GB723397A - Production of hydantoin and of glycine - Google Patents

Abstract

A process for making hydantoin comprises introducing one molecular proportion of formaldehyde into contact with an aqueous solution containing an ammonium carbonate and an alkali metal cyanide in proportions sufficient to provide the chemical equivalent of at least two mols. of ammonia, and at least 1.5 mols. of carbonate and at least one mol. of the alkali metal p cyanide, maintained at a temperature of from -10 DEG to 30 DEG C., either by slowly adding the formaldehyde in the form of an aqueous solution at a rate such that not more than one mol. of the formaldehyde is released into contact with the dissolved salts in the solution over a period of 4 hours or more or by dissolving a proportionate amount of paraformaldehyde in the solution, then heating the solution at a temperature of from 50 DEG to 120 DEG C. to complete the reaction and form hydantoin. Glycine is prepared by boiling the aqueous reaction liquid to distil ammonia and carbon dioxide, mixing the residual aqueous liquid with an alkali metal hydroxide in amount corresponding to at least two mols. of the alkali metal hydroxide per mol. of the formaldehyde starting material, heating the alkaline solution at a temperature between 130 DEG and 250 DEG C. under pressure to hydrolyse the hydantoin and recovering glycine from the alkaline hydrolysis liquid. Starting materials mentioned include sodium or potassium cyanide and ammonium carbonate or bicarbonate. The alkaline solutions containing hydantoin and glycine are treated with cation exchange resins in hydrogen form to remove alkali metal ions before separating the desired products. Insoluble sulphonated vinyl aromatic resins and sulphonated phenol-formaldehyde resins are mentioned. In examples: hydantoin is obtained by dissolving paraformaldehyde in an aqueous solution containing sodium cyanide and ammonium bicarbonate, boiling the solution, treating it with decolourizing charcoal and a sulphonated vinyl aromatic resin in hydrogen form and concentrating and cooling the residual solution (1); reaction liquor from (1) is heated in an autoclave with sodium hydroxide and the solution is decolourized, boiled, cooled, treated with the ion exchange resin used in (1); concentrated and treated with methyl alcohol to obtain glycine (2); and formaldehyde is gradually added to an aqueous solution of ammonium carbonate and sodium cyanide, the mixture is heated under pressure, ammonia and carbon dioxide are boiled off, aqueous caustic soda is added and the solution is pumped through a heated tube to effect hydrolysis of the hydantoin. The hydrolysed solution is treated with the ion exchange resin used in (1) and concentrated and glycine is precipitated by the addition of methyl alcohol. Specifications 687,486 and 693,522 are referred to. Reference has been directed by the Comptroller to Specifications 687,486 and 693,522.