Process for the preparation of alpha-amino acids by hydrolysis of hydantoins at elevated pressure and elevated temperature

A process for the preparation of an α-amino acid by a reaction comprising hydrolyzing a hydantoin of the formula

• in which
• R1, R2:
• can be identical or different, and represent hydrogen, alkyl having from 1 to 6 carbon atoms, straight-chain or branched chain;
• or alkylene radicals having from 1 to 6 carbon atoms which are closed to form a ring when R1 and R2 taken together are alkylene or, when R1 or R2 represents alkylene, are bonded to methylthio, mercapto, hydroxyl, methoxy, amino groups or halogen atoms, or
• R1 and R2:
• can also be a phenyl group which is optionally substituted by methyl, hydroxyl groups or halogen atoms,
• in the presence of water, ammonia as starting materials and at least one metallic oxide as catalyst, selected from the group consisting of TiO2, TiO2/Al2O3, Nb2O5/Al2O3, ZnO and ZrO2, in a saponification zone under conditions in which all starting materials are completely dissolved in the water and only one further phase is present in the reactor in addition to the solid phase of the metallic oxide.