A process for the preparation of a salt of an ωester of an amino dicarboxylic acid, comprising A) reacting the ammo dicarboxyic acid with a benzyl alcohol derivative of the formula
- wherein R1 is individually selected from the group consisting of hydrogen, C1 to C4 alkyl, C1 to C4 alkoxy and halogen and n is 1 or 3, in the presence of an alkanesulfonic acid catalyst with a molar ratio of at least one mole of catalyst per mole of the amino dicarboxylic acid, B) optionally in the presence of a solvent to obtain a salt thereof and optionally reacting the salt with a base to obtain the free form thereof.