Electronic effects of substituents in aromatic nitration (1965)
AuthorsWright, G. J.show all
Product distributions from the nitration of toluene, o-xylene, m-xylene, hemimellitene and pseudocumene have been determined in nitric acid-acetic anhydride mixtures, nitronium tetrafluoroborate-sulpholane mixtures and in the nitric acid-sulphuric acid-nitromethane system. The Additivity Principle is applied to the toluene results to calculate product ratios for the other hydrocarbons. Comparison of calculated and experimental results shows this to be an unsatisfactory method of calculating product distributions for these reactions. The differences between calculated and experimental results are examined quantitatively in terms of modified ortho substituent constants. Mixtures of nitric acid in acetic anhydride are shown to bring about direct acetoxylation of the aromatic nucleus when activated by more than one methyl group. The acetoxylation reaction has the characteristics of an electrophilic substitution reaction with large steric requirements and high selectivity. An estimate of the Hammett rho for the reaction is made. Product distributions from the nitration of indan and tetralin in the three nitrating systems have also been determined. These results are discussed in terms of the Mills-Nixon effect. An explanation for these and the results of other investigations of indan and tetralin is presented.