Temperature-dependent acid dissociation constants (K/sub a/,. delta. H/sub a/,. delta. S/sub a/) for a series of nitrogen-substituted hydroxamic acids in aqueous solution

摘要: The acid dissociation constants (K/sub a/) of a series eight substituted N-phenylacetohydroxamic acids, CH/sub 3/C(O)N(OH)C/sub 6/H/sub 4/X (X = H,4-CH/sub 3/, 4-Cl, 4-I, 3-I, 3-CN, 4-CN, 4-C(O)CH/sub 3/), have been determined in aqueous solution (I 2.0) for range temperatures. pK/sub a/ data at 25 /sup 0/C exhibit small variation with the substituent X direction expected according to their Hammett (p approx. 0.1). These variations values are due compensating trends ..delta..H/sub and ..delta..S/sub a/, which show significant substituent. results discussed terms substituent's influence on hydroxamate anion-slvent interactions relative phenyl group attached C or N end moiety.