The Investigation of Amino Acid Reactions by Methods of Non-aqueous Titrimetry

The present paper is intended as a contribution to the specific chemistry of the naturally occurring hydroxyamino acids. Certain established differences in the chemistry of the acyl derivatives of amino and hydroxy groups have so far not been utilized in the study of hydroxyamino acids, and in particular no simple method for the preparation of their 0-acetyl derivatives has been developed. The long known catalytic effect of strong acids in the reaction of hydroxy groups with acetic anhydride has been the object of a quantitative study in aceteous medium (Conant and Bramann (4)). On the other hand, it also has long been recognized (Pinnow (11)) that the acetylation of primary amines by acetic anhydride is greatly inhibited when they are present as salts of strong acids.’ The preceding paper (Kolb and Toennies (6)) contains evidence indicating that the acetylation of amino acids by acetic anhydride in aceteous medium is greatly repressed by salt formation with perchloric acid, and an earlier study (Toennies and Elliott (20)) dealt with the accelerating effect in the same medium of perchloric acid on the acetylation of water by acetic anhydride. The present work shows that the catalyzed reaction of the -OH group of amino acids is very similar to that of water. The analytical determination of that reaction and its differentiation from the acetylation of amino groups is accomplished as follows: If an aceteous solution of an