INFLUENCE OF SUBSTITUTES ON THE RATE OF REACTION OF SUBSTITUTED ANILINES WITH A BENZOIC ACID, CATALYZED BY POLYBUTOXYTITANATES

Abstract

The catalytic production of benzanilide by the interaction of benzoic acid with aniline is an important model process recently intensively developed in the field of the concept of «green chemistry», direct catalytic amidation, and its study is an urgent scientific and practical task.  To solve this problem, the effect of substituents in the aniline core on the catalysis by polybut-oxytitanates on acylation of substituted  anilines  by benzoic  acid  was  studied. The rate constants of this the second-order reaction (the first with respect to substituted aniline and benzoic acid; boiling ortho-xylene, 145 °С, nitrogen flow)  are well correlated according to the Hammett equation with three straight lines for individual groups of substituents with ρ = –0.86 (electron donors), 1.12 (weak electron acceptors),  –2.83 (strong  electron  acceptors). To explain this dependence, a variant of the catalytic amidation mechanism is proposed, which takes into account the formation of titanium butoxybenzoates in the first minutes of the reaction — a true  amidation  catalyst;  coordination (polarization of the carbonyl bond in the interaction with the catalyst titanium atom) and acid (polarization of the carbonyl bond in the interaction with the complex of the formed substitu- ted benzanilide with the titanium butoxyben-zoates)  catalysis   routes. Inhibition of the catalytic reaction is associated with the presence in the mass of water, relative excess of  benzoic acid and a possible amide–imide tautomerism of substituted benzanilides, accompanied by the interaction of the imide form of the latter with titanium  butoxybenzoates, which does not lead to the route of acid catalysis. The rate constants for catalytic acylation of substituted anilines, containing  electron-donating substituents, with benzoic acid in the  air are correlated according to the Hammett equation by a straight line segment with ρ = 0.99, which is associated with the predominant influence  of  the  oxidation  processes  of  the  corresponding   amines. Catalytic acylation under comparable conditions of substituted anilines, containing electron-withdrawing substituents, oxidation processes due to atmospheric  oxygen  have  little  effect  on.