The catalytic synthesis of benzanilide by the interaction of benzoic acid with aniline is an important model reaction of direct catalytic amidation that has been intensively developed recently in the field of the concept of «green chemistry», and its study is an urgent task.
In the framework of solving this problem the effect of the final product - benzanilide, and its substituted on catalysis by tetrabutoxytitanium and its partial hydrolysis products (polybutoxytitanates) was studied. With an increase in the concentration of the preliminary addition of benzanilide, the initial rate of catalytic interaction of benzoic acid with aniline decreases monotonically.
Benzanilide itself does not catalyze the amidation process, does not hydrolyze under reaction conditions by water, and does not undergo other changes in the reaction mass.
The kinetics of the formation of benzanylide in the presence of additives of a number of substituted benzanilides, containing electron-withdrawing substituents, showed higher values of the reaction rate constants as compared to that for the formation of benzanilide in the absence of any additives. This suggests the presence of two routes of catalysis: the coordination route (polarization of the carbonyl group of the benzoic acid due to the interaction with the atom of titanium) and acid route. The latter can be associated with the formation of complexes due to the coordination of the titanium atom of the catalyst with the carbonyl group of the substituted benzanilide, the appearance of a relatively acidic NH=group and catalysis of conjugate acid: the titanium-containing catalyst + the corresponding substituted benzanilide.
The formation of such a catalytic complex, by the example of a pair of benzanilide + tetrabutoxytitanium, was confirmed by the NMR 1H spectroscopy method.
Catalysis of aniline acylation with benzoic acid in the presence of additions meta= and para=substituted benzanilides correlates well with the Hammett equation with two straight line segments with ρ=0.478 and ρ=-0.235, with a maximum, indicating a different effect of substituted benzanilides containing electron-donating and strong electron-withdrawing substitutes on the complexation with tetrabutoxytitanium and polybutoxytitanium and the change in their catalytic activity.
The decrease in the rate of the catalytic formation of benzanilide is especially pronounced with the addition of ortho=substituted benzanilides, containing strong electron-withdrawing substituents, which at the same time have a high steric effect.
EFFECT OF SUBSTITUTED BENZANILIDES ADDITIVES ON THE SPEED OF CATALYZED BY TETRABUTOXYTIITANE AND POLYBUTOXYTIТANATE REACTION OF ANILINE WITH BENZOIC ACID