Solvent Hydrogen Bonding and Structural Effects on the Reaction of 2-Halo-5-nitropyridines with Parasubstituted Anilines in Dimethylsulfoxide/Acetonitrile Mixtures

Substitution reactions of some parasubstituted anilines with 2-chloro-5-nitropyridine and 2-bromo-5-nitropyridine were carried out conductometrically in dimethylsulfoxide/acetonitrile mixtures. The correlation of second order rate constants with Hammett's substituent constants yields a fairly linear straight line with a negative slope. The correlation of rate data with Kamlet-Taft's solvatochromic parameters is excellent (100R(2) = 97%) in both the substrates. The solvation model proposed is well supported by the solvatochromism exhibited by aniline in the solvent mixture under investigation. The molar extinction coefficient (epsilon(max)) of aniline varies appreciably up to similar to 25% with the change in composition of the mixture. The multivariate correlation analysis of epsilon(max) (with alpha, beta, pi*) suggests that the solvation around NH2 moiety of aniline through hydrogen bond donor (HBD) property is found to be dominant in the solvation process and consequently in altering the rate. The observation is that the dominance of HBD property in solvation is further confirmed by the cyclic voltammetric oxidation of aniline in the solvent mixture. (C) 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 409-417, 2011