DE963958C - Process for the preparation of 4,4'-disubstituted ª ‰ -carotene - Google Patents

Description

Process for the preparation of 4,4'-disubstituted p-carotenes the The invention relates to a process for the production of new carotenoids. This The method is that acetylene in a known manner by a organometallic reaction on both sides with 8- [2 ', 6', 6'-trimethylcyclohexen- (2 ') - ylidene- (1')] - 2, 6-dimethyloctatriene- (2, 4, 6) -al- (I) - hereinafter referred to as dehydro-retro-Cl-9-aldehyde - condensed, the formed I, I8-di- [2 ', 6', 6'-trimethylcyclohexen- (2 ') - ylidene- (I') I-3, 7, I2, I6-tetramethyl-8, II-dioxyoctadecahexaen- (2, 4, 6, I2, I4, 16) -in- (9) - in the following bisdehydro-retro-C ,, - called diol - halogenation with allyl rearrangement treated, in the resulting I5, I5'-DehydrO-4, 4'-dihalo-ß-carotene the halogen atoms in the usual way by oxy resp.

Replaced acyloxy groups, the obtained 15, 15'-dehydro-4, 4'-dioxyß-carotene which is optionally esterified in the 4, 4'-position at the triple bond is catalytically partially hydrogenated in a known manner and the hydrogenation product formed isomerized in a known manner, whereby before the hydrogenation or before the isomerization, the acyloxy groups can be saponified to give oxy groups and / or the oxy groups can be oxidized to give oxo groups. The reactions according to the invention are compiled in the reaction scheme below: OHO Dehydro-retro-019-aldeliyd / / / OHO OH HOÄ condensation OH 0 Bisdehydro-retro-C40 diol g t OH Halogenation with allyl rearrangement Hal 15, 15'-dehydro- 4,4'-dihalo-fl-carotene Hal Replacement of halogen with hydroxyl Replacement of halogen by hydroxyl v 0 # jxx) y 15, 4'-dioxy, 4,4 -dloxy-β-carotene OH Partial hydrogenation Isomerization OH 4,4 '-Dioxy-fl- c arotin) {$ ¼ \ M¼Mü \\\\\ Yi OH The dehydroretro-Cl9-aldehyde used as the starting material can be prepared, for example, as follows: ß-ionone is condensed by means of a glycidate reaction with ethyl chloroacetate, the resulting glycidate is saponified under alkaline conditions, the 4- [2 ', 6', 6'-trimethylcyclohexene ( I ') - yl- (I')] - 2-methylbutene- (2) -al- (1) brominated by means of N-bromosuccinimide, split off from the bromination product with quinoline hydrogen bromide, the 4- [2 ', 6', 6'-Trimethylcyclohexen- (2 ') - yliden- (I')] - 2-methylbutene- (2) -al- (I) acetalized, the acetal formed is condensed with a vinyl ether in the presence of an acidic condensing agent such as zinc chloride, the condensation product obtained is boiled with acetic acid and sodium acetate, with 6- [2 ', 6', 6'-trimethylcyclohexen- (2 ') -yliden- (1')] -4-methylhexadiene- (2, 4) -al- ( 1) arises.

This is in turn acetalized, the acetal formed in the presence an acidic condensing agent such as zinc chloride, condensed with a propenyl ether and the condensation product obtained is boiled with acetic acid and sodium acetate.

The first stage of the process of the invention is acetylene in a manner known per se by organometallic reaction on both sides with the dehydro-retro-Cl9-aldehyde condensed. For this you can use an acetylenedimagnesium halide with the double molar Condense the amount of dehydro-retro-C1 9-aldehyde according to Grignard. Acetylenedimagnesium halides can in a manner known per se by the action of acetylene on a solution of alkyl magnesium halides in an inert solvent. Preferably an ethereal solution of the alkyl magnesium halide in an acetylene atmosphere is used stirred or shaken for several hours. As alkyl magnesium halides are suitable for example ethyl, butyl and hexyl magnesium bromides or chlorides. The acetylenedimagnesium halides In this reaction separate out as heavy oils or in solid form. Appropriate then 2 moles of dehydro-retro-C ,, - aldehyde in an inert solvent, preferably Ether, dissolved, added to the well-stirred suspension of the acetylenedimagnesium halide, and the mixture is then allowed to stand for several hours at room temperature or at the boiling temperature of the solvent stirred. Obtained after hydrolysis of the condensation product the bisdehydro-retro-C40-diol as a very viscous oil, which in the ultraviolet spectrum has an absorption maximum at 349.5 m, u (in petroleum ether). The Zerewitinoff determination indicates 2 active hydrogen atoms. Another embodiment of the first stage of the process according to the invention consists in that I mol of the dehydro-retro-C ,, - aldehyde can react in liquid ammonia with an alkali or alkaline earth acetylide and the condensation product formed, expediently after hydrolysis to I0- [2 ', 6', 6 '-Trimethylcyclohexen- (2') - yliden- (I ')] - 4, 8-dimethyidecatriene- (4, 6, 8) -in- (I) -ol- (3) - hereinafter referred to as dehydro-retro-C2l-acetylenecarbinol - by means of an organometallic Reaction with a second mole of dehydro-retro-Cl9-aldehyde. The condensation in liquid ammonia you can under increased pressure at room temperature or below Perform normal pressure at the boiling point of ammonia. Preferably used lithium acetylide is used for condensation. The dehydro-retro-O1 9-aldehyde can be used in one inert solvents, for example in ether, are added. The condensation product is best done by adding an ammonium salt before removing the ammonia or hydrolyzed by adding acid after removing the ammonia. The dehydro-retro-C2l-acetylenecarbinol shows in the ultraviolet spectrum an absorption maximum at 349 mµ (in petroleum ether) and represents a thick oil. The Zerewitinoff determination shows in the cold I and 2 active hydrogen atoms in heat. The condensation of the dehydro-retro-C21-acetylenecarbinol with a second mole of dehydro-retro-Cl9-aldehyde takes place through an organometallic Reaction. The preferred embodiment consists in responding to the dehydro-retro-O21-acetylenecarbinol Allow 2 moles of alkylmagnesine halide to act in ether. The first mole is from the Hydroxyl group bonded while the second mole reacts with the acetylene bond and makes the terminal carbon atom condensable. The dimagnesium halide compound formed it is expedient to use the same solvent with the second mole of the dehydro-retro-Cl9-aldehyde around. The condensation product is best hydrolyzed in the usual way without purification, for example by pouring it into a mixture of ice and dilute sulfuric acid, whereby the bisdehydro-retro-C40-diol described above is obtained.

In the second stage of the process according to the invention, the bisdehydro-retro-C40-diol subjected to halogenation with allyl rearrangement in inert solvents. Hydrohalic acids are suitable for this. Thereby I5, I5'-dehydrO-4, 4'-dihalogen-fl-carotene compounds educated. A preferred embodiment consists in the bisdehydro-retro-C40-diol in ethereal solution with aqueous hydrobromic acid at a temperature of -20 to + 200 treated, and after a short time the 15, 15'-dehydro-4, 4'-dibromo-fl-carotene as an orange-red powder with an absorption maximum in the ultraviolet spectrum 428 my (in petroleum ether) fails.

In the third stage of the process according to the invention are in the I5, 15'-dehydro-4, 4'-dihalo-carotene compounds the halogen atoms in usual Way replaced by oxy or acyloxy groups. This can e.g. B. by implementing the Halogen compounds with alkali salts of lower fatty acids in organic solvents take place, whereby the esters of I5, I5'-dehydro-4, 4'-dioxy-ß-carotene are formed will. In an expedient embodiment, this is I5, Is'-dehydro-4,4'-dibromo-β-carotene cooked with potassium acetate in glacial acetic acid. You can use mild alkaline saponification then from the esters of I5, I5'-dehydro-4, 4'-dioxy-carotene the I5, I5'-dehydro-4, 4'-dioxy-iS-carotene itself as a red, finely crystalline powder with two absorption maxima This compound is obtained in the ultraviolet spectrum at 430 and 458 m, t4 (in petroleum ether) consists of a mixture of stereoisomeric forms and has a blurred Melting point from I38 to I42 °. It is particularly advantageous to use the 15, 15'-dehydro-4, 4'-dihalo-ß-carotene compounds directly into the 15. 15'-dehydro-4,4'-dioxy-ß-carotene to convert.

For this purpose, in the preferred embodiment, the halogen compound in an inert solvent such as benzene with silver oxide and water at room temperature stirred well for a few hours.

Before the fourth stage of the process according to the invention, the I5, 15'-dehydro-4,4'-dioxy-ß-carotene now 15, 15'-dehydro-4,4'-dioxo-ß-carotene is oxidized will. This can e.g. B. be done so that the I5, I5'-dehydro-4, 4'-dioxy-ß-carotene in an inert solvent such as methylene chloride or chloroform with manganese dioxide is treated at room temperature or at the boiling point of the solvent.

The I5, I5'-dehydro-4, 4'-dioxo-ß-carotene forms purple crystals from melting point 186 to 188 °. This compound shows a in the ultraviolet spectrum Absorption maximum at 439 mill. (In petroleum ether). You can use the I5, I5'-dehydro-4, 4'-dioxo-fl-carotene by reduction with lithium aluminum hydride into the 15, I5'-dehydro-4, Convert 4'-dioxy-ß-carotene back. The reaction sequence of the oxidation with manganese dioxide, Crystallization of the diketo compound obtained and subsequent L * hiumaluminiumhydridreduction Can be used with advantage to purify I5, I5'-dehydro-4, 4'-dioxy-ß-carotene will.

In the fourth stage of the process according to the invention, the 4,4'-disubstituted I5, I5'-dehydro-ß-carotene compounds on the triple bond Partially hydrogenated catalytically in a manner known per se.

This is done with the help of metal catalysts and hydrogen in one organic solvent carried out. A suitable catalyst is a through Addition of lead and quinoline poisoned palladium-calcium carbonate catalyst. There is a particularly advantageous embodiment of this fourth method stage in that the hydrogenation is carried out in a hydrocarbon in which the 4,4'-disubstituted I5, I5'-dehydro-ß-carotene compounds only partially to solve. As a result, these compounds only go slowly as the hydrogenation progresses in solution; at the same time, however, the hydrogenation product from the hydrogenation mixture crystallize.

This gives 4,4'-disubstituted 15,15'-cis-β-carotenes with a characteristic maximum in the ultraviolet absorption spectrum for the cis configuration. For example, the 15'-cis-4,4'-dioxy-ß-carotene has next to the main maxima at 448 and 475 m, t there is a secondary maximum at 336 to 337 m, (in petroleum ether), which is characteristic of the cis configuration. Isolation of the hydrogenation product not necessary. The subsequent isomerization can be carried out directly with the Carry out suspension of the hydrogenation product.

In the fifth stage of the process according to the invention, the 4, 4'isubstituted I5, I5'-Cisß-Carotenes in a known manner to the trans-Verbir isomerized. This is achieved, for example, by treating with iodine Exposure or by heating. A particularly advantageous embodiment of the The method consists in that the 4,4'-disubstituted 15 Ig'-cis4-carotene compounds in an insufficient amount of an organic solvent to dissolve the substance, for example petroleum ether, benzene, etc., heated to 80 to 1000 for several hours. As isomerization progresses, the cis compounds go into solution, with at the same time the trans-compounds formed crystallize out, whereby a almost quantitative isomerization can be achieved. One gets in this way for example from 15, 15'-cis-4, 4'-dioxy-ß-carotene, the 4, 4'-dioxy-fl-carotene directly as a finely crystalline red powder that decomposes at 145 to 147 degrees melts and in the ultraviolet spectrum two maxima at 452 and 480 mµ (in petroleum ether) having. Before the isomerization, any ester groups present in the 15, 15'-cis-4, 4'-dioxy-ß-carotene can be saponified in the usual way. Furthermore can the I5, I5'-cis-4, 4'-dioxy-fi-carotene before isomerization to 15, 15'-cis-4, Oxidize 4'-dioxo-ß-carotene.

A particularly advantageous production method for the 4,4'-dioxy-ß-carotene According to the invention, dehydro-retro-Cl9-aldehyde is obtained by means of a Grignard reaction condensed with acetylenedimagnesium bromide, the bisdehydro-retro-C40-diol formed treated in ethereal solution with aqueous hydrobromic acid, on the resulting 15, I5'-dehydro-4, 4'-dibromo, 8-carotene silver oxide and water can act that obtained I5, 15'-dehydro-4, 4'-dioxyß-carotene at the triple bond with the help partially hydrogenated a palladium catalyst poisoned with lead and quinoline and the I5, 15'-cis-4, 4'-dioxy-ß-carotene formed in the form of a suspension in isomerized to 4,4'-dioxyß-carotene in an inert solvent by heating.

The process products can be separated by crystallization, solvent distribution and chromatograph purify. - By adding antioxidants, you can which can also be present during the course of the synthesis, are stabilized.

The novel compounds obtainable according to the invention, for. B. the 4, 4'-Dioxy-ß-carotene, its esters and the 4,4'-dioxo-fl-carotene are valuable Dyes, which are mainly used for coloring food and animal feed should.

Example I a) Dehydro-retro-C40-diol.

From 16 parts by weight of magnesium and 110 parts by weight of hexyl bromide a solution of hexylmagnesium bromide is prepared in 330 parts of absolute ether. The solution is stirred in an acetylene atmosphere for 24 hours. Two are formed Layers. The upper layer is separated off and the lower layer is washed once with 100 Parts of space ether.

Then add 200 parts of the volume of ether and quickly let a solution of 80 parts by weight of 8- [2 ', 6', 6'-trimethylcyclohexen- (2 ') -ylidene- (r') -2, Add dropwise 6-dimethyloctatriene- (2, 4, 6) -al- (I) in 200 parts by volume of ether.

The mixture is refluxed for 3 Sturiden with stirring in one Nitrogen atmosphere. After cooling, the reaction mixture is poured into 75 parts by weight Ammonium chloride and 175 weight share ice and stir for 10 minutes well done. The ethereal solution is then washed three times with 200 parts by volume of water each time. After drying over sodium sulfate and evaporation of the ether, 87 parts by weight are obtained yellow resinous I, I8-di- [2 ', 6', 6'-trimethylcyclohexen- (2 ') - ylidene- (I')] - 3, 7, I2, I6-tetramethyl-8, II-dioxy-octadecahexaen- (2, 4, 6, I2, 14,16) -in- (9) with with an absorption maximum in the ultraviolet spectrum at 349.5 mµ in petroleum ether. b) 15, 15'-dehydro-4, 4'-dibromo-ß-carotene 10 parts by weight 1, 18-di- [2 ', 6', 6'-trimethylcyclohexen- (2 ') - ylidene- (1')] - 3,7,12,16-tetramethyl-8,11-dioxy-octadecahexaen- (2, 4, 6, I2, I4, I6) -in- (g) in 80 parts by volume of ether at 0 ° with thorough stirring 4 spaces of 60% aqueous hydrobromic acid were added within 2 minutes and the mixture was stirred for a further 10 minutes at 0 °. Thereupon the product filtered off and washed with ether and water. The 15,15'-dehydro-4 formed, 4'-dibromos-carotene has an absorption maximum at 430 in the ultraviolet spectrum mµ (in petroleum ether). Fuzzy melting point at 120 °. c) 15, 15'-dehydro-4, 4'-dioxy-ß-carotene 6 parts by weight of I5, I5'-dehydro-4, 4'-dibromo-ß-carotene dissolved in 180 parts by volume of benzene and with 6 parts by weight of silver oxide and 60 parts by volume Water shaken in a carbon dioxide atmosphere at room temperature for 4 hours. The silver oxide is filtered off and the benzene solution is evaporated after drying Sodium sulfate. The 15, 15'-dehydro-4, 4'-dioxy-ß-carotene can be obtained from ether-petroleum ether and redissolve methylene chloride-methanol. It melts out of focus between I38 and r42 ° and has two maxima in the ultraviolet spectrum at 430 and 458 mµ (in petroleum ether) on. d) 15, 15-cis-4, 4'-dioxy-, 8-carofin 100 parts by weight of 15, 15'-dehydro-4, 4'-dioxy-β-carotene in 5000 parts by volume of toluene, 30 parts by weight of Lindlar catalyst (Helvetica Chimica Acta, Vol. 35 I952, 5. 446) and o, oos volume quinoline at 200 in one Shaken hydrogen atmosphere until 1 mol of hydrogen is absorbed.

After filtering off the catalyst, the filtrate is in a high vacuum evaporated. The 15,15'-cis-4,4'-dioxy-fl-carotene shows in the ultraviolet spectrum Maxima at 336 to 337, 448 and 475 m, u in petroleum ether; F. = 110 to III. e) 4, 4'-Dioxy-ß-carotene I part by weight I5, 15'-cis-4, 4'-Dioxy-ß-carotene is 3 parts by volume Petroleum ether (boiling point 70 to 100 °) for 12 hours at 80 ° in a carbon dioxide atmosphere warmed up. It is then filtered. The 4,4'-dioxy-fl-carotene formed can be obtained from methylene chloride petroleum ether or methylene chloride-methanol are redissolved. It represents a finely crystalline red Powder, which in the ultraviolet spectrum at 452 and 480 m, z two absorption maxima (in petroleum ether) and melts at I45 to I47 ° with decomposition.

Example 2 Dehydro-retro-C40-diol One passes into a solution of 3 Parts by weight of lithium in 1200 parts by volume of liquid ammonia to complete Implementation of dry, acetone-free acetylene. Then add while stirring vigorously within 20 minutes a solution of 100 parts by weight of 8- [2 ', 6', 6'-trimethylcyclohexen- (2 ') -yliden- (1')] - 2, Add 6-dimethyloctaftien- (2, 4, 6) -al- (I) in 400 parts of volume to absolute ether and stir the reaction mixture vigorously for 20 hours with exclusion of moisture. Thereon 50 parts by weight of ammonium chloride are added in small portions and the ammonia is left evaporate. After adding 400 parts by volume of water, the ether layer is separated off, washed with water, dried with sodium sulfate and concentrated. The one left behind reddish oil is sharply dried in vacuo. 108 parts by weight of Io- [2 ', 6 ', 6'-Trimethylcyclohexen- (2') - yliden- (1 ')] - 4, 8-dimethyldecatriene- (4, 6, 8) -in- (1) -ol- (3), which in the ultraviolet spectrum has an absorption maximum at 349 mμ in petroleum ether.

The product is dissolved and closed in 500 parts of the volume of absolute ether one of 18 parts by weight of magnesium, 91 parts by weight of ethyl bromide and 300 parts by volume Grignard solution prepared with absolute ether with stirring at 15 to 200 gradually admitted. The mixture is then heated in a nitrogen atmosphere for 1 hour reflux, cool it with ice water, add a solution of 92 at about 200 Parts by weight of 8- [2 ', 6', 6'-trimethylcyclohexen- (2 ') - ylidene- (r') l-2,6-dimethyloctatriene- (2, 4, 6) -al- (r) in 400 room parts. absolute ether and the mixture is still heated 3 to 4 hours under reflux in a nitrogen atmosphere. The obtained reaction solution is to a mixture of 400 parts by volume of 3 n-sulfuric acid and 600 parts by weight Poured ice, separated the ethereal layer, with 5% sodium bicarbonate solution washed, dried with sodium sulfate and evaporated in vacuo. You get 200 Parts by weight of resinous 1,18-doi- [2 ', 6', 6'-tert-methylcyclohexen- (2 ') - ylidene- (1')] -3, 7, 12, 16-tetramethyl-8, II-dioxyoctadecahexaen- (2, 4, 6, I2, I4, I6) -in- (9), the is processed according to Example 1.

Example 3 15, 15'-Dehydro-4,4'-diacetoxy-ß-carotene I part by weight I5, I5'-dehydro-4,4'-dibromo-ß-carotene (obtained according to Example 1) is divided into 15 parts Glacial acetic acid with 2 parts by weight of anhydrous potassium acetate for 2 hours in a carbon dioxide atmosphere heated to 1000. The mixture is diluted with water, extracted with ether and the ether solution was washed three times with water and dilute sodium bicarbonate solution. After drying and evaporation of the ethereal solution, the 15, r5'-dehydro 4, 4'-diacetoxy-ß-carotene as a red, viscous resin, which is obtained by recrystallization from methylene chloride-methanol is cleaned; Melting point 104 to 1220; Ultraviolet maxima at 430 and 454 with (in petroleum ether).

This compound can either lead to I5, I5'-dehydro-4, 4'-dioxy-ß-carotene hydrolyzed and then according to Example 1 processed further or analogously Example I, d) and e) are converted into 4,4'-diacetoxy-fl-carotene; F. = I5I to 1530.

Example 4 15, 15'-Dehydro-4,4'-dioxo-β-carotene.

6 parts by weight of crude I5, I5'-dehydro-4, 4'-dioxyp-carotene dissolved in 200 parts by volume of methylene chloride and after adding 70 parts by weight of manganese dioxide shaken under nitrogen for 12 hours. After filtering and concentrating the reaction solution the residue is taken up in benzene and treated with low-boiling petroleum ether, until crystallization begins. By redissolving the crystals obtained from methylene chloride-petroleum ether, purple needles are obtained; Melting point I86 to 188 "; ultraviolet maximum at 439 mµ (in petroleum ether). This compound can analogously to example, d) and e) are converted into 4,4'-dioxo-ß-carotene; F. = 208 by 2090.

Example 5 15, 15'-dehydro-4,4'-dibromo-fl-carotene 75 parts by weight crude I, I8-di- [2 ', 6', 6'-trimethylcyclohexen- (2) -ylidene- (1 ')] - 3, 7, I2, I6-tetramethyl-8, II-dioxyoctadecahexaen- (2, 4, 6, I2, I4, I6) -in- (g) (obtained according to Example I) are dissolved in 350 parts by volume of dry ether and in a nitrogen atmosphere with stirring at 0 to 5 ° within 30 minutes with a mixture of 10 parts by volume Phosphorus tribromide and 100 parts by volume of ether added. After the addition is complete, stir if the mixture is continued for about 2 hours at 0 °, the red precipitate is then sucked off off, washes it with cold ether and dries it in a vacuum at 400. This gives about 42 parts by weight of 4,4'-dibromo-15, 15'-dehydro-carotene with a broad absorption maximum at 430 to 432 m, u.

Claims (6)

P A T E N T A N S P R Ü C H E: I. Process for the production of 4, 4'-disubstituted ß-Oarotinen, characterized in that acetylene in known per se by an organometallic reaction on both sides with 8- [2 ', 6 ', 6'-Trimethylcyclohexen- (2') - yliden- (1 ')] - 2, 6-dimethyloctatriene- (2, 4, 6) -al- (I) condensed, the formed I, 18-di- [2 ', 6', 6'-trimethylcyclohexen- (2 ') - ylidene- (1')] - 3, 7, I2, I6-tetramethyl-8, II-dioxyoctadecahexaen- (2, 4,6,12,14, I6) -in- (9) one Subjected to halogenation with allyl rearrangement, in the resulting I5, I5'-dehydro-4, 4'-dihalo-ß-carotene the halogen atoms in the usual way by oxy or acyloxy groups replaced; the obtained 15, 15'-dehydro-4,4'-dioxy-β-carotene, optionally esterified in the 4,4'-position on the triple bond catalytically partially hydrogenated and in a manner known per se the 15, I5'-cis-4, 4'-dioxy-ß-carotene formed isomerized in a known manner, whereby the acyloxy groups are converted into oxy groups before the hydrogenation or the isomerization saponify and / or oxidize the oxy groups to oxo groups. 2. The method according to claim I, characterized in that either Acetylenedimagnesium halide with twice the molar amount of 8- [2 ', 6', 6'-trimethylcyclohexene (2 ') - yliden- (1')] - 2, 6-dimethyloctatriene- (2, 4, 6) -al- (I) condensed or that one first lithium acetylide in liquid ammonia with 1 mole of 8- [2, 6 ', 6'-trimethylcyclohexen- (2') - ylidene- (1 ')] - 2, 6-dimethyloctatriene- (2, 4, 6) -al- (I) condensed, the condensation product formed hydrolyzed and the obtained io- [2 ', 6', 6'-trimethylcyclohexen- (2 ') - ylidene- (I')] - 4, 8-dimethyldecatrien- (4, 6, 8) -in- (I) -ol- (3) by means of a Grignard reaction with a second mole of 8- [2 ', 6', 6'-trimethylcyclohexen- (2 ') - ylidene- (1')] - 2,6-dimethyloctatriene- (2, 4, 6) -al- (I) condensed. 3. The method according to claim I, characterized in that as Halogenating agent hydrohalic acid is used. 4. The method according to claim I, characterized in that the Halogen atoms in I5, I5'-dehydro-4, 4'-dihalo-ß-carotene through oxy groups Treat with silver oxide and water replaced. 5. The method according to claim I, characterized in that one Suspension of 4,4'-disubstituted 15,15'-dehydro-, 8-carotene in a hydrocarbon Partially hydrogenated catalytically at room temperature. 6. The method according to claim I, characterized in that the Isomerization of the 15,15'-cis-4,4'-disubstituted β-carotene formed Heating a suspension of the same in an inert solvent such as petroleum ether, performs.