Some studies of the reactions of carbon nucleophiles with aromatic nitro compounds

Abstract

Some reactions of aromatic nitro-compounds with carbon nucleophiles have been investigated. The techniques used include NMR spectroscopy, UV-visible spectroscopy and stopped-flow spectrophotometry. The initial rapid reactions of carbanions derived from ring-substituted phenylacetonitriles with 1,3,5-trinitrobenzene yield σ-adducts. Carbanions were generated from the phenylacetonitriles by reaction with sodium methoxide in methanol. Values of the equilibrium constants for the deprotonation reaction were determined spectrophotometrically. Rate constants for the σ-adduct forming reactions were measured in methanol using the stopped-flow method. With increasing carbanion reactivity rate constants for the C-C bond forming reaction increase to a limit of circa 10(^9) dm(^3) mol(^-1) s(^-1) close to the diffusion limit. Data were also obtained for reaction of the carbanions with 4-nitrobenzofuroxan and with 4-nitrobenzofurazan.An interesting slower reaction was observed in the reaction of carbanions with 1,3,5- TNB, 4-nitrobenzofuroxan and 4-nitrobenzofurazan. This yields coloured products and the nature of the process has been investigated. Attempts have been made to isolate the σ-adducts formed from carbanions. The adduct formed from 1,3,5-trinitrobenzene and phenylacetonitrile in the presence of triethylamine has been produced in crystalline form. NMR measurements in situ have indicated the formation of adducts from 4-nitrobenzofuroxan and from 4-nitrobenzofiirazan with deuterated nitromethane in the presence of triethylamine.