FIELD: organic chemistry, chemical technology, amino acids. SUBSTANCE: invention relates to method of synthesis of long-chain N-acylated acid amino acid (I) involving step (washing out step) of impurities removal by separation of mixture of long-chain N-acylated acid amino acid. Amino acid is prepared by fulfillment of the following steps being this amino acid comprises inorganic salts as impurity and medium consisting mainly of water and tertiary butanol for an aqueous layer and tertiary butanol for an aqueous layer and an organic layer containing long-chain N-acylated acid amino acid at temperature from 35 to 80 C: 1) step (acylation step) of condensation of acid amino acid and long-chain saturated acid halogen anhydride in mixed solvent containing mainly water and tertiary butanol in the presence of alkali; 2) step (separation step by acid precipitation) by pH value brought about to 1-6 with mineral acid for separation of mixture for an organic layer and an aqueous layer. This procedure results to preparing an organic layer containing long-chain N-acylated acid amino acid with regard to three variants of long-chain N-acylated amino acids or their salts, to two species of liquid and solid cosmetic composition and two species of detergent composition. The proposed method ensures to simplify method of synthesis of (I) and to prepare (I) without odor practically in addition to liquid detergent or cosmetic composition containing (I) being without its turbidity and precipitate formation for a long storage time and especially at low temperatures. EFFECT: improved method of synthesis. 19 cl, 7 tbl
