Preparation of vitamin E

Details Preparation of vitamin E Preparation of vitamin E

1994-09-09

1995-11-21

Chan, Nicky

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

549410, C07D31172

Patent

active

054688833

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/EP93/00498 filed Mar. 5, 1993.
The present invention relates to an improved process for preparing vitamin E by acid-catalyzed reaction of 2,3,5-trimethylhydroquinone (TMH) with a phytol.
The preparation of dl-.alpha.-tocopherol (vitamin E) by reacting TMH and a phytol, for example isophytol (IP), at elevated temperature in a solvent of low polarity in the presence of various acid catalysts has been disclosed.
According to statements in Chem. Abstracts. (C.A.) 84 (1976) 59792 and C.A. 85 (1976) 46898, it is possible to carry out the reaction in the presence of SiO.sub.2 /Al.sub.2 O.sub.3 with acids.
According to C.A. 73 (1970) 77483, C.A. 80 (1974) 3385, C.A. 80 (1974) 3386, C.A. 73 (1970) 98799 and DE-A 22 08 795, the reaction can also be carried out in the presence of ZnCl.sub.2 together with acids such as hydrohalic acids, especially HCl, trichloroacetic acid or acetic acid.
According to the statements in DE-A 22 08 795 it is also possible to use ZnCl.sub.2 mixed with NaHSO.sub.4, sulfuric acid or p-toluenesulfonic acid in a molar ratio of from 1:3 to 1:1.
According to the statements in C.A. 84 (1976) 74471, the reaction can be carried out in the presence of a mixture of SiO.sub.2 and Al.sub.2 O.sub.3 in the ratio 87:13 as catalyst in perchloroethylene.
According to U.S. Pat. No. 3,459,773, vitamin E is obtained by reacting phytol or isophytol with TMH in an inert solvent using a macroreticular cation exchanger resin of the sulfonic acid type.
It is common to all these known processes that the vitamin E cannot be prepared in the required purity on the industrial scale.
To overcome this problem, the reaction disclosed in DE 27 43 920 is carried out in the presence of a mixture of silica and alumina or silica gel and zinc chloride and a strong acid such as concentrated HCl, H.sub.2 SO.sub.4, H.sub.3 PO.sub.4 or p-toluenesulfonic acid.
The disadvantages of this process are, as with many of the abovementioned processes, that problems with corrosion arise, and that the wastewater may be polluted with zinc ions.
It is an object of the present invention to find a catalyst system for reacting TMH and phytol or isophytol to give vitamin E which can be used to prepare vitamin E more advantageously than in the prior art, even on a relatively large scale. It was necessary for this that the catalyst system is not toxic (like BF.sub.3 adducts), that it is not corrosive (like ZnCl.sub.2, HCl, HCOOH and H.sub.3 PO.sub.4), that it suppresses as far as possible unwanted side reactions such as dehydration of isophytol to phytadienes, and that it catalyzes reaction of the costly and sensitive starting materials in high yield, even when equimolar amounts are used, since the excess starting materials can be separated from the reaction product only at great expense.
We have found that this object is achieved by using a mixture of ortho-boric acid on the one hand and certain dicarboxylic acids, such as oxalic acid or tartaric acid, or a tricarboxylic acid, such as citric acid, on the other hand, in particular a mixture of ortho-boric acid and oxalic acid, which meets the stated requirements by far the best. Catalysis of the reaction by each of the components alone is inadequate. The optimal result is made possible only by the unexpected synergistic effect.
The invention accordingly relates to an improved process for preparing dl-.alpha.-tocopherol or dl-.alpha.-tocopheryl acetate by acid-catalyzed reaction of 2,3,5-trimethylhydroquinone with phytol or isophytol in a solvent at elevated temperature, with or without subsequent esterification of the resulting tocopherol with acetic anhydride, wherein the reaction is carried out in the presence of a mixture of ortho-boric acid on the one hand and oxalic acid, tartaric acid or citric acid on the other hand.
The preparation of TMH and phytol or isophytol is known and therefore does not need to be discussed.
The process takes place particularly advantageously when oxalic acid or tartaric acid, especially oxalic acid, mixed with ortho-boric acid is used

REFERENCES:
patent: 3459773 (1969-08-01), Moroe et al.
patent: 3708505 (1973-01-01), Greenbaum et al.
patent: 4217285 (1980-08-01), Yoshino et al.
Chem. Abstr., 84(1976) 59792X.
Chem. Abst. 73(1970) 77483z.
Chem. Abst. 84(1976)74471k.

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