Substituent effects in the electrophilic substitution of deactivated systems. Part I. The nitration of 4-alkylphenyltrimethylammonium ions

Abstract

Second-order rate coefficients have been measured at several temperatures for the nitration, in 98 and 82 % aqueous sulphuric acid, of the series p-RC₆H₄·NMe₃⁺ClO₄^– where R = Me, Et, Prⁱ, or Bu^t. The alkyl groups greatly enhance reactivity. Direct experimental comparison shows that p-tolyltrimethylammonium perchlorate is nitrated more readily than phenyltrimethylammonium perchlorate, in the meta-position, by a factor of 3500 in 98 % sulphuric acid and 2600 in 82 % sulphuric acid. Comparison of relative reactivities of the 4-alkylphenyltrimethylammonium ions with those reported for chlorination, bromination, and nitration of alkyl benzenes indicates that even in this highly electron-demanding situation alkyl groups influence nitration by electron release in the inductive order.