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-diaminonaphthalene and several alpha-dicarbonyl compounds. The course of the reactions was followed by the second uv/visible Derivative Spectroscopy Method at different pH values (-0.89 to 9.0) and also in organic solvents at 25 degrees. The compound non-substituted at C-3 was the only one 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 could be used as the organic solvent for the synthesis of all of the other compounds; aqueous media always provided better results. In the 3-methyl derivative, as well as in the 3-phenyl derivative the change of the reaction pH medium modified the stoichiometry of the anelation, turning a non-quantitative reaction into a quantitative one. This is explained by a change in the mechanism of the reaction on going to lower hydrogen concentrations, a fact that was supported by complementary quantitative hptlc experiments. In general, pseudo first-order rate constants for the anelation were one or two logarithmic units lower than those of the non-substituted compound (RC-3 = H), but yields were above 60% in every case. A reaction scheme is presented which includes a probable mechanism.