GB614916A - Improvements in or relating to the preparation of unsymmetrically substituted guanidines and acid salts thereof - Google Patents

Abstract

Salts of substituted guanidines are prepared by reacting an aqueous solution of cyanamide with a mixture of a primary or secondary amine having a dissociation constant of at least 1 X 10-6 together with an acid salt of the amine at a temperature of from 80 DEG to 170 DEG C., there being sufficient of the free amine present to raise the pH of the reaction mixture to 8 or higher. The free guanidines may be obtained by neutralizing their salts with an alkaline substance. Primary amines yield monosubstituted guanidine compounds whilst secondary amines yield unsymmetrically di-substituted compounds. At the higher temperatures the reaction is carried out under pressure. Preferably only a low concentration of cyanamide is maintained present during reaction; thus, an aqueous solution of cyanamide may be added to the reaction mixture progressively so that there is not more than about 0.25 mole. of unreacted cyanamide present per mole. of unreacted amine calculated as free amine and amine salt. Generally, the molar quantity of free amine present does not exceed that of the amine salt. The process may be made continuous. In examples: (1) an aqueous cyanamide solution is progressively run into an aqueous sulphuric acid solution containing excess methylamine (pH 10) at 170 DEG C. in an autoclave to yield methyl guanidine sulphate; (2) a series of experiments are described illustrating the preparation of mono-methyl guanidine nitrate, mono-n-butyl guanidine nitrate and N,N-pentamethylene guanidine nitrate from methylamine-, butylamine- and piperidine-nitrate respectively in the absence and presence of excess of the amine at pH values from 2 upwards and the yields are compared; (3) di-n-butyl guanidine nitrate is prepared as in (1) from di-butylamine and its nitrate; (4) a series of experiments are carried out as in (1) using a mixture of methylamine and methyl ammonium methyl carbamate prepared by treating liquid methylamine with solid carbon dioxide; (5) butyl guanidine hydrochloride is prepared similarly, from butylamine and its salt, converted into the base and then, by means of carbon dioxide, into the bicarbonate; (6) octadecyl guanidine hydrochloride is prepared likewise from octadecylamine and its salt dissolved in aqueous butanol, and converted into the carbonate by means of sodium carbonate. Other amines specified are dimethylamine, ethylamine, isoamylamine, benzylamine, phenylethylamine, N - ethyl - benzylamine, octylamine, laurylamine, stearylamine, morpholine, cyclohexylamine and monoethanolamine; the amines may be used in the form of their sulphates, nitrates, hydrochlorides, carbonates, carbamates, acetates, propionates, succinates and phthalates. The Specification as open to inspection under Sect. 91 includes the use of any primary or secondary amine and is not limited as regards conditions of temperature and pH. This subject-matter does not appear in the Specification as accepted.