Trichloroisocyanuric acid and NaNO2 mediated nitration of indoles under acid-free and Vilsmeier–Haack conditions: synthesis and kinetic study

Abstract

This study deals with the synthetic and kinetic aspects of trichloroisocyanuric acid (TCCA) and NaNO2 mediated nitration of indoles in aqueous acetonitrile media under acid-free and Vilsmeier–Haack conditions (using N,N′-dimethyl amides) conditions. Nitration of indoles revealed second order kinetics, with a first order dependence on [indole] and [nitrating agent] ([TCCA]/[NaNO2], [(TCCA–DMF)]/[NaNO2] or [(TCCA–DMA)]/[NaNO2], in which [NaNO2] far excess over other reagents). Reactions followed overall second order kinetics with first order in [reagent] and [indole] under the experimental conditions. Isokinetic temperature (β) values were obtained from Leffler’s equation for different kinetic protocols (β = 303 K (TCCA–NaNO2); 303 K (TCCA–DMF)/NaNO2; and 244 K (TCCA–DMA)/NaNO2). These values are the experimental temperature range (303–323 K) indicating that the entropy factors are probably more important in controlling the reaction.