containing rhodium as the catalytically active transition metal) for the homogeneous catalytic asymmetric hydrogenation of geranialdehyde / nervone can be significantly increased by adding phosphine compounds, such as...

[0237] - (2-(diphenylphospho)-1-methylpropyl))diphenylphosphine, including its (R,R)-enantiomer (=(R,R)-chiraphos-oxide) and its (S,S)-enantiomer (=(S,S)-chiraphos-oxide) and its racemic mixture (compound (I-1)).

[0238] - Cyclopentyldiphenylphosphine (compound (I-2),

[0239] - 2-Butyldiphenylphosphine (compound (I-3),

[0240] - Cyclohexyldiphenylphosphine (compound (I-4),

[0241] - Isopropyl diphenylphosphine (compound (I-5),

[0242] - [5-(diphenylphosphinemethyl)-2,2-dimethyl-1,3-dioxolane-4-yl]methyldiphenylphosphine monooxide, including its (4S,5S) and (4R,5R) enantiomers and their racemic mixtures (compound (I-6),

[0243] - [5-(1-diphenylphosphine ethyl)-2,2-dimethyl-1,3-dioxolane-4-yl]ethyldiphenylphosphine monooxide, including its (4S,5S) and (4R,5R) enantiomers and their racemic mixtures (compound (I-7),

[0244] -[2-Diphenylphosphine cyclohexyl]diphenylphosphine monooxide, including its (1S,2S) and (1R,2R) enantiomers and their racemic mixtures (compound (I-8),

[0245] - [4-Diphenylphosphine tetrahydrofuran-3-yl]diphenylphosphine monooxide, including its (3S,4S) and (3R,4R) enantiomers and their racemic mixtures (compound (I-9),

[0246] - [2-Diphenylphosphonyl-3-bicyclo[2.2.1]hept-5-enyl]diphenylphosphonate monooxide, including its (1S,2R,3R,4R), (1R,2S,3R,4R), (1S,2R,3S,4S), (1R,2S,3S,4S) isomers, and mixtures of its enantiomers and diastereomers (compound (I-10)).

[0247] - [1-benzyl-4-diphenylphosphylpyrrolidine-3-yl]diphenylphosphine monooxide, including its (3S,4S) and (3R,4R) enantiomers and their racemic mixtures (compound (I-11),

[0248] - [3-Diphenylphosphonyl-1-methylbutyl]diphenylphosphine monooxide, including its (1S,3S) and (1R,3R) enantiomers and their racemates (compound (I-12), and mixtures thereof), without significantly or adversely affecting their stability and selectivity.

[0249] Racemic or optically active citronellol obtained in this manner is typically produced in high yields and, in particular, with high chemical and optical purity. Depending on the required chemical purity of the resulting citronellol, preferably D-citronellol, which is to be further reacted in a further step d.1), it can be further purified by separation and / or purification methods known to those skilled in the art. Pre-purification of the citronellol-containing product mixture obtained by hydrogenation of the present invention using a falling film evaporator, followed by distillation of the citronellol, has proven advantageous.

[0250] Another aspect of the present invention relates to a method for preparing citronellal, preferably optically active citronellal, comprising the following steps:

[0251] d.0) Optionally, citral having a neraldehyde:geranium mass ratio as available (or obtainable) according to the invention, preferably having a neraldehyde:geranium mass ratio > 1, preferably > 1.5, is separated into geranium and neraldehyde; and

[0252] d.1) Prepare optically active citronellol by asymmetric hydrogenation of citral or citral having a nerol:geranium mass ratio as obtained (or obtained) according to the present invention, preferably having a nerol:geranium mass ratio of >1, preferably >1.5.

[0253] Another aspect of the invention relates to citronellol, which may optionally be optically active citronellol, which can be obtained (or acquired) by the method of the invention.

[0254] It should be understood that the definitions and preferred embodiments set forth in the context of the methods of the present invention and the obtainable (or obtained) products described above, with necessary modifications, are applicable to the preparation and product characteristics of isoprementol. It should be understood that the obtainable (or obtained) isoprementol has certain characteristics.

[0255] Isoprene (5-methyl-2-(1-methylvinyl)-cyclohexanol) can have three asymmetric carbon atoms and therefore has four stereoisomers, each existing as a pair of enantiomers. (1R,3R,4S)-(-)isoprene is also known as L-isoprene.

[0256] Another aspect of the present invention relates to a method for preparing isomenthol, preferably optically active isomenthol, preferably L-isomenthol, comprising the following steps:

[0257] (d.0) Optionally, citral having a neraldehyde:geranium mass ratio as available (or obtainable) according to the invention, preferably having a neraldehyde:geranium mass ratio of >1, preferably >1.5, is separated into geranium and neraldehyde;

[0258] d.1) Prepare optically active citronellol by asymmetric hydrogenation of citral or citral having a nerol:geranium mass ratio as obtained (or acquired) according to the present invention, preferably having a nerol:geranium mass ratio > 1, preferably > 1.5; and

[0259] e.1) Cyclize the citronellal from step d.1) in the presence of a suitable acid, preferably a Lewis acid, to obtain isoprene.

[0260] Another aspect of the invention relates to isomenthol, which may optionally be optically active isomenthol, preferably L-isomenthol, which can be obtained (or acquired) by the method of the invention.

[0261] It should be understood that the definitions and preferred embodiments set forth in the context of the methods of the present invention and the obtainable (or obtained) products described above, with necessary modifications, are applicable to the preparation and product characteristics of isoprementol. It should be understood that the obtainable (or obtained) isoprementol has certain characteristics.

[0262] Another aspect of the present invention relates to a method for preparing menthol, preferably L-menthol, comprising the following steps:

[0263] d.0) Optionally, citral having a neraldehyde:geranium mass ratio as available (or obtained) according to the invention, preferably having a neraldehyde:geranium mass ratio of >1, preferably >1.5, is separated into geranium and neraldehyde;

[0264] d.1) Prepare optically active citronellol by asymmetric hydrogenation of citral or citral having a nerol:geranium mass ratio as obtained (or obtained) according to the present invention, preferably having a nerol:geranium mass ratio of >1, preferably >1.5.

[0265] e.1) Cyclize the citronellol from step d.1) in the presence of a suitable catalyst to obtain isopreneol;

[0266] f.1.) Optionally purify isomenthol, for example, by crystallization; and

[0267] g.1) Catalytically hydrogenate the isomenthol prepared in either step e.1) or f.1) to obtain menthol.

[0268] Another aspect of the invention relates to a method for preparing optically active menthol, the method using neraldehyde and / or geranialdehyde obtained by the method according to the invention, particularly pure neraldehyde or a mixture of neraldehyde and geranialdehyde containing a neraldehyde:geranialdehyde mass ratio of >1, preferably >1.5.

[0269] Another aspect of the present invention relates to a method for preparing optically active menthol, preferably L-menthol, comprising the following steps:

[0270] Optionally, citral having a neraldehyde:geranaldehyde mass ratio as available (or obtainable) according to the invention can be separated into geranaldehyde and neraldehyde;

[0271] Optically active citronellol was prepared by asymmetric hydrogenation of citral.

[0272] The optically active citronellol prepared in this manner is cyclized in the presence of a suitable acid, preferably a Lewis acid, to obtain optically active isopreneol, and

[0273] The optically active isomenthol prepared in this manner is hydrogenated to obtain optically active menthol.

[0274] Another aspect of the invention relates to menthol, which may optionally be optically active menthol, particularly L-menthol, which can be obtained (or acquired) by the method of the invention.

[0275] It should be understood that the definitions and preferred embodiments set forth in the context of the methods of the present invention and the obtainable (or obtained) products described above, with necessary modifications, are applicable to the preparation and product characteristics of menthol. It should be understood that the obtainable (or obtained) menthol has certain characteristics.

[0276] This article provides preferred embodiments for the preparation of menthol.

[0277] Step e.1): Cyclic acid citronellol to obtain isoprene.

[0278] According to step e.1) of the method of the present invention, cyclization of citronellol, which has been obtained by catalytic hydrogenation of nerol in step d.1) above, is carried out in the presence of an acidic catalyst to yield isoprene. See WO2006092433A1 and US 7550633.

[0279] It has long been known that citronellol cyclizes to isoprene under acidic conditions. An overview of available acidic or Lewis acidic reagents or catalysts can be found, for example, EJ Lenardao, GV Botteselle, F. de Azambuja, G. Perin, RG Jacob Tetrahedron [Tetrahedron] 2007, 63, 6671-6712.

[0280] A wide variety of systems are referred to as conventional catalysts and reagents, such as silica gel or alumina or mixtures thereof, as disclosed, for example, in WO 2004 / 089299, zeolites, as described, for example, in the case of boron-containing zeolites in WO 2004 / 101480. Other conventional acidic or Lewis acidic catalysts are, for example, zinc bromide, as described, for example, in Synthesis [Synthesis] 1978, 147-148 and EP 1053974A1, or additionally, tungstic acids as described in BR 2005002489A.

[0281] Furthermore, EP 1225163A describes the cyclization of citronellol to isoprene in the presence of a tris(2,6-diphenylphenol)aluminum catalyst. Tris(2,6-diphenylphenol)aluminum is known in the literature and has been used as a catalyst for… , Selective 1,4-functionalization of unsaturated carbonyl compounds and for specific Claisen rearrangements, as described, for example, in Angew. Chem. Int. Ed. [Applied Chemistry International Edition] 2004, 43, 994. The specified catalyst system is also suitable for use in step e.1) of the method according to the invention.

[0282] WO 2007 / 039342 and WO 2007 / 039366 also disclose aluminum-containing homogeneous catalysts, specifically those having one or more siloxide ligands on aluminum. The disclosed aluminum-siloxide compounds are suitable as catalysts for intramolecular Prins reactions, including the cyclization of citronellol to isoprene.

[0283] The cyclization of citronellol to isoprene is preferably carried out in the presence of an aluminum-containing catalyst, specifically in the presence of a Lewis acidic aluminum-containing catalyst, according to step e.1).

[0284] WO 2006 / 092433 (which is hereby incorporated in its entirety and whose disclosures, including all preferred and exemplary embodiments, should be considered part of this disclosure) describes a particularly preferred method for cyclizing citronellol to isoprene in the context of step e.1) of the method according to the invention.

[0285] Cycling citronellal to isoprene can be achieved by cyclization in the presence of at least one Lewis acidic aluminum-containing catalyst, such as a bis(diarylphenoxy)aluminum compound, which may be used in the presence of an auxiliary agent such as a carboxylic anhydride. Isoprene can be recovered from the reaction product containing the catalyst by distillation, yielding an isoprene-rich top product and an isoprene-poor bottom product. At least one catalyst can be regenerated from the bottom product. The isoprene obtained by cyclization of citronellal in this manner can be further purified by suitable separation and / or purification methods (particularly by crystallization) and is at least largely free of undesirable impurities or byproducts.

[0286] Step f.1): Purification of isoprene by crystallization

[0287] In step f.1) of the method according to the invention, isoprene, which is available as described in step e.1) of the method according to the invention above, is purified by crystallization.

[0288] Crystallization of isoprene is known to those skilled in the art and is disclosed, for example, in US 5,663,460. This patent describes the purification of (-)-n-isomenthone by crystallization from petroleum ether or advantageously from acetone at temperatures ranging from -20°C to -60°C. An increase in optical purity can also be achieved here.

[0289] Furthermore, US 3,218,361 discloses a method for crystallizing isoprene from a mixture of substances comprising isoprene and its diastereomers. Crystallization is carried out here at a temperature below 0°C, preferably below -30°C and, for example, at -65°C, and can be carried out from a solution or from a melt.

[0290] WO 2007 / 023109 (which is hereby incorporated in its entirety and whose disclosures, including all preferred and exemplary embodiments, should be considered part of this disclosure) discloses a method for producing enriched isomenthol, specifically enriched L-isomenthol, by crystallization from a melt containing L-isomenthol.

[0291] This method for purifying isomenthol, specifically optically active L-isomenthol, by melt crystallization constitutes a preferred method for purifying isomenthol by crystallization according to step f.1).

[0292] Isopyrrolidone obtained by crystallization as described in step e.1) of the method according to the invention above can also be further purified by other separation methods, preferably by distillation. In this regard, the use of interconnected, thermally coupled columns has proven advantageous from a processing and cost perspective.

[0293] Step g.1): Catalytic hydrogenation of isomenthol to obtain menthol.

[0294] According to step g.1) of the method of the present invention, the catalytic hydrogenation of isoprene obtained according to step f.1) to menthol is carried out. See WO 2009068444A2 and WO 2009013192A2.

[0295] In the context of a preferred embodiment, the catalytic hydrogenation of racemic or optically active isoprene in step g.1) of the method according to the invention is carried out in the presence of a heterogeneous nickel-containing catalyst. When using isoprene rich in enantiomers or enantiomerically pure isoprene, preferably L-isoprene, the catalytic hydrogenation according to step g.1) is preferably carried out in the presence of a heterogeneous nickel- and copper-containing catalyst.

[0296] DE 577036 discloses a method for the synthesis of menthol via the hydrogenation of thymol. Nickel, nickel / copper, and cobalt catalysts are described as suitable catalysts.

[0297] As described in GB 1,503,723, specific nickel catalysts have also been used for the catalytic hydrogenation of piperine to obtain menthol.

[0298] EP 1532091 discloses a method for producing racemic menthol by catalytic hydrogenation of isoprene, wherein the isoprene is used in the form of a mixture of diastereomers of 70.1% isoprene, 18.1% neo-isoprene, 6.8% iso-isoprene, and 2.6% neo-isoprene. The catalyst used is Raney nickel doped with iron and chromium. This yields menthol in the form of a mixture of possible diastereomers, consisting of 61.4% menthol and 35.6% of another diastereomer of menthol.

[0299] Another route for obtaining menthol is the method for diastereoselectively cyclizing citronellol to isomenthol, as described, for example, in EP 1225163 or WO 2006 / 092433. The isomenthol obtained in this manner can then be hydrogenated to menthol in a further step.

[0300] RH Pickard et al. described the production of L-menthol by catalytic hydrogenation of L-isomenthol in the presence of colloidal palladium in J. Chem. Soc. 1920, 1248-1263.

[0301] B. Dudley Sully et al. described the production of L-menthol by hydrogenation of L-isomenthol at 120°C in the presence of Raney nickel in P.&EOR 1068, 235-366.

[0302] EP 1053974 discloses a method for catalytically hydrogenating isoprene to menthol in the presence of a 5% palladium / carbon catalyst at a hydrogen pressure of 5 bar.

[0303] EP 0394842 relates to catalysts for hydrogenating aliphatic unsaturated compounds, comprising nickel and copper and characterized by contents of 20% to 75% nickel oxide, 10% to 75% zirconium dioxide, and 5% to 50% copper oxide by weight, in each case based on an oxidized, unreduced catalyst. Examples of specified substrates are: butyn-2-diol-1,4, buten-2-diol-1,4, and 2-ethylhexen-2-aldehyde.

[0304] According to a particularly preferred embodiment within the context of step g.1) of the method according to the invention, for the production of racemic or optically active menthol ( The method involves making racemic or optically active isoprene () Catalytic hydrogenation is carried out in the presence of hydrogen and a catalyst containing...

[0305] - 30% to 70% by weight of nickel oxides, calculated as NiO,

[0306] - 15% to 45% by weight of zirconium oxides, calculated as ZrO2.

[0307] - 5% to 30% by weight of copper oxides, calculated as CuO, and

[0308] - 0.1% to 10% by weight of molybdenum oxides, calculated as MoO3,

[0309] The data, expressed as a percentage by weight, are based on dry, unreduced catalyst.

[0310] The catalyst used, particularly preferably, in step g.1) of the method according to the invention comprises, by weight, 49% to 53% NiO, 15% to 19% CuO, 28% to 32% ZrO2, and 1% to 2% MoO3, and optionally 0% to 3% of other components (e.g., graphite), wherein the total weight fraction of the selected individual components in each case reaches 100% by weight. Catalysts of this type are known and can be produced, for example, as described in EP 0696572 (which is referred to in its entirety in this document). The catalyst in step g.1) can be produced, for example, as described on pages 65 to 67 of WO 2009 / 068444.

[0311] h.1) Distillation of menthol

[0312] To ensure the highest quality standards, especially regarding the sensory, particularly olfactory, characteristics of the resulting menthol, the method according to the invention, in the context of the preferred embodiment, includes, as an additional optional step h.1), distillation purification of racemic and / or optically active menthol, preferably by means of a partition column.

[0313] In a particularly preferred embodiment, the present invention also relates to a method for producing optically active menthol, comprising the following steps:

[0314] d.2) Asymmetric catalytic hydrogenation of nerol and / or geraniol to obtain optically active citronellol.

[0315] e.2) Cyclize the optically active citronellol obtained according to step d.2) in the presence of an acidic catalyst to obtain optically active isopreneol.

[0316] f.2) Purification of the optically active isoprene obtained according to step e.2), preferably by crystallization, and

[0317] g.2) Catalytically hydrogenate the optically active isomenthol obtained according to either step e.2) or f.2) to obtain optically active menthol.

[0318] According to step d.2), the asymmetric hydrogenation of neraldehyde is carried out. Preferably, the asymmetric catalytic hydrogenation of pure or enriched neraldehyde as described above under step d). In this manner, if desired, depending on the configuration of the asymmetric catalytic hydrogenation, optically active citronellol in the form of one of the two enantiomers, preferably in the form of D-citronellol, is available.

[0319] The optically active citronellol obtained according to step d.2) can then be cyclized according to step e.2) in the presence of an acidic catalyst to obtain the optically active isopreneol. Suitable acidic catalysts that may be mentioned are the acidic or Lewis acidic catalysts described above in step d.1), such as diarylphenoxyaluminum compounds.

[0320] In the context of this preferred embodiment, according to step f.2), the optically active isoprene obtained in this manner is purified by crystallization. Crystallization from the melt is preferably performed as described below in step f.1). In the context of this preferred embodiment of the method according to the invention, purified L-isomenthol is obtained.

[0321] Within the context of this embodiment of the method according to the invention, according to step g.2), the optically active isoprene obtained in this manner is then catalytically hydrogenated to obtain optically active menthol. The catalytic hydrogenation of isoprene to menthol is known to those skilled in the art and can be carried out using a wide variety of conventional heterogeneous hydrogenation catalysts. It has proven advantageous to carry out the catalytic hydrogenation in the presence of nickel-containing, copper-containing, zirconium-containing, and molybdenum-containing catalysts described above in step g.1).

[0322] A particular advantage of the method according to the invention should be emphasized is that it opens up a route to obtain optically active, preferably practically enantiomerically and diastereomerically pure L-menthol. The higher content of nerol in the asymmetric hydrogenation leads to a higher enantiomeric excess in the resulting optically active citronellol.

[0323] Furthermore, neraldehyde or geranialdehyde, especially geranialdehyde, obtained by the method according to the present invention can be used to produce linalool.

[0324] Another embodiment of the present invention relates to a method for producing linalool and includes additional steps d') and e'):

[0325] d') Catalytically hydrogenate geranialdehyde and / or neraldehyde obtained by the method of the present invention, preferably geranialdehyde obtained by the method of the present invention, especially geranialdehyde obtained in any one of steps 0), a), and / or b) (e.g., 0) and / or b), or a) and / or b)), particularly catalytically hydrogenate geranialdehyde obtained in any one of steps 0), a), and / or b) (e.g., 0) and / or b), or a) and / or b)) in the presence of a supported ruthenium, rhodium, osmium, iridium, or platinum catalyst, preferably a ruthenium catalyst supported on carbon black; to obtain geraniol; and

[0326] e') Isomerize geraniol in the presence of a catalyst, especially a tungsten catalyst, and very especially a dioxotungsten (VI) complex, to obtain linalool.

[0327] Linalool can be prepared by catalytic hydrogenation of geranialdehyde, which includes geranialdehyde, to obtain geraniol and then isomerizing it to linalool.

[0328]

[0329] The hydrogenation of geranialdehyde to obtain geraniol can be achieved by hydrogenation in the presence of a supported ruthenium, rhodium, osmium, iridium, or platinum catalyst (preferably a ruthenium catalyst supported on carbon black, or a ruthenium / iron catalyst supported on carbon, comprising 0.1% to 10% ruthenium and 0.1% to 5% iron by weight). See EP 1318128A2 and WO 2017 / 060243.

[0330] Crude mixtures of geraniol can be separated by distillation (see DE 10223974) or used for the isomerization of geraniol to linalool without purification.

[0331] Isomerization of geraniol to obtain linalool can be achieved via a tungsten catalyst, particularly a dioxotungsten (VI) complex, very especially of the general formula. (III) isomerization is achieved in the presence of a dioxotungsten (VI) complex, wherein L1 and L2 are ligands independently selected from the group consisting of amino alcohols, aminophenols, and mixtures thereof; and m and n are each 1 or 2. Further details regarding the isomerization of geraniol can be found in WO 03 / 048091 and WO 03 / 047749.

[0332] Additional catalysts that can be used for isomerization are described, for example, in CN 105218312B and CN 111087343B.

[0333] Therefore, one aspect of the present invention is an improved method for preparing linalool. Linalool can be prepared as described herein or by other methods known in the art.

[0334] Another aspect of the invention relates to linalool that can be obtained (or acquired) by the method of the invention.

[0335] It should be understood that the definitions and preferred embodiments set forth in the context of the methods described above and the available (or obtained) products are adapted, with necessary modifications, to the preparation and product characteristics of linalool. It should be understood that the available (or obtained) linalool possesses certain characteristics.

[0336] Another aspect of the present invention relates to a method for preparing vitamin A or vitamin A acetate, comprising the following steps:

[0337] - Citral having a nerol:geranium mass ratio as available (or obtained) according to the present invention, preferably having a nerol:geranium mass ratio of < 1, preferably < 0.75, is converted into pseudoionone;

[0338] - To obtain by reacting pseudoionone -Ionone,

[0339] - Will -Ionone (IX) is converted into -Vinyl ionoyl alcohol,

[0340] - make -Vinyl ionol phosphorylation to obtain C15-salt, and

[0341] - React the C15 salt with the C5 acetate to obtain vitamin A acetate.

[0342] Another aspect of the invention relates to vitamin A that can be obtained (or acquired) by the method of the invention.

[0343] It should be understood that the definitions and preferred embodiments set forth in the context of the methods described above and the available (or obtained) products, with necessary modifications, are applicable to the preparation and product characteristics of vitamin A and vitamin A acetate. It should be understood that the available (or obtained) vitamin A and vitamin A acetate have certain characteristics.

[0344] The following examples are used to illustrate the present invention and are not intended to limit the invention in any way.

[0345] Example

[0346] Example 1

[0347] General Program

[0348] Weigh the sensitizer (as indicated) into a borosilicate glass ampoule and seal it. Evacuate the ampoule via a cannula and fill it with argon. Repeat this procedure several times. Add a solution of geranialdehyde / nerol in acetonitrile (as indicated (ACN)) via a syringe. Irradiate the prepared ampoule at 20°C for the specified time, wavelength, and radiation power. Then analyze the reaction mixture by gas chromatography-flame ionization detector. The values ​​given are GC area percentages (solvent-free).

[0349] GC methods:

[0350] Agilent 6890N gas chromatograph with SSL-injector and FID

[0351] Column: CP-Sil 5 CB; 50 mx 0.25 mm x 0.12 µm

[0352] Carrier gas: Hydrogen

[0353] Carrier gas flow rate: 12.0 Psi; constant pressure

[0354] Injector temperature: 250°C

[0355] Flow split ratio: 1:100

[0356] Injection volume: 1.0 µL

[0357] Detector: FID

[0358] Detector temperature: 300°C

[0359] Column box procedure:

[0360]

[0361] Runtime: 20.0 min

[0362] Examples 1 to 5 - Photochemical Isomerization of Geranialdehyde

[0363]

[0364] 1) Radiative flux (365 nm): 0.21 W; Radiative flux (405 nm): 0.77 W.

[0365] 2) [Ir(dtbbpy)(ppy)2]PF6.

[0366] 3) Miskelone (4,4′-bis(dimethylamino)-benzophenone).

[0367] 4) 2CzPN (4,5-bis(carbazole-9-yl)-1,2-dicyanophenyl).

[0368] Examples 1 through 5 show that the geranialdehyde content of the mixture can be changed from 96 a% to approximately 50 a% through photochemical isomerization. Excess neraldehyde can be obtained by extending the irradiation time. See Example 13.

[0369] Examples 6 to 9 - Photochemical Isomerization of Neraldehyde

[0370]

[0371] 1)Radiative flux (365 nm): 0.21 W; Radiative flux (405 nm): 0.77 W.

[0372] 2) [Ir(dtbbpy)(ppy)2]PF6.

[0373] 4) 2CzPN (4,5-bis(carbazole-9-yl)-1,2-dicyanophenyl).

[0374] 5) Diacetyl (2,3-butanedione)

[0375] 6) a% = (peak) area.

[0376] Examples 6 to 9 show that the nerol content of the mixture can be changed from 99 a% to about 60 a% through photochemical isomerization.

[0377] Examples 10 to 12 - Photochemical isomerization of 100 mg geranialdehyde or neraldehyde in 2.5 ml ACN without a photocatalyst

[0378]

[0379] 1) Radiative flux (365 nm): 0.21 W; Radiative flux (405 nm): 0.77 W.

[0380] 7) Composition: 99.0% neraldehyde and 0.24% geranialdehyde and 0.76% byproducts (determined by GC).

[0381] 8) Composition: 3.5% neraldehyde and 96.2% geraniol and 0.3% byproducts (determined by GC).

[0382] It is evident from Examples 10 to 12 that, given sufficient reaction time, an excess of neraldehyde can be obtained regardless of the starting materials and wavelength.

[0383] Example 13

[0384] A 150 ml reaction flask made of borosilicate was evacuated several times and filled with argon. Nearly pure geranialdehyde (26.8 g, 169.3 mmol geranialdehyde and 6.1 mmol neraldehyde) was added, and the flask was irradiated at 20°C with a 365 nm LED (10 W radiant flux) for 5 h. Samples were taken periodically and analyzed by... 1 The reaction mixture was measured by 1H-NMR spectroscopy. The molar ratio of geranialdehyde and neraldehyde is provided in the table below.

[0385] 1 ¹H-NMR (500 MHz), Bruker, 298 K. Spectra were measured without field lock, without the addition of deuterated solvent and tetramethylsilane. Quantification was performed by normalizing the aldehyde signals of neraldehyde and geranialdehyde to the sum of their signals in the first spectrum recorded at 0 h. Since chemical shift references were not available according to IUPAC, the aldehyde signal of geranialdehyde was identified as a high-intensity doublet (J = 8 Hz) at the lowest field shift. The aldehyde signal of neraldehyde was identified as a low-intensity doublet (J = 8 Hz) at the high field shift to the signal of geranialdehyde.

[0386]

[0387] Example 14

[0388] Example 14 was repeated, except that the reaction mixture was analyzed by quantitative GC.

[0389]

[0390] Examples 13 and 14 show that in a mixture of neraldehyde and geranialdehyde obtained by light irradiation, the amount of neraldehyde is higher than that of geranialdehyde. This fact is advantageous for the production of neraldehyde.

Claims

1. A process comprising isomerizing neral of the formula (II) to geranial of the formula (I) or isomerizing geranial to neral, characterized in that (a) the isomerization is accomplished by irradiation with light.

2. The process according to claim 1, which is a process for the preparation of enriched or pure neral, comprising the following steps: a) isomerization of the enriched or pure geranial to a mixture of neral and geranial by irradiation with light; b) separation, in particular distillative separation, of the mixture comprising geranial and neral obtained in step a) to yield products, enriched or pure neral and enriched or pure geranial; and c) optionally recycling of the enriched or pure geranial obtained in step b) to step a).

3. The process according to claim 2, which additionally comprises as step 0) providing enriched or pure geranial by distillative separation of a mixture comprising geranial and neral.

4. The process according to claim 1, which is a process for the preparation of enriched or pure geranial, comprising the following steps: a) isomerization of the enriched or pure neral to a mixture of neral and geranial by irradiation with light; b) separation, in particular distillative separation, of the mixture comprising geranial and neral obtained in step a) to yield products, enriched or pure neral and enriched or pure geranial; and c) optionally recycling of the enriched or pure neral obtained in step b) to step a).

5. The process according to claim 4, which additionally comprises as step 0) providing enriched or pure neral by distillative separation of a mixture comprising geranial and neral.

6. The method of any one of claims 1 to 3, wherein, irradiation of the geranial in solution in a solvent in step a), or the process according to any one of claims 1, 4, or 5, wherein the geranial in solution in a solvent is irradiated with light in step a), wherein the solvent is preferably selected from the group consisting of water, dichloromethane, trichloromethane, tetrachloromethane, CS2, C1-C4 alcohols, chlorobenzene, fluorobenzene, trifluoromethylbenzene, acetonitrile, dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), ethyl acetate, acetone, and mixtures thereof.

7. The method of any one of claims 1 to 3, or 6, wherein, irradiation of the geranial in the presence of a sensitizer with light, in particular monochromatic light, in step a), or the process according to any one of claims 1, 4, 5, or 6, wherein the geranial is irradiated with light, in particular monochromatic light, in the presence of a sensitizer in step a).

8. The method of claim 7, wherein, The sensitizer is selected from [Ir(dF(CF3)ppy)2(bpy)]PF6, (Ir[dF(CF3)ppy]2(dtbbpy))PF6, (Ir[dF(CF3)ppy]2(dtbpy))PF6, (Ir[dF(Me)ppy]2(dtbbpy))PF6, [Ir(dtbbpy)(ppy)2]PF6, Ir(ppy)3, Ru(bpy)3Cl3, [Ru(bpy) 3] benzophenone, thioxanthone-9-one, Michler's ketone, tetramethoxy-anthracene-9-one, diacetyl-4,5-bis(carbazol-9-yl)-1,2-dicyanobenzene (2CzPN), 3,4,5,6-tetra(9H-carbazol-9-yl)phthalonitrile (4CzPN), 1,2,3,5-tetra(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), 4-methoxythioxanthone (4-MeOTX), 3-methoxythioxanthone (3-MeOTX), 2-methoxythioxanthone (2-MeOTX), 3-fluorothioxanthone (3-FTX), 2-fluorothioxanthone (2-FTX), 3,6-dimethoxythioxanthone (3,3'-MeOTX), 3,6-difluorothioxanthone (3,3'-FTX), 2-methoxy, 7-fluorothioxanthone (2-F,2'-MeOTX), 2,7-dimethoxythioxanthone (2,2'-MeOTX), and 9-cumyl-10-methylphenazyl tetrafluoroborate, 9-cumyl-10-methylphenazyl perchlorate, eosin Y, eosin B, 9,10-diphenylanthracene, 9,10-dicyanoanthracene, rose Bengal, and mixtures thereof.

9. The method of any one of claims 1 to 8, wherein, irradiation of the geranial with light, in particular monochromatic light, in the wavelength range of 350 to 490 nm in step a); or irradiation of the geranial with light, in particular monochromatic light, in the wavelength range of 350 to 490 nm in step a), wherein preferably at least 90% and at most 100% of the radiant flux of the light, in particular monochromatic light, is emitted in the range of 350 nm to 490 nm, and its monomodal emission spectrum exhibits a half-width of not more than + / - 100 nm, preferably not more than + / - 60 nm, such as + / - 10 to + / - 30 nm, with respect to the wavelength of the emission peak, and / or wherein preferably, according to any one of claims 7 or 8, the geranial and / or the neral is irradiated in the presence of a sensitizing agent.

10. The method of any one of claims 1 to 3, wherein, in step a) with light, in particular monochromatic light, the neral in pure form is irradiated, or according to any one of claims 1, 4 and 5, wherein in step a) with light, in particular monochromatic light, the mixture comprising or consisting of neral and geranial in pure form is irradiated.

11. The method of any one of claims 1-8 or 10, wherein, in step a) with light, in particular monochromatic light, the geranial is irradiated in the wavelength range of 300 to 420 nm; or in step a) with light, in particular monochromatic light, the neral is irradiated in the wavelength range of 300 to 420 nm; in step a) with light, in particular monochromatic light, the mixture comprising or consisting of neral and geranial in pure form is irradiated, wherein preferably at least 90% and at most 100% of the radiant flux of the light, in particular monochromatic light, is emitted in the range from 300 nm to 420 nm and its monomodal emission spectrum exhibits a half-width of not more than + / - 100 nm, preferably not more than + / - 60 nm, such as + / - 10 to + / - 30 nm, relative to the wavelength of the emission peak, and / or wherein preferably, according to claim 10, the geranial in pure form, the neral in pure form or the mixture comprising or consisting of neral and geranial in pure form is irradiated with light, in particular monochromatic light.

12. The method of any one of claims 1 to 11, wherein, Step a) is carried out in the temperature range of -20 °C to 100 °C.

13. The method of any one of claims 1 to 12, wherein, Step a) is carried out in the pressure range of 1 mbar to 20 bar.

14. The method of any one of claims 1 to 13, wherein, Step a) is carried out in a continuously stirred tank reactor, in a pumping loop, or in a continuous flow reactor.

15. The method of any one of claims 1 to 14, wherein, The irradiation with light is accomplished by using at least one LED (light emitting diode), or a laser.

16. The method of any one of claims 1-3 or 6-15, wherein, in step a) with monochromatic light, the geranial is irradiated.

17. The method of any one of claims 1 or 4-15, wherein, in step a) with monochromatic light, the neral is irradiated.

18. The method of any one of claims 1 to 17, wherein, The method is a method for producing the desired isomer, in particular the neral or the geranial, optionally contained in a mixture comprising neral and geranial.

19. The method of any one of claims 1 to 18, wherein, The method is a method for isomerizing geranial to neral or for isomerizing neral to geranial.

20. The method of any one of claims 1 to 19, wherein, The method is a method for preparing enriched or pure neral.

21. The method according to any one of claims 1, 6 to 16, or 18 to 20, which is a method for increasing the content of neral, in particular in a mixture comprising neral and geranial, comprising the step a) isomerizing the enriched or pure geranial to a mixture of neral and geranial by irradiation with light.

22. The method according to any one of claims 1, 6 to 16, or 18 to 21, which is a method for preparing enriched or pure neral, comprising the step a) isomerizing the enriched or pure geranial to a mixture of neral and geranial by irradiation with light.

23. The method according to any one of claims 21 or 22, additionally comprising as step 0) providing enriched or pure geranial by distillative separation of a mixture comprising geranial and neral.

24. The method according to any one of claims 1, 6-15, or 17-20, which is a method for increasing the content of geranial in a composition, in particular in a mixture comprising geranial and neral, comprising the following steps a) isomerizing the enriched or pure neral to a mixture of neral and geranial by irradiation with light.

25. The method according to any one of claims 1, 6-15, 17-20, or 24, which is a method for preparing enriched or pure geranial, comprising the following steps a) isomerizing the enriched or pure neral to a mixture of neral and geranial by irradiation with light.

26. The method according to any one of claims 24 or 25, additionally comprising as step 0) providing enriched or pure neral by distillative separation of a mixture comprising geranial and neral.

27. The method according to any one of claims 1 -3, 6-16, 18-23, which is a method for the production of menthol and comprises the additional steps d.1 ) to g.1 ): d.1 ) catalytic hydrogenation of neral obtained by the method according to any one of claims 1 -3, 6-16, 18-23, preferably the neral obtained in any one of steps 0), a) and / or b), to obtain citronellal, e.1 ) cyclization of citronellal in the presence of an acidic catalyst to obtain isopulegol, f.1 ) optional purification of isopulegol, preferably by crystallization, and g.1 ) catalytic hydrogenation of isopulegol to obtain menthol.

28. The method according to claim 27, comprising the additional steps d.2) to g.2): d.2) asymmetric catalytic hydrogenation of neral obtained by the method according to any one of claims 1 -3, 6-16, 18-23, preferably the neral obtained in any one of steps 0), a) and / or b), to obtain optically active citronellal, e.2) cyclization of optically active citronellal in the presence of an acidic catalyst to obtain optically active isopulegol, f.2) optional purification of optically active isopulegol, preferably by crystallization, and g.2) catalytic hydrogenation of optically active isopulegol to obtain optically active menthol.

29. The method according to any one of claims 1 to 26, preferably any one of claims 1, 4-15, 17-19, or 24-26, which is a method for the production of linalool and comprises the additional steps d’) and e’): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ d') catalytic hydrogenation of geranial and / or neral obtained by the process according to any one of claims 1 to 26, in particular geranial according to any one of claims 1, 4-15, 17-19, or 24-26, preferably the geranial obtained in any one of steps 0), a) and / or b), especially in the presence of a supported ruthenium, rhodium, osmium, iridium or platinum catalyst, preferably a ruthenium catalyst supported on carbon black; to obtain geraniol; and e') isomerization of geraniol in the presence of a catalyst, especially a tungsten catalyst, very especially a dioxotungsten(VI) complex to obtain linalool.

30. A mixture comprising neral and geranial obtainable from the process according to any one of claims 1 to 26.

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