Reactions of aromatic nitro-compounds in alkaline media. Part XI. Structural investigations by proton magnetic resonance spectroscopy

Abstract

The interactions of a series of di- and tri-nitrobenzene derivatives with base (mostly methoxide in a mixed solvent of equimolar amounts of methanol and dimethyl sulphoxide) have been investigated by proton magnetic resonance spectroscopy. Three types of interaction are recognised: (a) addition of base to a nuclear position carrying hydrogen (e.g., 1,3,5-trinitrobenzene, NN-dimethylpicramide), (b) addition of base to a nuclear position carrying a substituent, usually a methoxyl group (e.g., methyl picrate, 2,4-dinitroanisole), and (c)(primary or secondary amines) loss of a proton from an amino-group (e.g., 2,4- and 2,6-dinitroaniline, 2,4-dinitrodiphenylamine). In picramide proton loss and methoxide addition of type (a) compete and their relative proportions can be changed by varying the base and solvent used. In several cases two equivalents of methoxide can react with one aromatic molecule: e.g., NN-dimethylpicramide can add two methoxide ions in equivalent positions, whereas one molecule of N-methylpicramide can lose an amino-proton and add a methoxide ion to the aromatic ring.

Addition of type (a) tends to be more rapid than type (b), but the latter process results in the thermodynamically more stable product.