Effect of ortho-Substituents on Methanesulfonic Acid Derivative of Substituted Aniline

Abstract

Formation and hydrolysis rates for methanesulfonic acid derivatives (MSD) of anilines including o-, m-, and p-carboxyaniline and various ortho-substituted anilines were studies as compared with those of the other substituted anilines. For o-, m-, and p-carboxyaniline, a practical pK_a was discussed on the relationship between logarithm of formation or hydrolysis rate constant and pK_a of the corresponding anilinium ion. Formation rates for the reaction of intramolecular H-bonding aniline with hydroxymethanesulfonate were about half to those for the other substituted anilines, which supported the assumption that the reactive H in NH₂ group became half owing to the intramolecular H-bonding. In the cases of anilines substituted by negatively charged group, formation and hydrolysis rates were fairly correlated to Hammett σ value of negative group and both the rates were slower than those of the other anilines. Hammett σ values of NHCH₂SO₃-group were determined and the values of σ_m and σ_p were -0.10 and -0.57 respectively. From these observations the structure of intermediate of the reversible MSD reaction was proposed.