Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1997-05-13
1998-12-08
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C07C31500
Patent
active
058472070
DESCRIPTION:
BRIEF SUMMARY
This application is based on German Patent Application 4428608.2 filed Aug. 12, 1994 and PCT/EP98/03068 filed Aug. 2, 1995, the contents of which are incorporated hereinto by reference.
The invention is relative to a process for producing 2-hydroxy-4-methylthiobutyric acid (MHA) according to the generic part of claim 1 as well as to the use of the MHA produced according to this process.
In particular, the invention is relative to an improved, novel process for simultaneously obtaining MHA and crystalline ammonium sulfate or ammonium bisulfate in high yield and purity while avoiding a waste water which requires treatment and optionally contains salt.
2-hydroxy-4-methylthiobutyric acid (MHA) is the hydroxy analogue of the essential amino acid methionine in racemic form and is, like the latter, an important additive in animal nutrition. In the raising of poultry MHA exhibits similar growth-stimulating properties like the amino acid known for this. However, the additive is also becoming increasingly interesting in other areas of animal nutrition.
BACKGROUND OF THE INVENTION
MHA is usually used in the form of aqueous concentrates which also contain a certain amount of oligomers, primarily the di- and trimeric linear ester acids, in addition to the monomer. The content of these oligomers is a function of the production conditions and the concentration selected. However, on account of their low nutritive efficiency and the unfavorable influence on the flow properties due to elevation of viscosity it is desirable to keep their percentage as low as possible. Commercial formulations have, at a total concentration of 8-90% by weight, less than 20% by weight, preferably less than 17% by weight in the sum of oligomers, corresponding to a monomer/oligomer ratio of .about.4:1 to 5:1.
The use of the calcium salt and of the mixed calcium ammonium salt of MHA as feedstuff additive is also known. However, the production of these salts is associated with higher production costs. Moreover, they are harder to mix in as powdery solids into the feedstuff formulation than the aqueous concentrates of the free acid with a low amount of oligomers, which concentrates can be readily sprayed.
The synthesis path to MHA consists of 3 reactions.
The general process for the production of MHA starts with 3-methylthiopropionaldehyde, also designated as methylmercaptopropionaldehyde or MMP, which is reacted with hydrogen cyanide to 2-hydroxy-4-methylthiobutryonitrile, also designated as MMP-cyanohydrin or MMP-CH (equation I). ##STR1##
The MMP-cyanohydrin produced is subsequently customarily hydrolyzed with strong mineral acids via the intermediate stage of 2-hydroxy-4-methylthiobutyramide, also designated as MHA amide, (equation II) ##STR2## to the methionine hydroxy analog (MHA) (equation III). ##STR3## This hydrolysis can be carried out in one or in two stages.
A two-stage procedure starting with MMP-cyanohydrin is described in U.S. Pat. No. 2,745,745; 2,938,053 and 3,170,000. In them the cyanohydrin is first reacted to the MHA amide at relatively low temperatures with concentrated mineral acid, e.g. with 50-85% sulfuric acid, whereupon the hydrolysis to MHA is continued after the addition of water at elevated temperature. The calcium- or calcium ammonium salt of MHA and calcium sulfate as coupling product are obtained therefrom by treating the saponification mixture with calcium hydroxide or--carbonate. In order to reduce the compulsory accumulation of worthless byproducts the two patents cited first recommend that the hydrolysis agent sulfuric acid be added in a hypostoichiometric ratio to the MMP-cyanohydrin, e.g. 0.55-0.8:1. British patent 722,024, which describes the same type of formation of the MHA salts starting with MHA amide, implies the two-stage procedure.
The processes published in European patents 0,142,488 (with sulfuric acid) and 0,143,100 (with mineral acid), which have as subject matter the obtention of MHA in liquid form, that is, highly concentrated aqueous solutions, use the two-stage hydrolysis. The latter is obtaine
REFERENCES:
patent: 5386056 (1995-01-01), Matsuoka
Hafner Volker
Suchsland Helmut
Degussa - Aktiengesellschaft
Killos Paul J.
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