A STUDY OF CYCLODEHYDRATION AND HYDROLYSIS OF ORTHO-AMINOANILIDES .6.THE KINETICS AND MECHANISM OF ISOMERIZATION AND HYDROLYSIS OF N-(2-AMINOPHENYL)PHTHALIMIDE IN SOLUTIONS OF H2SO4

The kinetics of hydrolysis of N-(2-aminophenyl)phthalimide and its iso merization to 2-(2-carboxyphenyl)-benzimidazole in 0.05 - 97% H2SO4 is studied by spectrophotometry. It is shown that the isomerization reac tion proceeding at C(H2SO4) < 55% involves a reactive complex that con sists of imide protonated at the amino group (pK(BH+) = 2.28) and a wa ter molecule (BH+ . H2O). A decrease in the reaction rate in 5 - 55% H 2SO4 is attributed to the production of the BH+ - HSO4- ionic pair. Im ide hydrolysis occurs by the two following routes: in 10 - 75% H2SO4, that pathway predominates in which the rate is proportional to concent rations of BH+ and H5O2+ ions and decreases because of producing the B H+ . H5O2+ . H2O complex, and in 80 - 97% H2SO4, the second route invo lving a monomolecular decay of BH+ ions prevails. On the basis of the dependence of the effective rate constants on die medium composition, the elementary rate constants of both reactions as well as the rate co nstant of ionization of N-(2-aminophenyl)phthalimide via amino and car bonyl groups are determined.