GB1568559A - Manufacture of tocopherol - Google Patents

Abstract

Tocopherol is prepared by reacting 2,3,5-trimethylhydroquinone with isophytol or phytol. The reaction is carried out in the hydrocarbon solvent in the presence of zinc chloride and proton donors. Before the reaction the isophytol or phytol is treated at room or elevated temperature with small amounts of ammonia or with a primary or secondary aliphatic, cycloaliphatic or araliphatic amine. The isophytol used can be prepared by catalytic hydrogenation of dehydroisophytol in the presence of an amine.

Description

(54) MANUFACTURE OF TOCOPHEROL (71) We, BASF AKTIENGESELL SCHAFT, a German Joint Stock Company of 6700 Ludwigshafen, Federal Republic of Germany, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement:- The present invention relates to an im proved process for the manufacture of toco pherol by reacting 2,3,3-trimethyihydro- quinone with isophytol or phytol in the presence of zinc chloride and a proton donor, For example hydrogen chloride.

The reaction of trimethylhydroquinone with isophytol in heptane as the solvent in the presence of zinc chloride or other Lewis acids and hydrochloric acid gas or other proton donors at 1000 Under atmospheric pressure, to give d,lçtocopherol (vitamin E) has been disclosed. It is true that this process can be carried out relatively simply, but both the yield and the purity of the end product required improvement.

Attempts have therefore already been made to carry out the reaction in accordance with German Laid-Open Application DOS 1,909,164, using a boron trifluoride complex or aluminum bichloride complex of trimethylhydroquinone at a lower temperature.

Iron powder, or iron-II chloride and hydrogen chloride, have also already been proposed, in German Laid-Open Application 2,160,103.

However, with these processes it was only possible to improve either the purity or the yield.

The present invention seeks to improve the yield of the condensation process which is industrially the simplest to carry out, i.e. the process using zinc chloride and hydrogen chloride, and simultaneously to improve the purity of the end products.

The present invention provides a process for the manufacture of tocopherol by reacting 2,3,5 - trimethylhydroquinone with isophytol or phytol in the presence of zinc chloride and a proton donor in a hydrocarbon as the solvent, wherein the reaction is carried out with isophytol or phytol which has been previously contacted, with ammonia or a primary or secondary aliphatic, cycloaliphatic or araliphatic amine at a normal or elevated temperature, especially at from 20 to 2000 C.

Surprisingly, processes according to the invention are able to give a better yield of tocopherol with the formation of less byproducts.

As a rule, the contacting is carried out with small amounts of ammonia or amine exceeding 100 ppm, e.g. with from 0.05 to 5, preferably from 0.1 to 2, per cent by weight of ammonia or amine, based on isophytol or phytol. Even higher amounts of ammonia or amine can also be used, but this does not result in any further advantage. If amounts greater than 0.5 per cent by weight are used, it is advisable to remove the excess, before continuing the reaction, by distillation under atmospheric pressure or reduced pressure.

The contacting with the amine or ammonia is advantageously carried out by mixing the latter with isophytol or phytol and heating the mixture, e.g. at from 20 to 2000 C., preferably from 50 to 1200 C. The contacting may alternatively be carried out at below 20 G, but this increases the duration of the contacting substantially, and it is advisable to use solvents, because of the viscosity of phytol or isophytol at low temperatures. For this reason, it is technically advantageous to carry out the process at a slightly elevated temperature. The contacting according to the invention can also be carried out at above 200 C., e.g. at up to 2200 C., if the heating is kept sufficiently brief to avoid decomposition of the phytol or isophytol. Accordingly, the limit imposed on the contacting temperature is essentially the temperature at which significant decomposition of phytol or isophytol commences. The ammonia or amine may be added undiluted or as a solution in a solvent, e.g. heptane.

Depending on the temperature chosen, the chosen duration of contacting may be from a few seconds to 100 hours. A duration of from one to 15 hours at from 50 to 1000 C. is pre ferred if the contacting is carried out batchwise. It is also possible to heat the isophytol or phytol, mixed with the amine, to from 60 to 1800 C., preferably from 90 to 1300 C., in a heating zone with a residence time of from 30 minutes down to 0.3 minute, and to feed the hot isophytol or phytol directly to the main reaction for formation of tocopherol.

The contacting with ammonia may be carried out in the same manner as that described for the amines, but the use of the amines is preferred, because they are more effective.

The isophytol, previously contacted with ammonia or an amine, which is employed as one alternative starting material in the process may also be a product obtained by catalytic hydrogenation of dehydroisophytol in the presence of an amine or ammonia.

Examples of amines are aliphatic, cyclo aliphatic and araliphatic amines of 1 to 20 carbon atoms in the chain. Amongst these, the primary alkyl monoamines, which may have straight or branched chains, are preferred.

Specific examples of aliphatic amines which may be used are isopropylamine, n-butylamine, iso-butylamine, diethylamine and especially monomethylamine, stearylamine and tridecyl amine (an isomer mixture obtained from tetrameric propylene via a mixture of alcohols of 13 carbon atoms). An example of a cycloaliphatic amine which may be used is cyclo hexylamine, whilst benzylamine is an example of a araliphatic amine which may be used.

The amine to be used may contain one or more further substituents, e.g. hydroxyl, alkoxy or alkylamino groups. Specific examples of suitable compounds are monoethanolamine and 3 -dimethylamino- 1-propylamine.

The reaction of the isophytol or phytol with trimethylhydroquinone may be carried out by conventional methods at from 60 to 2000 C., especially from 80 to 1400 C. and preferably from 90 to 110 C., in hydrocarbons, e.g. toluene, xylene, octane, hexane, decane and especially n-heptane, as the solvent. The amount of solvent can be varied within wide limits and may be from one to ten parts by weight per part by weight of isophytol or phytol. The amount of zinc chloride can be from 0.04 part by weight, per pan by weight of isophytol or phytol, up to very large amounts, of 0.5 part by weight or even more, though such large amounts offer no advantage.

Proton donors which are particularly suitable are aqueous acids, e.g. concentrated hydrochloric acid and concentrated hydrobromic acid, or strong mineral acids, e.g. sulfuric acid or sodium bisulfate, as described in German Laid-Open Application 2,208,795. Amongst these proton donors, hydrochloric acid is pre fs Tolnenesulfonic acid, and mixtures of the acids mentioned, may also be used.

The water produced by the reaction may be removed from the reaction mixture, but the conversion to d,lFa-tocopherol can also be effected without such removal of water.

Instead of using aqueous hydrochloric acid, hydrogen chloride gas, which is passed into the reaction mixture during the reaction, may equally well be employed. It has the advantage that the acid concentration cannot rise too high, since excess hydrogen chloride gas volatilizes from the reaction mixture. In contrast, a highboiling acid, e.g. sulfuric acid, may favor the formation of by-products if it is present in too high a concentration.

The mechanism of action involved in the preliminary contacting with amine is unknown and has hitherto defied elucidation. The preliminary contacting of the isophytol or phytol with amine particularly prevents the formation of higher-boiling impurities during the synthesis of tocopherol. However, the amount of impurities boiling slightly below tocopherol acetate is also reduced. Accordingly, the preliminary contacting of isophytol with amine results in a purer vitamin E, in higher yield.

In the specific Examples of the present invention which follow, parts are by weight and bear the same relation to parts by volume as that of the liter to the kilogram. As can be seen from Examples 1 to 4 the crude tocopherol can be converted to tocopherol acetate by reaction with acetic anhydride to assist in isolation.

EXAMPLE 1.

1 part of crude isophytol of 95% purity,. corresponding to 0.95 part of isophytol, is mixed with 0.002 part of methylamine whilst stirring and the mixture is heated at 900 C. for 3 hours. After cooling, the isophytol is used directly for condensing with trimethylhydroquinone.

The amine-contacted isophytol is added dropwise in the course of one hour, whilst stirring, to a boiling mixture of 2.4 parts by volume of n-heptane and 0.08 part of zinc chloride and 0.49 part of trimethylhydroquinone. Hydrogen chloride gas is passed through the mixture in an amount such that the mixture remains just saturated. This is achieved by ensuring that a little hydrogen chloride escapes, partially entraining the water produced, in accordance with the vapor pressure. After cooling the reaction mixture, the latter is extracted with 10 parts of a 50% strength methanol/water mixture to remove excess trimethylhydroquinone and zinc chloride.

The heptane solution which remains is concentrated to dryness, 0.48 part of acetic anhydride is added to the residue, i.e. to tne crude tocopherol, the mixture is boiled for 4 hours under reflux and the unconverted acetic anhydride and the acetic acid formed are distilled off. The tocopherol acetate which re mains is distilled under reduced pressure. The fraction which boils at 180215 G/0.001 mm Hg is d,le-tocopherol acetate and is separated off. 1.45 parts of vitamin E acetate of 93% purity are obtained, corresponding to a content of impurities of 7%, measured by means of gas chromatography, with an internal standard.

The yield of pure vitamin E acetate is accordingly 88.5% of theory, based on trimethylhydroquinone employed.

EXAMPLE 2.

One part of crude isophytol, of 95% purity, corresponding to 0.95 part of isophytol, is mixed with 0.002 part of monomethylamine and the mixture is heated at 1500 C. for one minute. The further reaction to give vitamin E is carried out as described in Example 1.

1.42 parts of vitamin E of 93.5% purity are obtained. The yield of pure vitamin E acetate is 87.2% of theory, based on trimethylhydro quinone employed.

EXAMPLE 3.

One part of crude isophytol of 95% purity, corresponding to 0.95 part of isophytol, is mixed with 0.002 part of monomethylamine and this mixture is kept for 3 days at 300 C The further redaction, to give vitamin E, is carried out as described in Example 1. 1.46 parts of vitamin E of 92% purity are obtained.

The yield is 88.7% of theory.

EXAMPLE 4.

One part of dehydroisophytol is mixed with 0.0029 part by weight of monomethylamine.

After adding 0.02 part by weight of catalyst, containing 0.7% of palladium and 3% of zinc on calcium carbonate as a carrier, hydrogenation is carried out for from 12 to 16 hours at 60 C. and 1 atmospheric gauge hydrogen pressure. After one mole of hydrogen has been taken up per mole of dehydroisophytol, the hydrogenation is discontinued, the catalyst is filtered off and the isophytol is converted to d,lvg-tocopherol acetate as described in Example 1. d,1-α-Tocopherol acetate, of 93.5% purity as measured by means of gas chromatography, with an internal standard, is obtained in a yield of 89% of theory.

EXAMPLES 5 TO 18.

One part of crude isophytol of 95% purity, corresponding to 0.95 part of isophytol, is mixed with the amount, shown in column 3, of an amine from the Table which follows, and this mixture is kept at the temperature shown in column 5 for the period shown in column 4. The further working up to give vitamin E is carried out as described in Example 1, but the distillation of the d,l < -tocopherol acetate is dispensed with and the content of d,l-a- tocopherol acetate is determined by gas chromatography. Crude d,l < -tocopherol acetate is obtained in the yield shown in column 6, and in the purity shown in column 7. The yield is calculated as pure d,lfir-tocopherol acetate, based on trimethylhydroquinone employed.

TABLE 1 2 3 4 5 6 7 Amount of amine, parts per Period of part of treatment Treatment Yield, crude with amine temperature % of Purity, Example Amine isophytol hours C theory % 5 Blank experiment, without amine - - - 80.6 80.4 6 n-butylamine 0.002 5 100 86.8 87.0 7 2-butylamine 0.0045 5 100 82.4 83.4 8 iso-butylamine 0.0045 5 100 86.3 86.3 9 n-propylamine 0.0033 5 100 86.7 85.7 10 isopropylamine 0.0033 5 100 84.1 83.3 11 cyclohexylamine 0.006 5 100 85.7 84.9 12 stearylamine 0.017 5 100 91.5 89.5 13 benzylamine 0.007 5 100 85.9 86.2 14 mono-2-ethylhexylamine 0.0083 5 100 85.8 86.1 15 3-dimethylamino-1-propylamine 0.0065 5 100 80.0 82.0 16 monoethanolamine 0.004 5 100 83.8 84.4 17 diethylamine 0.0047 5 100 83.0 82.5 18 tridecylamine 0.013 5 100 91.2 88.7 EXAMPLE 19.

One part of phytol is mixed with 0.002 part of monomethylamine and this mixture is kept at 1000 C. for 5 hours. The further reaction to give vitamin E is carried out as described in Example 1, but the distillation of the crude d,la-tocopherol acetate is dispensed with and the amount of product and its purity is determined by gas chromatography An 80% yield of d,l-tocopherol acetate is obtained, the undistilled product being 81% pure, as determined by gas chromatography.

If the phytol is employed without preliminary contacting with amine, a 77% yield of d,la-tocopherol acetate is obtained and the purity of the undistilled product is 76%.

Claims (13)

WHAT WE CLAIM IS:

1. A process for the manufacture of tocopherol by reacting 2,3,5-trimethylhydroquinone with isophytol or phytol in the presence of zinc chloride and a proton donor in a hydrocarbon as the solvent, wherein the reaction is carried out with isophytol or phytol which has been previously contacted with ammonia or a primary or secondary aliphatic, cycloaliphatic or araliphatic amine at normal or elevated temperature.

2. A process as claimed in claim 1, wherein the reaction with 2,3,5-trimethylhydro- quinone is carried out with isophytol or phytol which has been previously contacted at from 200 C. to 2000 C.

3. A process as claimed in claim 1 or 2, wherein the isophytol or phytol has been previously contacted with a low molecular weight aliphatic primary monoamine.

4. A process as claimed in daim 3, wherein the primary monoamine is monomethylamine.

5. A process as claimed in claim 1 or 2, wherein the isophytol or phytol has been previously contacted with a primary higher fatty amine.

6. A process as claimed in claim 5, wherein the primary higher fatty amine is stearylamine.

7. A process as claimed in claim 5, wherein the primary higher fatty amine is tridecylamine.

8. A process as claimed in any of claims 1 to 7, wherein the isophytol or phytol has been previously contacted with from 0.05 to 5 per cent by weight of an amine, based on the weight of isophytol or phytol.

9. A process as claimed in any of claims 1 to 8, wherein the 2,3,5-trimethylhydroquinone is reacted with isophytol which has been manufactured by catalytic hydrogenation of dehydroisophytol in the presence of an amine.

10. A process as claimed in any of claims 1 to 9, wherein hydrochloric acid is employed as the proton donor.

11. A process for the manufacture of tocopherol carried out substantially as described in any of the foregoing Examples 1 to 4 or 6 to 19.

12. Tocopherol when manufactured by a process as claimed in any of claims 1 to 11.

13. Tocopherol acetate made from tocopherol claimed in claim 12 by reaction with acetic anhydride.