Kinetic study on the synthesis of some benzo[g]quinoxalin‐2(1H)‐one derivatives

Abstract

AbstractSome novel 3‐substituted benzoquinoxalinones [R = H, CH3, C6H5, (CH2)2COOH] were synthesized by the Hinsberg reaction between 2,3‐diaminonaphthalene and several α‐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°. 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 × 10−1 — 1 × 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.