Substitution reactions of phenylated aza-heterocycles. Part 1. Nitration of 2,5-diphenyl-1,3,4-oxadiazole: a product study using high performance liquid chromatography

Abstract

Contrary to a previous literature report, nitration of 2,5-diphenyl-1,3,4-oxadiazole (1) under various conditions gives a mixture of all six possible 2,5-bisnitrophenyl derivatives, which may be analysed quantitatively using high performance liquid chromatography. Nitration using nitric acid alone gives mainly the three isomers with p-nitrophenyl groups, i.e.(7), (9), and (10), whereas mixed acids and nitronium tetrafluoroborate give mainly meta-nitration products, i.e.(6), (8), and (9). Nitration of the three 2-(nitrophenyl)-5-phenyl-1,3,4-oxadiazoles [i.e. the second stage of the nitration of (1)] also shows considerable variation of product ratio according to the conditions.