Nitro derivatives of the thiophene series. 4. Nitration of thiophene derivatives with metal nitrates in acetic anhydride

Abstract

The nitration of 2-formylthiophene, 2-acetothienone, and unsaturated ketones of the thiophene series with copper and aluminum nitrates in acetic anhydride at various temperatures was studied. At low temperatures 2-acetothienone gives a mixture of 4- and 5-nitro isomers, while 2-formylthipphene gives only a 5-nitro-substituted compound in the diacetate form; α,β-unsaturated ketones are not nitrated under these conditions. When the reaction is carried out at 70–90 °C, one can obtain mixtures of nitro ketones in the case of unsaturated ketones; 2-formylthiophene is oxidized to thiophene-2-carboxylic acid, while 2-acetothienone gives a substance, the structure of which could not be established. The reaction of copper and aluminum nitrates with acetic anhydride was investigated by means of thermal and x-ray diffraction analysis. It is shown that the reaction is accompanied by the formation of free nitric acid, and the nitrating agent in these mixtures is consequently the nitronium cation.