The invention discloses a preparation method of N-acyl acidic
amino acid or a salt thereof. According to the preparation method, fatty
acyl chloride and an
amino acid are subjected to an amidation reaction under an alkaline condition. The preparation method is characterized in that in the amidation reaction, water is used as a
solvent, an acidic
amino acid or a salt thereof is used as a main
raw material and a small amount of a neutral amino acid or a salt thereof is used as an auxiliary
raw material. The preparation method comprises the following steps: under a stirring condition, dropping the fatty
acyl chloride into the
aqueous solution of the acidic amino acid or the salt thereof; adding an alkali to adjust the pH value of the reaction solution; after a certain amount of fatty
acyl chloride is dropped, adding the
aqueous solution of the neutral amino acid or the salt thereof, continue to drop the fatty acyl
chloride until the dropping is finished and stirring to maintain the reaction. According to the preparation method, the mixed amino acid and the fatty acyl
chloride react under a water-phase
system, so that the conversion rates of the mixed amino acid and the fatty acyl
chloride can be remarkably increased and the amount of residual amino acids is greatly reduced. The product can be directly used as a surfactant after being treated simply, and thus the cost is greatly reduced.