Regeneration of triphenylphosphine oxides

Abstract

The present invention relates to an improved process for preparing triphenylphosphine (TPP) by reacting triphenylphosphine oxide (TPPO) with a catalyst in the presence of an inert solvent and adding a specific alcohol.

Description

[0001] The present invention relates to an improved method for preparing triphenylphosphine (TPP), which is achieved by reacting triphenylphosphine oxide (TPPO) with a specific alcohol added in the presence of an inert solvent using a catalyst.

[0002] TPP is a compound of formula (I)

[0003]

[0004] It is used in the industrial-scale Wittig Ylide synthesis for preparing olefin compounds such as vitamin A or carotenoids, where TPP is used in a stoichiometric amount and is oxidized to TPPO, i.e., a compound of formula (II).

[0005]

[0006] Therefore, a large amount of TPPO is generated during these reactions. Unfortunately, there is little disclosure about the uses of TPPO. Since TPPO is an extremely stable substance and very difficult to handle, attempts have been made to reconvert it into TPP.

[0007] A common method for dealing with the TPPO problem is to incinerate TPPO, so that it can be safely wasted. Thus, phosphorus can be reused without having to be purchased again.

[0008] Another method is to recycle TPPO into TPP and then reuse it.

[0009] This recycling method is known in the prior art (for example, known from EP638580 or "Heteroatom Chemistry" 26(3), 2015, pages 199 - 205).

[0010] Most of these recycling methods are carried out in the presence of polymethylhydrosiloxane (PMHS), which is a compound of formula (III) and is used in combination with a titanium compound as a catalyst

[0011] (CH3)3Si-(CH3(H)Si-O) n -Si(CH3)3(III)

[0012] where n is generally a value between 10 and 100000 (preferably n is a value between 100 - 20000, more preferably n is a value between 1000 - 12000, and most preferably n is a value between 1000 - 10000).

[0013] Berthod et al. described in "SYNLETT" 2007, issue 10, pages 1545 - 1548 a specific method for reducing triphenylphosphine oxide (TPPO) to regenerate triphenylphosphine (TPP) using hydrosiloxanes such as TMDS and PMHS in the presence of a titanium or zirconium compound as a catalyst. Berthod et al. pointed out that due to gel formation, PMHS is not conducive to work-up and recovery, while TMDS has higher reactivity. In addition, Berthod et al. also reported that when using a zirconium-based catalyst, no significant reduction of TPPO to TPP was observed.

[0014] However, using PMHS as a reducing agent has some major drawbacks, namely that a work-up step is required. This work-up step is usually carried out at a very high pH to hydrolyze the unreacted PMHS. Therefore, the work-up step consumes a large amount of base, such as KOH or NaOH (usually more than 10 equivalents), thus generating more wastewater.

[0015] Given the importance of the reaction that leads to the production of TPPO (as a by-product) and the problems associated with the use and handling of TPPO, there is a need for an improved method to convert TPPO to TPP for reuse and to minimize the generation of wastewater.

[0016] Surprisingly, it has been found that under specific reaction conditions, TPPO can be directly reduced to TPP in extremely high yields, and the work-up of the reaction mixture is carried out in an improved manner.

[0017] Therefore, the present invention relates to a method (P) for producing triphenylphosphine (the compound of formula (I)),

[0018]

[0019] wherein, in the first step (step 1), triphenylphosphine oxide (the compound of formula (II))

[0020]

[0021] is reacted with a compound of formula (III):

[0022] (CH3)3Si - O - (CH3(H)Si - O) n -Si(CH3)3 (III)

[0023] wherein,

[0024] n is a value between 10 and 100000 (more preferably, the value of n is 100 - 20000, more preferably, the value of n is 1000 - 12000, and most preferably, the value of n is 1000 - 10000)

[0025] React in the presence of at least one catalyst of formula (IV),

[0026]

[0027] wherein,

[0028] M is titanium (Ti), or zirconium (Zr), or a mixture of a compound (IV) where M is Ti and a compound (IV) where M is Zr, and

[0029] R, R1, R2 and R3 are each independently OR4, where R4 is a straight-chain or branched C1–C6 alkyl group,

[0030] The reaction is carried out in at least one aromatic solvent and / or at least one alkane at an elevated temperature: and

[0031] In a second step (step 2),

[0032] Add at least one alcohol of formula (V) to the reaction mixture:

[0033] R5-OH (V),

[0034] R5-OH (V),

[0035] where R5 is a straight-chain or branched C1–C6 alkyl group.

[0036] At the end of the process, the solvent (or solvent mixture) is removed (e.g., by distillation) to obtain the compound of formula (I).

[0037] The compound of formula (I) can be further purified by conventional methods.

[0038] Typically, the resulting compound of formula (I) is washed with the same alcohol (or a mixture thereof) as in formula (V) in step 2.

[0039] The solvents used in the present invention are at least one aromatic solvent and / or at least one alkane.

[0040] Suitable and preferred aromatic solvents are benzene, benzene substituted with one or more C1-C4 alkyl groups or benzene substituted with one or more OC1-C4 alkyl groups, or mixtures thereof.

[0041] More preferred aromatic solvents are benzene, toluene, mesitylene, xylene and anisole, in addition, the pure isomeric forms of diethylbenzene, or as a mixture of its ortho, meta and para isomers, and the solvent naphtha (also known as petroleum), such as Solvesso 100 from ExxonMobil, or mixtures thereof.

[0042] Accordingly, the present invention also relates to a method (P1), which is the method (P), wherein at least one aromatic solvent is selected from the group consisting of benzene, benzene substituted with one or more C1-C4 alkyl groups, and benzene substituted with one or more OC1-C4 alkyl groups.

[0043] Accordingly, the present invention also relates to a method (P1’), which is the method (P), wherein at least one aromatic solvent is selected from benzene, toluene, mesitylene, xylene, diethylbenzene (pure or a mixture of isomers), and anisole, or a mixture thereof.

[0044] Suitable alkanes are C4-C 18 alkanes, which can be straight-chain, branched-chain, and cyclic.

[0045] Suitable alkanes are pentane, hexane, heptane, octane, decane, undecane, dodecane, or any mixture of alkanes (such as Isopar M).

[0046] Accordingly, the present invention also relates to a method (P2), which is the method (P), wherein at least one alkane is a C4-C 18 alkane, which can be straight-chain, branched-chain, or cyclic.

[0047] Accordingly, the present invention also relates to a method (P2’), which is the method (P), wherein at least one alkane is selected from the group consisting of pentane, hexane, heptane, octane, decane, undecane, dodecane, and any mixture of alkanes.

[0048] At the start of the method according to the present invention, TPPO is suspended in at least one aromatic solvent and / or at least one alkane, and PMHS (the compound of formula (III)) is added.

[0049] The amount of PMHS added is generally and preferably 1.0 to 4 molar equivalents (calculated based on the amount of active hydrogen in PMHS relative to the amount of TPPO).

[0050] Accordingly, the present invention also relates to a method (P3), which is the method (P), (P1), (P1’), (P2), or (P2’), wherein the amount of the compound of formula (III) added is 1.0 to 4 molar equivalents (calculated based on the amount of active hydrogen in PMHS relative to the amount of TPPO).

[0051] The method in the present invention is carried out in the presence of at least one catalyst (the compound of formula (IV)). In the compound of formula (IV), M represents a metal of Group 4 of the periodic table, preferably titanium (Ti) or zirconium (Zr).

[0052] In another embodiment of the present invention, the method is carried out in the presence of a catalyst which is a mixture of a compound (IV)-Ti in which M is Ti in formula (IV) and a compound (IV)-Zr in which M is Zr in formula (IV).

[0053] In this embodiment, the mixture of compound (IV)-Ti and compound (IV)-Zr can be used in a ratio of (IV)-Ti:(IV)-Zr between 1:99 and 99:1, preferably between 20:80 and 80:20, or most preferably between 40:60 and 60:40.

[0054]

[0055] In the compound of formula (IV),

[0056] preferably, R, R1, R2 and R3 are each independently OR4,

[0057] wherein R4 is a straight-chain or branched C1-C6 alkyl group, more preferably R4 is a straight-chain or branched C1-C6 alkyl group, and most preferably R4 is a straight-chain or branched C2-C5 alkyl group.

[0058] Even more preferably, R4 is ethyl, isopropyl, n-propyl, isobutyl or n-butyl.

[0059] Accordingly, the present invention also relates to a method (P4) which is method (P), (P1), (P1’), (P2), (P2’) or (P3), wherein in the compound of formula (IV), R4 is a straight-chain or branched C2-C6 alkyl group.

[0060] Accordingly, the present invention also relates to a method (P4’) which is method (P), (P1), (P1’), (P2), (P2’) or (P3), wherein in the compound of formula (IV), R4 is a straight-chain or branched C2-C5 alkyl group.

[0061] Accordingly, the present invention also relates to a method (P4”) which is method (P), (P1), (P1’), (P2), (P2’) or (P3), wherein in the compound of formula (IV), R4 is selected from the group consisting of ethyl, isopropyl, n-propyl, isobutyl and n-butyl.

[0062] In the compound of formula (IV), R, R1, R2, R3 and R4 can be the same substituents, but they can also be different from each other.

[0063] Preferably, R, R1, R2, R3 and R4 have the same meaning.

[0064] In the method of the present invention, the catalyst, which is a compound of formula (IV), is generally and preferably used in an amount of 1-20 mol% (relative to the amount of TPPO), more preferably 1-15 mol%, and most preferably 6-14 mol%.

[0065] In a preferred embodiment, the method is carried out when the catalyst is a mixture of compound (IV)-Ti and (IV)-Zr. Generally, the amount of each compound used is 1-20 mol%, preferably 1-15 mol%, more preferably 1-12 mol%, and most preferably 1-10 mol% (relative to the amount of TPPO).

[0066] Here, the amount of compound (IV) as a mixture of (IV)-Ti and (IV)-Zr is used in a ratio of (IV)-Ti:(IV)-Zr between 3:1 and 1:3, preferably between 3:2 and 2:3, and most preferably 1:1. The typical amount of compound (IV)-Ti used is 1-10 mol%, and the typical amount of compound (IV)-Zr used is 1-10 mol%. More preferably, the typical amount of compound (IV)-Ti used is 1-5 mol%, and the typical amount of compound (IV)-Zr used is 1-5 mol%.

[0067] In another embodiment of the present invention, the method as described above is carried out in the presence of a catalyst. If the catalyst is a mixture of compound (IV)-Ti and compound (IV)-Zr, all 4 substituents R4 in the same compound (IV) are the same. Thus, compound (IV)-Ti may have 4 identical substituents, which may be the same as or different from the 4 identical substituents of compound (IV)-Zr. Preferably, the method as described above is carried out in the presence of a catalyst, wherein when using a mixture of compound (IV), R4 of compound (IV)-Ti is different from R4 of compound (IV)-Zr. For example, in such a mixture, compound (IV)-Ti may contain iPr as R4, while compound (IV)-Zr may contain nBu as the R4 substituent.

[0068] According to the present invention, in step 1, the compound of formula (IV) is generally and preferably used in the form of a solution of compound (IV) in a suitable solvent. Suitable solvents are selected from the group consisting of ethanol, isopropanol, n-propanol, isobutanol, and n-butanol. Preferably, the solvent corresponds to the substituent R4 used in the compound (IV). Preferably, the concentration of compound (IV) in the compound (IV) solution of the solvent is up to 100%, preferably 20 to 99% by weight concentration.

[0069] Accordingly, the present invention also relates to a method (P5), which is method (P), (P1), (P1'), (P2), (P2'), (P3), (P4), (P4'), (P4") or (P4'''), wherein the amount of the compound of formula (IV) used is 1-20 mol% (relative to the amount of TPPO), more preferably 1-15 mol%, and most preferably 6-14 mol%.

[0070] In the method according to the present invention, step 1 is carried out at an elevated temperature. Preferably, step 1 is carried out at a temperature of 100°C to 200°C, more preferably at a temperature of 150°C to 180°C.

[0071] Accordingly, the present invention also relates to a method (P6), which is method (P), (P1), (P1'), (P2), (P2'), (P3), (P4), (P4'), (P4"), (P4''') or (P5), wherein step 1 is carried out at a temperature of 100°C to 200°C.

[0072] Accordingly, the present invention also relates to a method (P6'), which is method (P), (P1), (P1'), (P2), (P2'), (P3), (P4), (P4'), (P4"), (P4''') or (P5), wherein step 1 is carried out at a temperature of 150°C to 180°C.

[0073] If the solvent (or solvent mixture) is a low-boiling solvent, step 1 is preferably carried out in an autoclave.

[0074] The reaction time of step 1 in the method according to the present invention is generally several hours. Generally and preferably, the reaction time of step 1 in the method according to the present invention is 3 to 10 hours.

[0075] Accordingly, the present invention also relates to a method (P7), which is method (P), (P1), (P1'), (P2), (P2'), (P3), (P4), (P4'), (P4"), (P4'''), (P5), (P6) or (P6'), wherein the reaction time of step 1 is 3 to 10 hours.

[0076] In a preferred embodiment, after step 1, the solvent or solvent mixture is completely or partially removed from the reaction mixture. This step (step 1a) can be carried out by common methods (such as distillation).

[0077] Accordingly, the present invention also relates to a method (P8), which is method (P), (P1), (P1'), (P2), (P2'), (P3), (P4), (P4'), (P4"), (P4'''), (P5), (P6), (P6') or (P7), wherein after step 1, the solvent or solvent mixture is (completely or partially) removed from the reaction mixture.

[0078] After step 1 (or step 1a), the reaction mixture is cooled to a temperature below 100 °C, usually to a temperature between 40 °C and 90 °C.

[0079] Accordingly, the present invention also relates to a method (P9), which is method (P), (P1), (P1’), (P2), (P2’), (P3), (P4), (P4’), (P4”), (P5), (P6), (P6’), (P7) or (P8), wherein after step 1 (or step 1a), the reaction mixture is cooled to a temperature below 100 °C.

[0080] Accordingly, the present invention also relates to a method (P9’), which is method (P), (P1), (P1’), (P2), (P2’), (P3), (P4), (P4’), (P4”), (P5), (P6), (P6’), (P7) or (P8), wherein after step 1 (or step 1a), the reaction mixture is cooled to a temperature between 40 °C and 90 °C.

[0081] In step 2 of the method according to the present invention (performed after step 1 or 1a), at least one alcohol of formula (V) is added to the reaction mixture:

[0082] R5-OH,

[0083] wherein R5 is a straight-chain or branched C1-C6 alkyl group.

[0084] Preferably, R5 is a straight-chain or branched C1-C4 alkyl group.

[0085] More preferably, at least one alcohol of formula (V) is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol. Most preferably, at least one alcohol of formula (V) is isopropanol.

[0086] Accordingly, the present invention also relates to a method (P10), which is method (P), (P1), (P1’), (P2), (P2’), (P3), (P4), (P4’), (P4”), (P5), (P6), (P6’), (P7), (P8), (P9) or (P9’), wherein the alcohol R5 of formula (V) is a straight-chain or branched C1-C4 alkyl group.

[0087] Accordingly, the present invention also relates to a method (P10'), which is method (P), (P1), (P1'), (P2), (P2'), (P3), (P4), (P4'), (P4"), (P5), (P6), (P6'), (P7), (P8), (P9) or (P9'), wherein the alcohol is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol, preferably isopropanol.

[0088] The alcohol of formula (V) is generally and preferably added to the reaction mixture in a molar excess (relative to TPPO). Generally, the amount of at least one alcohol added is at least 1 - 30 molar equivalents (relative to TPPO).

[0089] Accordingly, the present invention also relates to a method (P11), which is method (P), (P1), (P1'), (P2), (P2'), (P3), (P4), (P4'), (P4"), (P5), (P6), (P6'), (P7), (P8), (P9), (P9'), (P10) or (P10'), wherein at least one alcohol of formula (V) is added to the reaction mixture in a molar excess (relative to TPPO).

[0090] Accordingly, the present invention also relates to a method (P11'), which is method (P), (P1), (P1'), (P2), (P2'), (P3), (P4), (P4'), (P4"), (P5), (P6), (P6'), (P7), (P8), (P9), (P9'), (P10) or (P10'), wherein at least one alcohol of formula (V) is added to the reaction mixture in an amount of at least 1 - 30 molar equivalents (relative to TPPO).

[0091] Preferably, in step 2, the reaction mixture is heated to a temperature of 40°C to 90°C.

[0092] Accordingly, the present invention also relates to a method (P12), which is method (P), (P1), (P1'), (P2), (P2'), (P3), (P4), (P4'), (P4"), (P5), (P6), (P6'), (P7), (P8), (P9), (P9'), (P10), (P10'), (P11) or (P11'), wherein the reaction temperature in step 2 is between 40°C and 90°C.

[0093] Finally, the reaction mixture is cooled to a low temperature, generally between -10°C and 10°C.

[0094] Accordingly, the present invention also relates to a method (P13), which is method (P), (P1), (P1’), (P2), (P2’), (P3), (P4), (P4’), (P4”), (P5), (P6), (P6’), (P7), (P8), (P9), (P9’), (P10), (P10’), (P11), (P11’) or (P12), wherein at the end of the reaction in step 2, the reaction temperature is reduced to a temperature between -10°C and 10°C.

[0095] At this time, TPP will precipitate out and can be separated by filtration.

[0096] Generally, the obtained product (TPP) is washed with the same alcohol (or mixture of alcohols) of formula (V) as that added in step 2.

[0097] As an additional feature, the mother liquor obtained at the end of step 2 and after (optional) washing can be further processed.

[0098] The filter cake is washed with the same alcohol solvent used in the previous step.

[0099] In addition, we found that treating the mother liquor with aqueous ammonia (an aqueous solution of NH3) has some surprising and beneficial effects.

[0100] When ammonia water is added, the silicon-containing compound forms a solid precipitate, which also contains titanium from the catalyst and can be removed from the solution.

[0101] Through this unexpected discovery, almost all of the silicon and titanium can be removed from the aqueous alcohol solution.

[0102] Accordingly, the present invention also relates to a method (P14), which is method (P), (P1), (P1’), (P2), (P2’), (P3), (P4), (P4’), (P4”), (P5), (P6), (P6’), (P7), (P8), (P9), (P9’), (P10), (P10’), (P11), (P11’), (P12) or (P13), wherein in the third step (step 3), the mother liquor (obtained after step 2) is treated with ammonia water.

[0103] Generally and preferably, the mother liquor is treated with ammonia water, and the concentration of NH3 in H2O in the ammonia water is 1 - 30 weight percent (wt%), based on the total weight of the ammonia water.

[0104] Accordingly, the present invention also relates to a method (P15), which is method (P14), wherein the concentration of NH3 in H2O in the ammonia water is 1 - 30 weight percent (wt%), based on the total weight of the ammonia water.

[0105] The treatment of the mother liquor is carried out at a temperature of 40 °C to 120 °C, preferably at a temperature of 60 °C to 100 °C.

[0106] Accordingly, the present invention also relates to a method (P16), which is method (P14) or (P15), wherein step 3 is carried out at a temperature of 40 °C to 120 °C.

[0107] Accordingly, the present invention also relates to a method (P16'), which is method (P14) or (P15), wherein step 3 is carried out at a temperature of 60 °C to 100 °C.

[0108] Optionally, the treatment of the mother liquor can be carried out in the presence of at least one surfactant.

[0109] Suitable surfactants include cetyltrimethylammonium bromide, myristyltrimethylammonium bromide, dodecyltrimethylammonium bromide or cetyltrimethylammonium bromide.

[0110] Accordingly, the present invention also relates to a method (P17), which is method (P14), (P15), (P16) or (P16'), wherein step 3 is carried out in the presence of at least one surfactant.

[0111] Accordingly, the present invention also relates to a method (P17'), which is method (P14), (P15), (P16) or (P16'), wherein step 3 is carried out in the presence of at least one surfactant selected from the group consisting of cetyltrimethylammonium bromide, myristyltrimethylammonium bromide, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, cetyltrimethylammonium chloride, myristyltrimethylammonium chloride, dodecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride.

[0112] Optionally, tetraethyl orthosilicate can also be used in the treatment of the mother liquor.

[0113] Accordingly, the present invention also relates to a method (P18), which is method (P14), (P15), (P16), (P16'), (P17) or (P17'), wherein step 3 is carried out in the presence of tetraethyl orthosilicate.

[0114] In addition, the present invention relates to the use of TPP prepared by the above method to prepare carotenoids, which are selected from the group consisting of α-, β-, γ- or δ-carotene, apocarotenal, β-apocarotenal-8'-aldehyde, β-apocarotenal-12'-aldehyde, lycopene, bixin, or carotenoids including lutein, astaxanthin, canthaxanthin, citranaxanthin, cryptoxanthin, flavoxanthin, violaxanthin or zeaxanthin.

[0115] The present invention also relates to a method for preparing carotenoids, comprising the following steps:

[0116] i) preparing TPP from waste containing TPPO according to the above method,

[0117] ii) coupling the corresponding molecular building block compounds of carotenoids with the TPP prepared in step i) above as a coupling reagent, and

[0118] iii) recovering the corresponding carotenoids.

[0119] The coupling reaction as described above can be any reaction forming a C═C bond, preferably a Wittig reaction as described in DE954247. The molecular building block compounds in the present invention can have at least two structures, each independently being C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, and having at least one functional group suitable for such a coupling reaction.

[0120] The present invention also relates to carotenoids obtained by the above method, wherein the carotenoids are selected from the group of carotenes including α-, β-, γ- or δ-carotene, apocarotenal, β-apocarotenal-8'-aldehyde, β-apocarotenal-12'-aldehyde, lycopene, bixin, or the group of xanthophylls including lutein, astaxanthin, canthaxanthin, citranaxanthin, cryptoxanthin, flavoxanthin, violaxanthin or zeaxanthin.

[0121] The following examples illustrate the present invention. Examples

[0122] Example 1:

[0123] Load 70 g of TPPO into an autoclave and add 270 g of toluene. Add 37 g of PMHS and 7 g of Ti(OiPr)4. Close the autoclave and heat the reaction mixture to 170 °C and hold for 6 hours. After this time, cool the reaction mixture to 55 °C. Distill off the toluene (>90% of the initially used amount). Add 169 g of iPrOH (isopropyl alcohol) and maintain the reaction temperature at 55 °C until the solid dissolves. Cool the reaction mixture to 0 °C to crystallize TPP. Filter off the TPP and wash it with iPrOH. Finally, dry the TPP to obtain 55 g of product.

[0124] Example 2:

[0125] Load 70 g of TPPO into an autoclave and add 270 g of toluene. Add 32 g of PMHS and 5.5 g of Ti(OiPr)4. Close the autoclave and heat the reaction mixture to 170 °C and hold for 6 hours. After this time, cool the reaction mixture to 60 °C. Distill off the toluene (>90% of the initially used amount). Add 169 g of iPrOH and maintain the reaction temperature at 60 °C until the solid dissolves. Cool the reaction mixture to 2 °C to crystallize TPP. Filter off the TPP and wash it with iPrOH. Finally, dry the TPP to obtain 46 g of product.

[0126] Example 3:

[0127] Load 70 g of TPPO into an autoclave and add 270 g of toluene. Add 38 g of PMHS and 8.5 g of Ti(OnBu)4. Close the autoclave and heat the reaction mixture to 170 °C and hold for 6 hours. After this time, cool the reaction mixture to 57 °C. Distill off the toluene (>90% of the initially used amount). Add 168 g of iPrOH and maintain the reaction temperature at 65 °C until the solid dissolves. Cool the reaction mixture. Filter off the TPP and wash it with iPrOH. Finally, dry the TPP to obtain 55.5 g of product.

[0128] Example 4:

[0129] Load 70 g of TPPO into an autoclave. Add 360 g of toluene and 19 g of PMHS. Close the autoclave and heat the reaction mixture to 170 °C, and add 7.5 g of the catalyst Ti(OiPr)4 within 2 hours. After the addition is complete, cool the reaction mixture to 53 °C. Distill off the toluene (>90% of the initially used amount). Add 170 g of iPrOH and maintain the reaction temperature at 60 °C until the solid dissolves. Cool the reaction mixture to 0 °C to crystallize TPP. Filter off the TPP and wash it with iPrOH. Finally, dry the TPP to obtain 33.6 g of product.

[0130] Example 5:

[0131] 75 g of TPPO was charged into a reactor, and 375 g of mesitylene was added. 41 g of PMHS and 7.7 g of Ti(OiPr)4 were added. The reaction mixture was heated to 150 °C and maintained for 14 h. After this time, the reaction mixture was cooled to 90 °C. Mesitylene (>90% of the initially used amount) was removed by distillation. 180 g of iPrOH was added, and the reaction temperature was maintained at 60 °C until the solid dissolved. The reaction mixture was cooled to 0 °C to crystallize TPP. TPP was separated by filtration and washed with iPrOH. Finally, TPP was dried to give 55 g of product.

[0132] Example 6:

[0133] 235 g of TPPO waste containing 149.3 g of TPPO, methanol and water was charged into a 2 L double-jacketed glass reactor. 720 g of mesitylene was added to this brownish solution. 162 g of a methanol, water and mesitylene mixture (800 to 160 mbar, 60 °C to 90 °C) was distilled off until KF < 0.1%. 15.4 g of Ti(OiPr)4, 79.9 g of PMHS and 102 g of mesitylene were added to the suspension. The reaction mixture was heated to 170 °C and maintained for 12 h (slight reflux). After this time, the reaction mixture was cooled to 60 °C. The crude solution was added to a second 2 L double-jacketed glass reactor pre-charged with 181 g of 45% w / w KOH over 2 h. When the evolution of hydrogen stopped, stirring was stopped and two phases formed. 237 g of the aqueous phase was drained off. The organic phase was concentrated (50 to 10 mbar, 90 °C) to 142 g of an oily residue. 350 g of methanol was added, and stirring was continued at 60 °C for 1 h. The temperature was lowered to 0 °C over 2 h and the suspension was filtered. TPP was washed with 50 g of cold methanol and dried to give 117 g of product.

[0134] Example 7:

[0135] 118 g of TPPO waste containing 75 g of TPPO, methanol, and water was charged into a 2 L double-jacketed glass reactor. 360 g of mesitylene was added to the brownish solution. 81 g of a methanol, water, and mesitylene mixture (800 to 160 mbar, 60 °C to 90 °C) was distilled off until KF < 0.1%. 7.7 g of Ti(OiPr)4, 41 g of PMHS, and 51 g of mesitylene were added to the suspension. The reaction mixture was heated to 170 °C and maintained for 12 h (gentle reflux). After this time, the reaction mixture was cooled to 60 °C. The crude solution was added to a second 2 L double-jacketed glass reactor precharged with 100 g of 20% w / w KOH over 2 h. When hydrogen evolution ceased, stirring was stopped and two phases formed. 119 g of the aqueous phase was drained off. The organic phase was concentrated (50 to 10 mbar, 90 °C) to 71 g of an oily residue. 180 g of iPrOH was added and stirring was continued at 60 °C for 1 h. The temperature was lowered to 0 °C over 2 h and the suspension was filtered. The TPP was washed with 50 g of cold iPrOH and dried under vacuum to give 55 g of product.

[0136] Example 8:

[0137] 128 g of TPPO was charged into a 2 L double-jacketed glass reactor. 513 g of diethylbenzene (o,m,p-isomer mixture) was added to the yellow solution. 6.63 g of Ti(OiPr)4, 10.9 g of Zr(OnBu)4, and 67.9 g of PMHS were added to the suspension. The reaction mixture was heated to 170 °C and maintained for 8 h. After this time, the reaction mixture was cooled to 100 °C and the solvent was removed by distillation. The crude product was cooled to 50 °C, 350 g of iPrOH was added and stirring was continued until all solids had dissolved. The reaction mixture was cooled slowly and seeded. The temperature was further lowered to 0 °C and the product TPP was filtered off, washed with 50 g of cold iPrOH. The product was then dried under vacuum to give 98 g of TPP.

[0138] Example 9:

[0139] 128 g of TPPO was charged into a 2 L double-jacketed glass reactor. 509 g of Solvesso 100 (Petroleum, a solvent from ExxonMobil) was added to this yellow solution. 6.61 g of Ti(OiPr)4, 10.8 g of Zr(OnBu)4, and 67.8 g of PMHS were added to the suspension. The reaction mixture was heated to 170 °C and maintained for 6 h. After this time, the reaction mixture was cooled to 120 °C and the solvent was removed by distillation. The crude product was cooled to 50 °C, 350 g of iPrOH was added and stirred until all solids dissolved. The reaction mixture was cooled slowly and seeded. The temperature was further lowered to 0 °C and the product TPP was separated by filtration and washed with 50 g of cold iPrOH. Thereafter, the product was dried under vacuum to give 96 g of TPP.

[0140] Typical example of mother liquor treatment (Step 3):

[0141] 500 g of water and 100 g of 20% w / w NH4OH were added to a reactor. The mixture was heated to 80 °C and 100 g of the mother liquor from TPP filtration (Examples 1 - 5, 8, 9) was added over 90 min. The reaction mixture was stirred for 1 h. The white precipitate formed was separated by filtration and dried to give 18 g of product.

Claims

1. A method for preparing triphenylphosphine (a compound of formula (I)) wherein the first step (Step 1) is triphenylphosphine oxide (a compound of formula (II)) reacting with a compound of formula (III) (CH3)3Si-O-(CH3(H)Si-O) n -Si(CH3)3(III) wherein the value of n is between 10 and 100,000, in the presence of at least one catalyst of formula (IV), wherein M is titanium (Ti) or zirconium (Zr), or a mixture of both, and R, R1, R2 and R3 are each independently OR4, wherein R4 is a straight-chain or branched C1-C6 alkyl group, the reaction is carried out in at least one aromatic solvent and / or at least one alkane, at an elevated temperature; and in the second step (Step 2) adding at least one alcohol of formula (V) R5-OH (V) to the reaction mixture, wherein R5 is a straight-chain or branched C1–C6 alkyl group.

2. The method according to claim 1, wherein the at least one aromatic solvent is selected from the group consisting of benzene, benzene substituted with one or more C1-C4-alkyl groups and benzene substituted with one or more OC1-C4-alkyl groups, or a mixture thereof, or wherein the at least one alkane is a C4-C 18 alkane, which may be straight-chain, branched-chain or cyclic, or a mixture thereof.

3. The method according to any one of the preceding claims, wherein the catalyst in Step 1 is a mixture of a compound (IV) with M being titanium and a compound (IV) with M being zirconium.

4. The method according to claim 3, wherein the ratio of the compound (IV) with M being titanium to the compound (IV) with M being zirconium, (IV)-Ti:(IV)-Zr, is between 1:99 and 99:1, preferably between 20:80 and 80:20, and most preferably between 40:60 and 60:

40.

5. The method according to any one of the preceding claims, wherein the amount of the compound of formula (III) added is 1.0 to 4 molar equivalents (calculated based on the active hydrogen content of PMHS relative to the amount of TPPO).

6. The method according to any one of the preceding claims, wherein R4 in the compound of formula (IV) is a straight-chain or branched C1-C6-alkyl group, and preferably, R4 in the compound of formula (IV) is selected from the group consisting of ethyl, isopropyl, n-propyl, isobutyl and n-butyl.

7. The method according to any one of claims 3 to 6, wherein in the case of using a mixture of the compound (IV), R4 in the compound (IV)-Ti is different from R4 in the compound (IV)-Zr.

8. The method according to any one of the preceding claims, wherein the amount of the compound of formula (IV) used is 1-20 mol% (relative to the amount of TPPO).

9. The method according to any one of the preceding claims, wherein Step 1 is carried out at a temperature of 100°C to 200°C.

10. The method according to any one of the preceding claims, wherein after Step 1, the solvent or solvent mixture (in whole or in part) is removed from the reaction mixture, and in the alcohol of formula (V), R5 is a straight-chain or branched C1-C4-alkyl group, or preferably R5 is a branched C1-C6 alkyl group, or more preferably the alcohol of formula (V) is isopropanol (iPrOH).

11. The method according to any one of the preceding claims, wherein at least one alcohol of formula (V) is added to the reaction mixture in a molar excess (relative to TPPO).

12. The method according to any one of the preceding claims, wherein in the third step (step 3), the mother liquor obtained after step 2 is treated with ammonia water, and based on the total weight of the ammonia water, the concentration of NH3 in H2O of the ammonia water is preferably 1-30 wt%.

13. The method according to claim 12 or 13, wherein step 3 is carried out at a temperature of 40°C to 120°C, and step 3 is preferably carried out in the presence of at least one surfactant.

14. A method for preparing carotenoids, comprising the following steps: i) preparing TPP from waste containing TPPO according to any one of the preceding claims, ii) carrying out a coupling reaction on the molecular building block compound of the corresponding carotenoid using the TPP prepared in the above step i) as a coupling reagent, and iii) recovering the corresponding carotenoid.

15. Carotenoids obtained by the method according to claim 14.

16. Use of triphenylphosphine (TPP) prepared according to any one of the preceding claims in the preparation of carotenoids, wherein the carotenoids are selected from the group consisting of α-, β-, γ- or δ-carotene, apo-carotenal, β-apo-8'-carotenal, β-apo-12'-carotenal, lycopene, canthaxanthin, or the group consisting of lutein, astaxanthin, zeaxanthin, citranaxanthin, cryptoxanthin, flavoxanthin, violaxanthin or zeaxanthin.

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