GB719144A - The preparation of methionine from ª‡-amino-ª†-methylthiobutyronitrile - Google Patents

Abstract

In the manufacture of methionine by hydrolysis of crude methionine nitrile containing by-products which yield tarry matter on hydrolysis, a solution of the crude nitrile in an organic solvent or mixture of organic solvents is reacted with phosphoric acid or sulphuric acid so as to precipitate the corresponding phosphate or sulphate which is removed and hydrolysed, the solvent or solvents being such that the nitrile salt is substantially insoluble and the by-products substantially soluble therein. Preferred solvents are the low molecular weight aliphatic alcohols such as ethanol, iso-propanol and n-butanol; methanol alone may be used to treat the sulphate but not the phosphate-in the latter case, methanol in conjunction with a substantially equal volume of a solvent in which the phosphate is only sparingly soluble may be used. Acetone and monoalkyl ethers of simple glycols, e.g. b -ethoxyethanol, are also suitable. In examples: (1) concentrated sulphuric acid is added dropwise to a cooled solution of crude methionine nitrile in dry ethanol and the precipitated sulphate is filtered off and hydrolysed to methionine by refluxing with aqueous sulphuric acid; (2) phosphoric acid is added dropwise to an ethanolic solution of crude methionine nitrile and the precipitated dihydrogen phosphate is hydrolysed as in (1). Use of dioxane, methylethylketone or ethyl acetate as solvent in place of ethanol in these examples results in a tarry product being produced; a similar result obtains using a 4 : 1-ether-methanol mixture in example 2. The crude methionine nitrile may be prepared from b -methyl thiopropaldehyde by known procedures.