PREPARATION OF PHENYLALANINE PRECURSOR

PURPOSE:To obtain the titled compound in high yield, by reacting bisulfite addition salt of phenylacetaldehyde with prussiate ion or carbonate ion in the presence of a specific amount of ammonium ion or free ammonia. CONSTITUTION:In reacting bisulfite addition salt of phenylacetaldehyde with >=equimolar amount of prussiate ion (about 1.1mol based on 1mol bisulfite addition salt, e.g., hydrogen cyanide, etc.) or carbonate ion (about 1.1-3mol, e.g., carbonic acid gas, etc.) in an aqueous medium, >=2mol (preferably 3-7mol) ammonium ion (e.g., ammonia, ammonium carbonate, etc.) based on the carbonate ion is present, to give a phenylalanine precursor substance containing 5-benzylhydantoin as a main component. EFFECT:Easily handleable and inexpensive raw materials are used. USE:An intermediate for artificial sweeter, an intermediate for essential amino acids, etc.