Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1997-03-24
1998-05-26
Lilling, Herbert J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
562571, C07C22700, C07C22900, C07C22706, C07C22924
Patent
active
057568391
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for preparing D,L-aspartic acid by heating aqueous solutions of ammonium salts of maleic acid at elevated temperatures under pressure, acidifying the reaction solution to liberate D,L-aspartic acid and isolating the D,L-aspartic acid.
DISCUSSION OF THE BACKGROUND
DE-A-2 029 502 discloses the preparation of D,L-aspartic acid by heating aqueous solutions of the diammonium salt of maleic acid at from 110.degree. to 145.degree. C. under from 2 to 5 bar. The aqueous solution of the diammonium salt of maleic acid is prepared by neutralizing an aqueous solution of maleic acid with aqueous ammonia at not above 20.degree. C., the pH of the ammonium salt solution being 7.5. The reaction solution obtainable in this way is acidified with strong mineral acids, such as hydrochloric acid, until the pH is 3 in order to liberate the aspartic acid from the monoammonium salt which is initially formed. According to the example in the application, the yield of D,L-aspartic acid after recrystallization from water is 61% of theory. However, the space-time yields are unsatisfactory.
D,L-aspartic acid is prepared by the process disclosed in DD-A-126 075 by preparing the diammonium salt of maleic acid in a conventional way by neutralizing maleic anhydride with aqueous ammonia, evaporating it under atmospheric pressure up to 115.degree. C., adding a carboxamide as catalyst and further evaporating the resulting aqueous solution under atmospheric pressure up to 120-130.degree. C., and stirring the reaction mixture at this temperature for 16 hours. It is then cooled to 80.degree. C., hydrochloric acid is added, and the mixture is refluxed in order to destroy the catalyst. The excess hydrochloric acid is then distilled off under reduced pressure, the residue is taken up in water, and the aspartic acid is precipitated by adjusting the solution to pH 2.8. The yield of D,L-aspartic acid after recrystallization is 63%.
JP-A-25 133/65 discloses the preparation of D,L-aspartic acid by reacting maleic acid with ammonia in the presence of ammonium compounds such as ammonium chloride or ammonium acetate. The aspartic acid is liberated from its ammonium salt by adding maleic acid to the reaction solution. This entails adjustment of the pH to 2.5-3. The D,L-aspartic acid which results in crystalline form is filtered off with suction, and the mother liquor, which contains ammonium maleate, is reused.
U.S. Pat. No. 4,560,653 discloses the preparation of L-aspartic acid by enzymatic addition of ammonia onto fumaric acid. L-aspartic acid is precipitated from the resulting ammonium L-aspartate solution by adding maleic acid. The mother-liquor remaining after removal of L-aspartic acid is subjected to an isomerization step in which maleic acid is converted into fumaric acid, subsequently purified and then recycled to the enzymatic addition.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for preparing D,L-aspartic acid which provides higher yields of D,L-aspartic acid than known processes.
We have found that this object is achieved by a process for preparing D,L-aspartic acid by heating aqueous solutions of ammonium salts of aspartic acid at elevated temperatures under pressure, acidifying the reaction solution to liberate D,L-aspartic acid and isolating the D,L-aspartic acid, when maleic acid and ammonia are reacted in a molar ratio of from 1:2.1 to 1:50 in aqueous solution at from 60.degree. C. to 250.degree. C. under pressures of at least 1 bar, the pressure being controlled during the reaction in such a way that the reaction mixture is almost entirely in the liquid phase.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In contrast to the prior art processes, in the process according to the invention the reaction of ammonium salts of maleic acid in aqueous solution is carried out in such a way that the reaction solution is virtually quantitatively in the condensed phase under the reaction conditions. This ensures that the concentration of
REFERENCES:
patent: 4560653 (1985-12-01), Sherwin et al.
patent: 4963672 (1990-10-01), Merger et al.
patent: 5541090 (1996-07-01), Sakano et al.
Derwent Orbit Abstract 77-57662y/33 Abs DD-126075 (Jun. 15, 1977) Berlin Chemie Veb.
Derwent Orbit Abstract 77-01621T/02 Abs DE 2029502 (Feb. 1972) Lentia GmbH Chem.
Aps Abstract Japan 07-247251 (Sep. 26, 1996) Fujii et al.
Bazner Rudolf
Kratz Detlef
Kroner Matthias
Pressler Uwe
Witzel Tom
BASF - Aktiengesellschaft
Lilling Herbert J.
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