Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1998-09-01
2000-10-31
Peselev, Elli
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C07C31500
Patent
active
061405361
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for the isolation of 2-hydroxy-4-methylthiobutyric acid (MHA), whereby MHA is isolated from a reaction mixture obtained by addition of hydrogen cyanide (HCN) to methylmercaptopropionaldehyde (MMP) and hydrolysis by sulphuric acid of the methylmercaptopropionaldehyde cyanohydrin (MMP-CH) thus obtained, the reaction mixture being brought into contact in a liquid/liquid extraction system with an organic solvent substantially immiscible with water, in order to form an extraction solution which contains the solvent and the MHA transferred out of the reaction mixture, and the MHA is isolated as the extract from this extraction solution by evaporation.
2-hydroxy-4-methylthiobutyric acid (MHA) is the hydroxy analogue of the essential amino acid methionine in racemic form and, like this acid, is an important additive in animal nutrition. In the rearing of poultry MHA exhibits growth-stimulating properties similar to those of the amino acids known for this. This additive is also becoming of increasing interest in other areas of animal nutrition.
MHA is mostly used in the form of aqueous concentrates containing, in addition to the monomer, a certain proportion of oligomers, mainly the dimeric and trimeric linear ester acids. The content of these oligomers is dependent on the conditions of preparation and on the concentration chosen. Owing to their lower nutritive efficiency and the unfavourable influence on the flow properties as a result of an increase in viscosity, it is however desirable to maintain their percentage as low as possible. Commercially available formulations having a total concentration of 88 to 90 wt. % contain up to 24 wt. %, corresponding to about 27 mol %, in total of oligomers, corresponding to a ratio of monomer to oligomers of about 3:1.
The general method for the preparation of MHA proceeds from 3-methylpropionaldehyde, also referred to as methylmercaptopropionaldehyde or MMP, which is reacted with hydrogen cyanide to form 2-hydroxy-4-methylthiobutyronitrile, also referred to as MMP cyanohydrin or MMP-CH (equation I). ##STR1##
The MMP cyanohydrin formed is then hydrolysed, generally by strong mineral acids such as sulphuric acid or hydrochloric acid, via the intermediate step involving the formation of 2-hydroxy-4-methylthiobutyramide, also referred to as MHA amide (equation II) ##STR2## to prepare the methionine hydroxy analogue (MHA) (equation III). ##STR3##
This hydrolysis may be carried out either in one step or in two steps. Here, by "steps" it is meant that mineral acid and/or water is added either once or twice in order to hydrolyse the MMP-CH, that is, the number of steps corresponds to the number of addition procedures.
BACKGROUND OF THE INVENTION
The following publications are cited as being close prior art:
A similar type of method for the isolation of MHA is known, for example, from D1. D1 employs two-step hydrolysis using sulphuric acid in order to isolate MHA in liquid form as a highly-concentrated aqueous solution.
According to D1, MHA is obtained after the hydrolysis reaction, which is carried out via the amide step using excess mineral acid under specified conditions of concentration and temperature, by means of a solvent extraction wherein use is made of certain solvents which are partially miscible with water.
According to the information in D1, the characterising feature of the method described in that document is to be seen in the isolation of MHA from the extraction solution, which is carried out in such a way that the isolation includes the removal of the organic solvent in the presence of at least about 5 wt. % of water, referred to the remaining extract (MHA). MHA is isolated from the extraction solution by distillation (see Examples), with steam distillation being preferred. As a result of removing the solvent from the extraction solution during the steam distillation, the discharge obtained is a mixture of MHA and water. The steam distillation is therefore carried out in such a way that the discharge contai
REFERENCES:
patent: 5847207 (1988-12-01), Suchsland et al.
Hafner Volker
Hasseberg Hans Albrecht
Hasselbach Hans Joachim
Heinzel Harald
Huthmacher Klaus
Degussa-Huls AG
Peselev Elli
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