Corey-Suggs and Cornforth reagents and sodium nitrite triggered nitration of aromatic and heteroaromatic compounds – A synthetic and kinetic study in aqueous acetonitrile media under acid-free conditions

Abstract

Abstract In this study, Cornforth reagent (pyridinium dichromate or PDC)/ NaNO2, and Corey-Suggs reagent (pyridinium chlorochromate or PCC)/ NaNO2 were used to trigger nitration of aromatic and heteroaromatic compounds (substrates) under acid-free conditions in (2%) aqueous acetonitrile medium. Microwave (MW) assisted reactions under solvent-free conditions reduced the reaction times enormously with higher product yields. Kinetics of these reactions revealed first order in [Substrate], [PDC] (or [PCC]), under the conditions [NaNO2] ≫ [PDC] (or [PCC]). Observed kinetics together with the linearity of Kirkwood plots revealed ([(PyH)OCrO2NO2] and substrate in (PDC/NaNO2), and [(PyH)OCrO(OH) (NO2) Cl] and substrate in (PCC/NaNO2) triggered reactions, in the rate limiting step to explain nitration mechanism. Observed isokinetic temperature (β)” values, 285K (PDC/nitrite) and (269K for PCC/nitrite) were below the experimental temperature range (303 to 323K), suggesting that the entropy factors overweigh enthalpy factors in controlling the reaction.