KINETIC-STUDY ON THE SYNTHESIS OF SOME BENZO[G]QUINOXALIN-2(1H)ONE DERIVATIVES

Some novel 3-substituted benzoquinoxalinones [R = H, CH3, C6H5, (CH2)( 2)COOH] were synthesized by the Hinsberg reaction between 2,3-diaminon aphthalene and several alpha-dicarbonyl compounds. The course of the r eactions was followed by the second uv/visible Derivative Spectroscopy Method at different pH values (-0.89 to 9.0) and also in organic solv ents at 25 degrees. The compound non-substituted at C-3 was the only o ne that could be obtained in every media in good yields (80%), having pseudo first-order anelation rate constants of relative high values (1 x 10(-1) - 1 x 10(-2) min(-1)). On the other hand, only methanol coul d be used as the organic solvent for the synthesis of all of the other compounds; aqueous media always provided better results. In the 3-met hyl derivative, as well as in the 3-phenyl derivative the change of th e reaction pH medium modified the stoichiometry of the anelation, turn ing a non-quantitative reaction into a quantitative one. This is expla ined by a change in the mechanism of the reaction on going to lower hy drogen concentrations, a fact that was supported by complementary quan titative hptlc experiments. In general, pseudo first-order rate consta nts for the anelation were one or two logarithmic units lower than tho se of the non-substituted compound (RC-3 = H), but yields were above 6 0% in every case. A reaction scheme is presented which includes a prob able mechanism.