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EP-4739648-A1 - PHOTOISOMERIZATION OF GERANIAL AND NERAL

EP4739648A1EP 4739648 A1EP4739648 A1EP 4739648A1EP-4739648-A1

Abstract

The present invention relates to a method, comprising the isomerization of neral of formula (II) to geranial of formula (I), or the isomerization of geranial to neral, characterized in that (a) the isomerization is accomplished by irradiation with light. The method according to the present invention makes it possible to convert an undesired isomer, which is an unavoidable by-product generated during the production of neral and/or geranial, into a desired isomer highly efficiently, thus greatly improving the economic performance of the method for producing the desired isomer (in high yield by avoiding cost intensive distillation and with avoiding possible side products).

Inventors

  • SCHAEFER, BERND
  • SCHELWIES, Mathias

Assignees

  • BASF SE

Dates

Publication Date
20260513
Application Date
20240627

Claims (20)

  1. 1. A method, comprising the isomerization of neral of formula geranial of formula r the isomerization of geranial to neral, characterized in that (a) the isomerization is accomplished by irradiation with light.
  2. 2. The method according to claim 1, which is a method for the preparation of enriched or pure neral, comprising the steps a) the isomerization of the enriched or pure geranial to a mixture of neral and geranial by irradiation with light; b) the separation, especially the distillative separation of the mixture comprising geranial and neral obtained in step a) to give the product, 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. 3. The method according to claim 2, additionally comprising as step 0) the provision of enriched or pure geranial by distillative separation of mixtures comprising geranial and neral.
  4. 4. The method according to claim 1 , which is a method for the preparation of enriched or pure geranial, comprising the steps a) the isomerization of the enriched or pure neral to a mixture of neral and geranial by irradiation with light; b) the separation, especially the distillative separation of the mixture comprising geranial and neral obtained in step a) to give the product, enriched or pure geranial, and enriched or pure neral; and c) optionally recycling of the enriched or pure neral obtained in step b) to step a).
  5. 5. The method according to claim 4, additionally comprising as step 0) the provision of enriched or pure neral by distillative separation of mixtures comprising geranial and neral.
  6. 6. The method according to any of claims 1 to 3, wherein in step a) a solution of the geranial in a solvent is irradiated with light, or the method according to any of claims 1 , 4, or 5, wherein in step a) a solution of the neral in a solvent is irradiated with light, wherein the solvent is preferably selected from water, dichloromethane, trichloromethane, tetrachloromethane, CS2, Ci-C4alcohols, chlorobenzene, fluorobenzene, trifluoromethylbenzene, acetonitrile, dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), ethylacetate, acetone and mixtures thereof.
  7. 7. The method according to any of claims 1 to 3, or 6, wherein in step a) the geranial is irradiated with light, in particular monochromatic light, in the presence of a sensitizer, or the method according to any of claims 1 , 4, 5, or 6, wherein in step a) the neral is irradiated with light, in particular monochromatic light, in the presence of a sensitizer.
  8. 8. The method according to claim 7, wherein the sensitizer is selected from [lr(dF(CF 3 )ppy) 2 (bpy)]PF 6 , (lr[dF(CF 3 )ppy]2(dtbbpy))PF 6 , (lr[dF(CF 3 )ppy] 2 (dtbpy))PF 6 , (lr[dF(Me)ppy] 2 (dtbbpy))PF 6 , [lr(dtbbpy)(ppy) 2 ]PF 6 , lr(ppy) 3 , Ru(bpy) 3 CI 3 , [Ru(bpy) 3 ](PFe)2, benzophenone, thioxanthen-9-one, Michler's Ketone, tetramethoxy- antracen-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-tetrakis(carbazol-9-yl)-4,6- dicyanobenzene (4CzlPN), 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-Mesityl-10- methylacridinium tetrafluoroborate, mesityl-10-methylacridinium perchlorate, Eosin Y, Eosin B, 9,10-diphenylanthracene, 9,10-dicyanoanthracene, Rose Bengal and mixtures thereof.
  9. 9. The method according to any of claims 1 to 8, wherein in step a) the geranial is irradiated with light, in particular monochromatic light, in the wavelength range of 350 to 490 nm; or in step a) the neral is irradiated with light, in particular monochromatic light, in the wavelength range of 350 to 490 nm, 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 350 nm to 490 nm and its monomodal emission spectrum preferably exhibiting a halfwidth of not more than +/- 100 nm, preferably not more than +/- 60 nm, such as +/- 10 to +/- 30 nm, in relation to the wavelength of the emission maximum, and /or wherein preferably the geranial and/or neral is irradiated in the presence of a sensitizer in accordance with any of claims 7 or 8.
  10. 10. The method according to any of claims 1 to 3, wherein in step a) the geranial in neat form is irradiated with light, in particular monochromatic light, or the method according to any of claims 1 , 4 and 5, wherein in step a) the neral in neat form is irradiated with light, in particular monochromatic light, or the method according to any of claims 1 to 5, wherein in step a) a mixture comprising or consisting of geranial and neral in neat form is irradiated with light, in particular monochromatic light.
  11. 11. The method according to any of claims 1-8 or 10, wherein in step a) the geranial is irradiated with light, in particular monochromatic light, in the wavelength range of 300 to 420 nm; or in step a) the neral is irradiated with light, in particular monochromatic light, in the wavelength range of 300 to 420 nm; in step a) a mixture comprising or consisting of geranial and neral in neat form is irradiated with light, in particular monochromatic light, 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 preferably exhibiting a halfwidth of not more than +/- 100 nm, preferably not more than +/- 60 nm, such as +/- 10 to +/- 30 nm, in relation to the wavelength of the emission maximum, and/or wherein preferably the geranial in neat form, the neral in neat form or a mixture comprising or consisting of neral and geranial in neat form is irradiated with light, in particular monochromatic light, in accordance with claims 10.
  12. 12. The method according to any of claims 1 to 11 , wherein step a) is done in a temperature range of -20 to 100 ° C.
  13. 13. The method according to any of claims 1 to 12, wherein step a) is done in a pressure range from 1 mbar to 20 bar.
  14. 14. The method according to any of claims 1 to 13, wherein step a) is carried out in a continuously stirred reaction vessel, in a pumping circuit, or in a continuous flow reactor.
  15. 15. The method according to any of claims 1 to 14, wherein the irradiation with light is accomplished by use of at least one LED (light emitting diode), or laser.
  16. 16. The method according to any of claims 1-3 or 6-15, wherein in step a) the geranial is irradiated with monochromatic light.
  17. 17. The method according to any of claims 1 or 4-15, wherein in step a) the neral is irradiated with monochromatic light.
  18. 18. The method according to any of claims 1 to 17, wherein the method is a method for producing a desired isomer, in particular neral or geranial, optionally comprised in a mixture comprising neral and geranial.
  19. 19. The method according to any of claims 1 to 18, wherein the method is a method for isomerization geranial to neral or for isomerization of neral to geranial.
  20. 20. The method according to any of claims 1 to 19, wherein the method is a method for the preparation of enriched or pure neral.

Description

Photoisomerization of Geranial and Neral Description The present invention relates to a method, comprising the isomerization of neral of formula r the isomerization of geranial to neral, characterized in that (a) the isomerization is accomplished by irradiation with light. The method according to the present invention makes it possible to convert an undesired isomer, which is an unavoidable by-product generated during the production of neral and/or geranial, into a desired isomer highly efficiently, thus greatly improving the economic performance of the method for producing the desired isomer (in high yield by expending as few energy as possible and with avoiding possible side products). Prior Art CN112142583A relates to a method for preparing neral of formula from geranial of formula characterized in that the geranial is isomerized into neral in the presence of carbon monoxide and a catalyst obtained by reacting triethylaluminum with bis-diarylphenol ligand of formula which R1, R2, R3 and R4 are independently of one another selected from Ce-Cisaryl, R5 is selected from hydrogen, Ci-Cealkyl and Ci-Ceperfluoroalkyl. CN107879914A relates to a method for preparing neral by efficiently rectifying citral which comprises the following steps: the citral containing two isomers neral and geranial is rectified and separated by a rectifying tower, and a neral product is obtained at the tower top of the rectifying tower, wherein iodine and phosphorus catalytic active centers are loaded on a stripping section filler of the rectifying tower, so that a material which flows through the tower bottom and is rich in geranial is catalytically converted into a material with an increased neral proportion. CN112125782A relates to a method for preparing high-purity nerol and geranial by hydrogenating citral which is characterized by comprising the steps of selectively carrying out catalytic hydrogenation reaction on nerol in citral to obtain nerol by adopting a novel transition metal composite catalyst, carrying out no catalytic reaction on geranial, and carrying out rectification separation on reaction products to obtain the high-purity nerol and geranial; wherein, the novel transition metal composite catalyst comprises a transition metal compound and a chiral spiro bisoxazoline ligand with a spiro indane skeleton. RU2579122 relates to a method of obtaining the geranial from the mixture of isomers of geranial and neral (citral), based on conducting of the transformations of citral in the presence of acid catalysts, preferably montmorillonite clay, wherein the isolation of geranial from the reaction mixture can be achieved by column chromatography or distillation at reduced pressure. Wout A. M. Wolken et al., J. Agric. Food Chem., 48 (2000) 5401 -5405 reports that under alkaline conditions, amino acids or proteins catalyze the deacetylation of citral, a major aroma component, resulting in methylheptenone and acetaldehyde formation. 3- Hydroxycitronellal is an intermediate in this reaction. Amino acids also catalyze the cis-trans isomerization of the pure isomers of citral, geranial, and neral. The glycine-catalyzed isomerization of geranial is a relatively fast process (Figure 1A). After 80 min, an equilibrium was reached with 60% of geranial and 40% neral. Starting with neral, the same equilibrium was reached (Figure 1 B). O.S. Bokareva, Computational and Theoretical Chemistry 1149 (2019) 8-16 relates to a quantum-chemical study of structures and conformational dynamics of trans- and ciscrotonaldehydes in excited electronic states. Jens Holz et al., Adv. Synth. Catal. 2017, 359, 4379 - 4387 describes the highly chemoselective hydrogenation of neral affording citronellal. The reaction has been conducted with homogeneous rhodium complexes. A high activity and chemoselectivity in favor of the desired citronellal is achieved at 0.1 MPa and room temperature. Under the same conditions, geranial is also reduced to citronellal. CN116474824A relates to a catalyst for isomerising neral to geranial, characterized in that: the catalyst is one or more of citric acid, tartaric acid, amino acid and malic acid and a method for increasing the geranial content in citral, which comprises adding the catalyst to citral. R. C. Cookson et al., Tetrahedron 19 (1963) pages 1995-2007 concerns the cyclization of citral to 2-isopropenyl-5-methylcyclopentane-carboxaldehyde by UV irradiation using a medium-pressure mercury arc lamp. It is stated on page 1 , footnote * that the sample used was a 1 :1 mixture of cis and trans isomers and the interconversion between the geometrical isomers (of citral) is probably faster than cyclisation. W. L. Dilling, Chemical Reviews (1966) pages 373-393 relates to the intramolecular photochemical cycloaddition reactions of nonconjugated olefins. Cis- and trans citral on irradiation in either cyclohexane or ethanol results in the cycloaddition product XVIII and a hydrogen migration product XIX (page 376, column