The 3:5-dinitrobenzoyl derivatives of the amino-acids and their use in separating the isomers of leucine and valine.

IN recent papers, Saunders [1934; 1938] has described the preparation of the 3:5-dinitrobenzoyl derivatives of certain amino-acids and has suggested their use for purposes of identification. This possibility has been confirmed by the present author; however, certain discrepancies have been observed between published data and present experience and these observations are embodied in this communication. In the first place, the reaction between 3:5-dinitrobenzoyl chloride and amino-acids has been found to be much slower thah stated by Saunders. Reaction times of the order of 30 min. have been found, compared with quoted times of 2 min. for similar quantities of material. It was also observed that some 3:5-dinitrobenzoic acid is always obtained during benzoylation, even when molecular proportions of reactants are em]qloyed, and this can be very troublesome. It is suggested by Saunders that practically no 3:5-dinitrobenzoic acid is formed during the reaction. It has also been found that the melting points ofsome of the derivatives differ considerably from those quoted by Saunders, and such differences are noted in the experimental section of the paper. Also in the cases ofvaline and leucine more than one derivative has been isolated. The melting points of the derivatives which the author has been able to prepare are quoted in Table 1. These melting points have -been consistently obtained in this laboratory and are believed to be correct.