Reactions in strongly basic media. Part 9. Correlation of the rates of methoxide-catalysed methanolysis of 1-substituted 2,4-dinitrobenzenes and 2-substituted 5-nitropyridines in methanolic dimethyl sulphoxide with an acidity function. Details of the mechanistic pathway

Abstract

The rate coefficients for the methoxide-catalysed methanolysis of a series of 1-substituted 2,4-dinitrobenzenes and 2-substituted 5-nitropyridines have been measured in methanolic DMSO at 20.0 or 21.0 °C. For the 2-substituted 5-nitropyridines and for the 1-substituted 2,4-dinitrobenzenes below ca. 55 mol% DMSO, the rates have been correlated with an acidity function of the medium. The slopes of these linear relations are discussed. The 1-substituted 2,4-dinitrobenzenes above ca. 55 mol% DMSO give rise to Meisenheimer complexes as intermediates and/or as the product of the reaction. The product of the reaction then becomes the 1,1-Meisenheimer complex of methoxide and 2,4-dinitroanisole. For the 1-fluoro substrate the formation of the latter becomes rate determining. For other 1-substituted substrates the decomposition of a 1,3-Meisenheimer complex becomes rate determining.