Photooxidation of phenolic compounds

Abstract

The present invention relates to the photooxidation of phenolic compounds to their respective quinoid compounds using methylene blue as a photosensitizer in a solvent mixture of water and alcohol, using light in the high wavelength range of the visible spectrum.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to the preparation of quinoid compounds, in particular to the field of photooxidation of phenolic compounds.

[0002] [Background of the invention] Quinones are an important class of chemicals that may be of broad interest for the synthesis of molecules in the fields of pharmaceuticals, fragrance ingredients, food and feed additives, and colorants and dyes.

[0003] Murtinho D. et al., J. Chem. Soc. Perkin Trans. 2, 2000, 2441-2447, proposed the photooxidation of naphthalene-1,5-diol using oxygen in the presence of a photosensitizer to give 5-hydroxy-naphthohalene-1,4-dione. Specifically, they disclosed methylene blue as the photosensitizer in a mixture of acetonitrile and dichloromethane. However, due to the moderate yield, they suggested using a porphyrin-type photosensitizer instead.

[0004] McQuade DT et al. RSC Adv., 2016, 6, 12717-12725 discloses the photooxidation of various 1-naphthol derivatives to their respective 1,4-naphthoquinione derivatives using oxygen in the presence of a porphyrin-type photosensitizer in a mixture of acetonitrile and dichloromethane and a white LED as the light source in a flow reactor.

[0005] However, such porphyrin compounds as disclosed above are rather expensive and not readily commercially available, while acetonitrile and dichloromethane are solvents with significant ecological and ecotoxicological drawbacks.

[0006] G. Wurm et al., Arch. Pharm. 319, 97-101 (1986), disclose that when photooxidized, 2-alkyl-5-methoxynaphth-1-ols give low yields (<20%) of their respective 1,4-naphthoquinone derivatives. In particular, they disclose that 5-methoxy-2-(2-methylpropyl)-naphth-1-ol in methanol using methylene blue as a sensitizer gives less than 3% yield of the desired 2-isobutyl-5-methoxynaphthalene-1,4-dione.

[0007] Methylene blue is often used as a photosensitizer for photoreactions and is readily commercially available from a variety of sources.

[0008] [Summary of the Invention] The process of obtaining specific quinones of formula (I) from the respective phenolic compounds is of great interest since phenols are generally widely available and can be produced by known chemical transformations.

[0009] Surprisingly, it has been found that photo-oxidation as claimed in claim 1 provides an efficient way to solve this problem.

[0010] It has been found that this photooxidation of the compound of formula (II) gives the desired product (I) in very high conversion, yield and selectivity.

[0011] In the present invention, methylene blue can be used, which is a readily available, cost-effective, and highly attractive photosensitizer, to obtain the desired product not only in very high yield and conversion but also with very high selectivity. A particular advantage is that this process can be carried out in the absence of chlorinated solvents. Therefore, the above process is very attractive for industrial applications.

[0012] Further aspects of the invention are the subject matter of further independent claims. Particularly preferred embodiments are the subject matter of the dependent claims.

[0013] [Detailed Description of the Invention] The present invention provides a process for preparing a compound of formula (I) from a compound of formula (II) by photooxidation, comprising: [ka] (In the formula, R 1 and R 2 are, independently of each other, H or C 1~4 Alkyl or halogenated C 1~4 Alkyl group, OR 9 group or -CH2-OR 9 represents a group, R 3 and R 4 are, independently of each other, H or C 1~4 Alkyl or halogenated C 1~4 Alkyl group or OR 9 group or -CH2-OR 9 group, in particular H or CH3, or both of the formula [ka] forming a group of In the formula, R 5 and R 6 and R 7 are independently H or OH or C 1~4 Alkyl group or OR 9 represents a group, However, residue R 5 and R 6 and R 7 At least two of these are different from OH. The dotted line represents the bond through which the substituent of formula (I) is attached to the remainder of the compound of formula (II), R 9 is C 1~4 alkyl groups, especially CH3), Water and at least one C 1~8 Alkanol or at least one C 2~4 using oxygen and a photosensitizer of formula (III) in a solvent mixture with an alkylene diol [ka] (In the formula, R 8 , R 8’ , R 8’’ and R 8’’’ are, independently of each other, H or C 1~4 represents an alkyl group, Or, R 8 and R 8’ and / or R 8’’ and R 8’’’ forms a 5- or 6-membered ring together with N, X - represents an anion, however, R 1 =R 2 =R 3 =CH3, R 4 Unlike H, R 1 =R 2 =R 4 =CH3, R 3 Unlike H, residue R 1 ,R 2 ,R 3 and R 4 At least one of the following is different from H: residue R 8 ,R 8’ ,R 8’’ and R 8’’’ is different from H), and The spectrum has a peak wavelength (λ max The present invention relates to a process for producing a compound of formula (I) from a compound of formula (II) using light having a

[0014] For clarity, some terms used herein are defined as follows:

[0015] As used herein, "C x~y A "-alkyl" group is an alkyl group containing x to y carbon atoms, i.e., for example, C 1~3An alkyl group is an alkyl group containing 1 to 3 carbon atoms. The alkyl group may be straight or branched. For example, -CH(CH3)-CH2-CH3 is considered a C4-alkyl group.

[0016] Similarly, C x~y Alkanol, or C x~y An alkylenediol is an alcohol having one or two OH groups, where the alcohol has an alkyl or alkylene group containing x to y carbon atoms.

[0017] In this specification, when the same label for a symbol or group is present in multiple formulas, the definition of the group or symbol given in the context of one particular formula also applies to other formulas containing the same label.

[0018] The peak wavelength is the wavelength at which the spectrum reaches its maximum intensity.

[0019] In the aforementioned process, a compound of formula (II) is photo-oxidized to give a compound of formula (I). Compounds of formula (II) are readily available by synthesis known to those skilled in the art and / or are commercially available.

[0020] In one embodiment, R 3 and R 4 are, independently of each other, H or C 1~4 Alkyl or halogenated C 1~4 an alkyl group, preferably a CF3 group, or an OR 9 group, preferably an OCH group, or a -CH-OR group 9 group, preferably a -CH2-OCH3 group, in particular H or CH3.

[0021] However, R 1 =R 2 =R 3 =CH3, R 4 is different from H. Furthermore, R 1 =R 2 =R 4 =CH3, R 3is different from H. Furthermore, residue R 1 ,R 2 ,R 3 and R 4 At least one of is different from H.

[0022] In other words, the compound of formula (II) is neither 2,3,6-trimethylphenol nor 2,3,5-trimethylphenol nor phenol.

[0023] In this embodiment, the residue R 1 , R 2 , R 3 and R 4 At least one, preferably at least two of: OR 9 groups, especially methoxy groups.

[0024] The compound of formula (II) of this embodiment is preferably o-cresol, m-cresol, 2-methoxyphenol, 3-methoxyphenol, 2,3-dimethylphenol, 2,5-dimethylphenol, 2,6-dimethylphenol, 3,5-dimethylphenol, 2-methyl-3-methoxyphenol, 2-methyl-5-methoxyphenol, 2-methoxy-6-methylphenol, 2-methoxy-3-methylphenol, 3-methoxy-5-methylphenol, 2-methoxy-5-methylphenol, 2,3-dimethoxyphenol, 2,5-dimethoxyphenol. The phenol is selected from the group consisting of phenol, 3,5-dimethoxyphenol, 2,6-dimethoxyphenol, 2,3-dimethoxy-6-methylphenol, 2,3-dimethoxy-5-methylphenol, 2,5-dimethoxy-3-methylphenol, 2,6-dimethoxy-3-methylphenol, 3,5-dimethoxy-2-methylphenol, 2-ethoxyphenol, 3-ethoxyphenol, 2,3-diethoxyphenol, 2,5-diethoxyphenol, 2,6-diethoxyphenol, 3,5-diethoxyphenol and 5-isopropyl-2-methylphenol.

[0025] In another embodiment, R 3 and R 4 are both expressions [ka] (In the formula, R 5 and R 6 and R 7 are independently H or OH or C 1~4 Alkyl group or OR 9 represents a group, R 9 is C 1~4 alkyl groups, especially CH3; However, residue R 5 and R 6 and R 7 provided that at least two of are different from OH.

[0026] The compound of formula (II) of this embodiment is preferably 1-naphthol, 2-methylnaphthalen-1-ol, 3-methylnaphthalen-1-ol, 5-methylnaphthalen-1-ol, 6-methylnaphthalen-1-ol, 7-methylnaphthalen-1-ol, 8-methylnaphthalen-1-ol, 2,3-dimethylnaphthalen-1-ol, 2,5-dimethylnaphthalen-1-ol, 2,6-dimethylnaphthalen-1-ol, 2,7-dimethylnaphthalen-1-ol, 2,8-dimethylnaphthalen-1-ol, 3,5-dimethylnaphthalen-1-ol, 3,6-dimethylnaphthalen-1-ol, 3,7-dimethylnaphthalen-1-ol, 3,8-dimethylnaphthalen-1-ol, 5,6-dimethylnaphthalen-1-ol, 5,7-dimethylnaphthalen-1-ol, 5,8-dimethylnaphthalen-1-ol, 5,9-dimethylnaphthalen-1-ol, 6,10-dimethylnaphthalen-1-ol, 6,11-dimethylnaphthalen-1-ol, 6,12-dimethylnaphthalen-1-ol, 6,13-dimethylnaphthalen-1-ol, 6,14-dimethylnaphthalen-1-ol, 6,15-dimethylnaphthalen-1-ol, 6,16-dimethylnaphthalen-1-ol, 6,17-dimethylnaphthalen-1-ol, 6,18-dimethylnaphthalen-1-ol, 6,19 ... naphthalene-1-ol, 6,7-dimethylnaphthalene-1-ol, 6,8-dimethylnaphthalene-1-ol, 7,8-dimethylnaphthalene-1-ol, 2,3,5-trimethylnaphthalene-1-ol, 2,3,6-trimethylnaphthalene-1-ol, 2,3,7-trimethylnaphthalene-1-ol, 2,3,8-trimethylnaphthalene-1-ol, 5,6,7,8-tetramethylnaphthalene-1-ol, naphthalene-1,5-diol, naphthalene-1,6-diol, naphthalene-1,7-diol, 2-methoxynaphthalene-1-ol, 3-methoxynaphthalene-1-ol, 5-methoxynaphthalene-1-ol, 6-methoxynaphthalene-1-ol and 7-methoxynaphthalene-1-ol, in particular 1-naphthol or 2-methylnaphthalene-1-ol.

[0027] R 1 and R 2 and R 3 and R 4 are, independently of each other, H or C 1~4 alkyl, preferably H or CH3, provided that the substituent R 1 and R 2 and R 3 and R 4 The condition is that at least one of the above does not represent H. R 5 =R6 =R 7 It is more preferred that =H. R 2 =H, and R 1 More preferably =H or CH3. It is particularly preferred that the compound of formula (II) is:

[0028] In photo-oxidation, the reaction of formula (III) [ka] (In the formula, R 8 ,R 8’ ,R 8’’ and R 8’’’ are, independently of each other, H or C 1~4 represents an alkyl group, Or, R 8 and R 8’ and / or R 8’’ and R 8’’’ forms a 5- or 6-membered ring together with N, X - represents an anion, however, residue R 8 ,R 8’ ,R 8’’ and R 8’’’ provided that at least one of is different from H) is used.

[0029] In one embodiment, R 8 and R 8’ and / or R 8’’ and R 8’’’ are both -(CH2)5- or -(CH2)2-NH-(CH2)2- or -(CH2)2-N(C 1~4 alkyl)-(CH2)2- or -(CH2)2-S-(CH2)2- or -(CH2)2-O-(CH2)2-.

[0030] R 8 =R 8’’ and / or R 8’ =R 8’’’It is more preferable that R 8 =R 8’ =R 8’’ =R 8’’’ It is more preferable that:

[0031] More preferably, the substituent R 8 ,R 8’ ,R 8’’ and R 8’’’ is C 1~4 represents an alkyl group, and even more preferably, R 8 =R 8’ =R 8’’ =R 8’’’ = methyl or ethyl.

[0032] Most preferably, R 8 =R 8’ =R 8’’ =R 8’’’ =CH3.

[0033] In general formula (III), X - represents an anion. The role of the anion is to balance the charge of the cation, represented by the part in brackets ([)(]) in the above formula. Therefore, in principle, any anion can be used.

[0034] Preferably, X - represents a halide, most preferably chloride.

[0035] Preferably, the compound of formula (III) is methylene blue. More preferred is the compound of formula (III) in the form of a double salt with zinc chloride, in particular a double salt of methylene blue and zinc chloride, or in the form of a hydrate, preferably methylene blue hydrate (CAS: 122965-43-9).

[0036] Photosensitizers of formula (III) have been found to be particularly suitable for the photooxidation of compounds of formula (II).

[0037] The photooxidation mentioned above has a peak wavelength (λ) in its spectrum in the range of 580-780 nm. maxIt is essential to use light having a

[0038] In one preferred embodiment, the spectrum has a peak wavelength (λ ) in the range of 625 to 740 nm. max ) is used, which corresponds to light perceived as red.

[0039] In another more preferred embodiment, the spectrum has a peak wavelength (λ ) in the range of 585 nm to 625 nm. max ) is used, which corresponds to light perceived as orange.

[0040] This light is primarily in the high wavelength range of the visible spectrum.

[0041] In a further preferred embodiment, the light used is characterized in that more than 80% of the light has a wavelength between 525 and 780 nm, preferably more than 80% of the light has a wavelength between 525 and 700 nm, and more preferably more than 65% of the emitted light has a wavelength between 550 and 650 nm.

[0042] It is therefore important that the light used has a spectrum that contains very little light with wavelengths less than 580 nm, and it is essential that green, blue, and violet colored light, or light with significant amounts of green, blue, and violet colored light in its spectrum, is known to be unsuitable for the photooxidation described above.

[0043] In one embodiment, the light used for photo-oxidation can be achieved by filtering undesired light wavelengths from the light source, for example, a light source with polychromatic or white light emission can be filtered with a filter that blocks undesired wavelengths.

[0044] There are a variety of known and commercially available possibilities for such filters that use different physical processes to filter light, such as absorption, dichroic, monochromatic, bandpass, shortpass, or wedge filters.

[0045] Absorption or cut-off filters are particularly useful.

[0046] FIG. 1a shows a schematic diagram of this embodiment. A light source (1) emits radiation of various wavelengths, including desired wavelengths (2a) and undesired wavelengths (2b). The light source is preferably white light, more preferably a white LED. A filter (6) is placed between the light source (1) and a photoreactor having transparent walls (4). The filter (6) filters out the undesired wavelengths of light, leaving a peak wavelength (λ) in its spectrum in the range of 580-780 nm. max The filter (6) is preferably an "orange filter" or a "red filter", i.e., a filter that passes only light having a wavelength of 585 to 625 nm or 625 to 740 nm. At least oxygen and the compound of formula (II), water and at least one C 1~8 Alkanol or at least one C 2~4 The reaction mixture (3), which comprises a solvent mixture of alkylene diol, is inside the photoreactor (5).

[0047] By photoreaction, the compound of formula (I) is produced by photochemical reaction from the compound of formula (II) and oxygen, in particular in a gas mixture containing at least 20% by volume of oxygen.

[0048] A particularly preferred example of this embodiment is a white LED, whose light is filtered so that all light other than the desired wavelengths is blocked, or at least largely absorbed (e.g., using an "orange filter" (which transmits only light between 585 and 625 nm) or a "red filter" (which transmits only light between 625 and 740 nm)).

[0049] Therefore, the source of light is preferably a white LED lamp in combination with a filter that blocks wavelengths below 500 nm, in particular below 625 nm.

[0050] In a further embodiment, the light used for photo-oxidation can be generated by a respective light source that emits light of the desired wavelength.

[0051] Figure 1b shows a schematic diagram of this embodiment. The light source (1) emits radiation of the desired wavelength (2a) with a peak wavelength (λ) in its spectrum in the range of 580-780 nm. max The light source is preferably orange or red light, more preferably an orange or red LED, with a peak wavelength (λ ) in its spectrum in the range of 580 to 780 nm. max ) to provide light.

[0052] at least oxygen and a compound of formula (II), water and at least one C 1~8 Alkanol or at least one C 2~4 The reaction mixture (3) containing the alkylene diol and the solvent mixture is inside the photoreactor (5). The compound of formula (I) is produced by photochemical reaction of the compound of formula (II) with oxygen.

[0053] A specific example of the light source in this embodiment is a red LED or a red or orange laser, preferably a red or orange LED lamp. Red and orange LED lamps are widely available commercially. Red and orange LEDs can provide high-intensity red or orange light. In a preferred embodiment, a flexible strip having multiple individual LEDs is incorporated into the strip. This allows for ensuring radial orientation of the LEDs around a curved surface, such as a transparent tube, by simply wrapping the strip around the tube, preferably in a spiral fashion.

[0054] Photooxidation occurs when water and at least one C 1~8 Alkanol or at least one C 2~4 It is carried out in a solvent mixture with an alkylene diol.

[0055] C 1~8The alkanol is preferably selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol, heptanol and hexanol, more preferably selected from the group consisting of methanol, ethanol and isopropanol.

[0056] C 2~4 The alkylene diol is preferably selected from the group consisting of ethane-1,2-diol, propane-1,2-diol, propane-1,3-diol, butane-1,3-diol, butane-1,4-diol, butane-1,2-diol and butane-2,3-diol, and more preferably selected from the group consisting of ethane-1,2-diol, propane-1,2-diol and propane-1,3-diol.

[0057] The solvent mixture consists of water and at least one C 1~8 Alkanol or at least one C 2~4 It is preferably a mixture with an alkylene diol to form a homogeneous phase.

[0058] The solvent mixture consists of water and at least one C 1~8 Alkanol or at least one C 2~4 A more preferred solvent mixture is a mixture of water and C alkylene diol. 1~8 It is a mixture with alkanols.

[0059] More preferably, the solvent mixture is a mixture of water with methanol and / or ethanol and / or isopropanol.

[0060] C 1~8 Alkanols and C 2~4 The volume ratio of water to the total alkylene diol is preferably in the range of 1:10 to 1:1, particularly preferably 1:5 to 1:2.

[0061] In a highly preferred embodiment, the solvent mixture is a mixture of water and methanol, preferably in a volume ratio of water to methanol in the range of 1:20 to 1:2, preferably 1:10 to 1:2, more preferably 1:6 to 1:3, and most preferably 1:4.

[0062] Photo-oxidation occurs when water and at least one C 1~8 Alkanol or at least one C 2~4 An important advantage of the present invention is that it is carried out in a solvent mixture consisting of alkylenediols, which are very favourable solvents from an ecological and ecotoxicological point of view, as well as being economically advantageous. It is therefore highly preferred to carry out the process in the absence of chlorinated solvents.

[0063] The concentration of the compound of formula (II) is preferably in the range of 0.002 to 2.0 mol / l, more preferably 0.01 to 0.2 mol / l at the start of photooxidation.

[0064] More preferably, the ratio of the compound of formula (III) to the compound of formula (II) is in the range of 0.005 to 20 mol %, preferably 0.05 to 20 mol %, and more preferably 0.2 to 10 mol %.

[0065] In one embodiment, oxygen is used in the form of a mixture comprising oxygen and an inert gas. The amount of oxygen in such a mixture comprising oxygen and an inert gas is preferably at least 15% by volume, in particular at least 20% by volume. Such a mixture may be, for example, a binary mixture, such as an oxygen / nitrogen mixture or an oxygen / argon mixture. The aforementioned mixture may consist of or contain two or more inert gases. It is particularly preferred to use air as such a mixture comprising oxygen and an inert gas.

[0066] In a preferred embodiment, oxygen is used in substantially pure form, ie the amount of oxygen in the gas is between 90% and 100%, more preferably between 95% and 100%, even more preferably between 99% and 100%.

[0067] The photo-oxidation can be carried out at atmospheric pressure or under increased pressure, preferably under increased pressure, in particular above 2 bar, preferably above 3 bar, more preferably between 2 and 20 bar.

[0068] The photooxidation is carried out in a suitable photoreactor. Preferred photoreactors are flow reactors, especially spiral flow reactors.

[0069] The individual components can be introduced into the photoreactor separately or as a mixture. Preferably, the reaction mixture is prepared prior to entering the photoreactor.

[0070] In one preferred embodiment, the oxygen-containing solvent mixture is mixed with the compound of formula (II) before it enters the photoreactor.

[0071] In another preferred embodiment, the solvent mixture is already mixed with the oxygen-containing compound of formula (II) before entering the photoreactor.

[0072] In a most preferred embodiment, oxygen is added to a premix comprising at least the compound of formula (II) and the solvent mixture.

[0073] The reaction is preferably conducted in such a way that the pressure of the oxygen is controlled by appropriate valves and mass flow controllers. Such process control equipment and methods for photoreactions using liquids and gases are known to those skilled in the art. [Brief explanation of the drawings]

[0074] [Figure 1a] Figure 1 shows a schematic diagram of photooxidation using a light source and filters to generate light with a peak wavelength (λ) in its spectrum in the range of 580-780 nm. [Figure 1b] A schematic diagram of photo-oxidation is shown using a light source with a peak wavelength (λmax) in its spectrum ranging from 580 to 780 nm. [Figure 2a] A schematic diagram of one of the experimental layouts is shown. [Figure 2b] Schematics of different experimental layouts are shown. [Figure 2c] 1 shows a schematic diagram of another different experimental layout. [Figure 3] 1 shows the normalized emission spectra of the light used for photooxidation in the experiment using an orange filter and of white light.

[0075] In Figure 2a, one preferred experimental layout is shown: a mixture of at least a compound of formula (II) and a photosensitizer of formula (III), water and at least one C 1~8 Alkanol or at least one C 2~4 A vessel containing a premix (10) comprising a solvent mixture with alkylene diol is pumped into the photoreactor (5) by a pump (7). Before entering the photoreactor (5), oxygen (11) is mixed with the premix to form the photooxidation reaction mixture (3). The amount of oxygen mixed is controlled by a mass flow controller (8). Around the transparent wall (4) of the linear tubular photoreactor (5), light sources (1) are arranged, in particular in a spiral arrangement of LEDs. The light sources (1) are preferably white LEDs. A filter (6) is arranged between the transparent wall (4) and the light source (1), which filters light with a peak wavelength (λ) in its spectrum in the range of 580-780 nm. max The filter (6) can provide light (2a) having a peak wavelength (λ ) in its spectrum, in particular in the range of 585 to 625 nm or 625 to 740 nm, respectively. max ) resulting in light with a flow rate of 1000 s. The photoreactor (5) is preferably a spiral flow reactor. At the exit of the photoreactor, a back pressure regulator (9) is placed before the product is collected in a collection vessel (12). This experimental layout, especially the light source and photoreactor combination, is preferably used for larger volume photoreactions.

[0076] In Figure 2b, another preferred experimental layout is shown. A mixture of at least a compound of formula (II) and a photosensitizer of formula (III), water and at least one C 1~8Alkanol or at least one C 2~4 A vessel containing a premix (10) comprising an alkylene diol and a solvent mixture is pumped into the photoreactor (5) by a pump (7). Before entering the photoreactor (5), oxygen (11) is mixed with the premix to form the photooxidation reaction mixture (3). The amount of oxygen mixed is controlled by a mass flow controller (8). A filter (6) is placed between the transparent wall (4) of the photoreactor (5) and the light source (1), preferably a white LED, to filter out a peak wavelength (λ) in its spectrum in the range of 580-780 nm. max ) can provide light (2a) having a wavelength of 1000 nm. In this representation, only one light source (1) and one filter (6) are shown. Of course, it is possible that several such light sources (1) combined with filters (6) are arranged around the photoreactor (5) in the form of a spiral flow reactor, so as to even allow illumination of the entire photoreactor (5). The filters (6) are in particular orange or red filters, respectively, having peak wavelengths (λ) in their spectrum, in particular in the range of 585-625 nm or 625-740 nm, respectively. max ) resulting in light with a wavelength of 1000 keV. Light with undesired wavelengths (2b) is filtered by a filter (6). At the exit of the photoreactor, a backpressure regulator (9) is placed before the product is finally collected in a collection vessel (12). This experimental layout, and in particular the light source and photoreactor combination, is preferably used for smaller volume photoreactions.

[0077] In Figure 2c, another preferred experimental layout is depicted. At least a compound of formula (II) and a photosensitizer of formula (III), water and at least one C 1~8 Alkanol or at least one C 2~4 A vessel containing a premix (10) comprising an alkylene diol and a solvent mixture is pumped into the photoreactor (5) by a pump (7). Before entering the photoreactor (5), oxygen (11) is mixed with the premix to form the photooxidation reaction mixture (3). The amount of oxygen mixed is controlled by a mass flow controller (8).

[0078] In this embodiment, a light source (1), preferably a white LED, is arranged in the hollow space formed by the spiral windings of a spiral-shaped flow reactor (5). A filter (6) is placed around the light source (1), i.e., between the transparent wall (4) of the photoreactor (5) and the light source (1), to filter a peak wavelength (λ) in its spectrum in the range of 580-780 nm. max The filter (6) can provide light (2a) having a peak wavelength (λ ) in its spectrum, in particular in the range of 585 to 625 nm or 625 to 740 nm, respectively. max ) resulting in light having a wavelength of 1000 Å. Light having undesired wavelengths (2b) is filtered by a filter (6). At the exit of the photoreactor, a back pressure regulator (9) is placed before the product is finally collected in a collection vessel (12).

[0079] This experimental layout, especially the light source and photoreactor combination, is preferably used for smaller volume photoreactions.

[0080] In yet another embodiment, the light source (1) and filter (6) of Figures 2b) and 2c) are combined, in other words the filter and light source can be arranged on the outside of the photoreactor wall arranged inside and outside the space formed by the helical turns of the spiral flow photoreactor (5). [Explanation of symbols]

[0081] 1 light source 2a Light of desired wavelength 2b Undesirable wavelengths of light 3. Photooxidation reaction mixture 4. Transparent walls of the photoreactor 5. Photoreactor 6 Filters 7. Pump 8 Mass Flow Controller 9 Back pressure regulator 10 Premix 11 Oxygen 12 Collection container

[0082] [Example] The present invention is further illustrated by the following experiments.

[0083] [Experimental layout] In the following experiments, the experimental layout represented schematically in Figure 2c is used.

[0084] The solvent premix (10), the solvent mixture, and the containers containing the material to be photooxidized and the photosensitizer are pumped by a pump (7) into the photoreactor (5), a spiral flow reactor (4.6 mL coil reactor). Before entering the photoreactor (5), oxygen (11) is mixed into the premix to form the photooxidation reaction mixture (3). The amount of oxygen mixed is controlled by a mass flow controller (8). The light source (1), a white LED (4000 lm, 32 W, 4100 K) (LSo, emission spectrum, see Figure 3), is filtered by an orange filter (6) to screen out undesired wavelengths (2b), allowing only the desired wavelengths (2a) to strike the transparent wall (4) of the photoreactor (5). The photoreactor (5) is fan-cooled and has an inner glass cylinder wrapped around the LED lamp (1) with the respective filters (6) between the LED lamp and the wall of the photoreactor (5). At the exit of the photoreactor, a back pressure regulator (9) is placed before the product is finally collected in a collection vessel (12). The oxygen pressure and flow rate, as well as the residence time (t R ) are indicated for each experiment.

[0085] The amount of product formed was determined by GC-FID and 1 Determined by 1 H-NMR using durene as an internal standard.

[0086] The light used in the photooxidation experiment is -White LED light (LSw) -White LED light with an orange filter (LSo).

[0087] In Figure 3, the spectrum of the light used in the photooxidation experiments between wavelengths of 325 and 700 nm is shown as the normalized relative intensity (I) of light incident on the transparent wall of the photoreactor. e,norm ) are used.

[0088] [Experiment Series 1] In the first series, various substrates were photooxidized (0.02 mol / L) in a 4 / 1 (vol / vol) methanol / water solvent mixture using methylene blue (0.9 mol%) in air (10 bar, 1.35 mL / min) at 35 °C (flow rate 0.25 mL / min, t R = 23 min). The results are summarized in Table 1.

[0089] [Table 1]

[0090] [Experiment Series 2] In the second series, various substrates were photooxidized (0.02 mol / L) in a 4 / 1 (vol / vol) methanol / water solvent mixture using methylene blue (0.9 mol%) in air (10 bar, 0.25–1.35 mL / min) at 35 °C. The residence time was chosen to achieve a conversion rate of over 99%.

[0091] The results are summarized in Table 2.

[0092] [Table 2]

[0093] [Experiment Series 3] In the third series, various substrates were photooxidized (0.02 mol / L) in a 4 / 1 (vol / vol) methanol / water solvent mixture using methylene blue (0.9 mol%) in air (10 bar, 0.5–1.5 mL / min) at 35 °C. The residence time was chosen to achieve >99% conversion.

[0094] The results are summarized in Table 3.

[0095] [Table 3]

[0096] Tables 1-3 show that compounds of formula (II) exhibit significantly higher yields of producing their respective quinones (products) in photooxidation compared to other phenols with similar structures as starting materials (substrates).

Claims

1. A process for preparing a compound of formula (I) from a compound of formula (II) by photooxidation, comprising: 【Chemical 1】 (In the formula, R １ and R ２ are each independently H or C １～４ Alkyl group or halogenated C １～４ Alkyl group, OR ９ group or —CH ２ -OR ９ represents a group, R ３ and R ４ are each independently H or C １～４ Alkyl group or halogenated C １～４ Alkyl group or OR ９ group or —CH ２ -OR ９ group, or both of the formula 【Chemistry 2】 forming a group of In the formula, R ５ and R ６ and R ７ are each independently H or OH or C １～４ Alkyl group or OR ９ represents a group, However, residue R ５ and R ６ and R ７ and at least two of the following are different from OH: The dotted line represents the bond through which the substituent of said formula is attached to the remainder of the compound of formula (I) or formula (II); R ９ is C １～４ alkyl group), Water and at least one C １～８ alkanol or at least one C ２～４ In a solvent mixture of an alkylene diol and oxygen, 【Chemistry 3】 (In the formula, R ８ , R ８’ , R ８’’ and R ８’’’ are, independently of one another, H or C １～４ represents an alkyl group, Or, R ８ and R ８’ and / or R ８’’ and R ８’’’ forms a 5- or 6-membered ring together with N, X － represents an anion, however, R １ =R ２ =R ３ =CH ３ If R ４ is different from H, R １ =R ２ =R ４ =CH ３ If R ３ is different from H, residue R １ , R ２ , R ３ and R ４ At least one of is different from H, residue R ８ , R ８’ , R ８’’ and R ８’’’ and The spectrum has a peak wavelength (λ ｍａｘ 2. A process for producing a compound of formula (I) from a compound of formula (II) using light having a formula:

2. The light used had a peak wavelength (λ ) in its spectrum ranging from 585 nm to 625 nm. ｍａｘ 2. The process of claim 1, wherein

3. The light used had a peak wavelength (λ ) in its spectrum ranging from 625 nm to 740 nm. ｍａｘ 2. The process of claim 1, wherein

4. A process according to any one of claims 1 to 3, characterized in that more than 80% of the light has a wavelength between 525 and 780 nm.

5. 5. The process according to claim 1, wherein the solvent mixture is a mixture of water with methanol and / or ethanol and / or isopropanol.

6. C １～８ Alkanol and C ２～４ 6. The process according to any one of claims 1 to 5, characterized in that the volume ratio of water to the total alkylene diols is in the range of 1:10 to 1:

1.

7. The process according to any one of claims 1 to 6, characterized in that the light source is a red or orange LED lamp.

8. 8. The process according to any one of claims 1 to 7, characterized in that the light source is a white LED lamp combined with a filter that blocks wavelengths below 500 nm.

9. R ８ =R ８’ =R ８’’ =R ８’’’ =CH ３ The process according to any one of claims 1 to 8, characterized in that:

10. R １ and R ２ and R ３ and R ４ are each independently H or C １～４ represents alkyl, provided that the substituent R １ and R ２ and R ３ and R ４ The process according to any one of claims 1 to 9, characterized in that at least one of does not represent H.

11. R ５ =R ６ =R ７ 10. The process according to claim 1, wherein: =H.

12. R ２ = H and R １ = H or CH ３ 11. The process according to claim 10, wherein

13. X － The process according to any one of claims 1 to 12, characterized in that represents a halide.

14. 14. The process according to any one of claims 1 to 13, characterized in that the concentration of the compound of formula (II) ranges from 0.002 to 2.0 mol / l at the start of the photo-oxidation.

15. 15. The process according to any one of claims 1 to 14, characterized in that the ratio of compounds of formula (III) to compounds of formula (II) ranges from 0.005 to 20 mol%.

16. The process according to any one of claims 1 to 15, characterized in that the photooxidation is carried out in a flow reactor.

Images