Nitration of the tetramethylbenzenes in acetic anhydride. Formation and rearomatization of adducts

Abstract

Nitration of the tetramethylbenzenes in acetic anhydride at temperatures below –50 °C gives the l-acetoxy-4-nitro and 5-acetoxy-2-nitro adducts from the 1,2,3,4 isomer, the 5-acetoxy-2-nitro adduct from the 1,2,3,5 isomer, and the l-acetoxy-4-nitro adduct from the 1,2,4,5 isomer as well as the expected nitro derivatives. Corresponding nitritonitro adducts are also formed as well as side-chain (benzylic) derivatives: nitrates and phenylnitromethanes. Rearomatization of the tertiary acetate adducts leads to aryl acetates, benzylic derivatives, or nitroarenes, depending upon the acidity of the solvent. In the benzylic derivatives the methyl group substituted is that ipso to the acetate in the precursor adduct, that para to the most activated ipso position of the arene.