Electrochemical behaviour of 2-nitrophenylguanidines in acetonitrile

Abstract

4-Methyl-2-nitrophenylguanidine (I) is reduced in two steps (at −1.30 and −1.51 V vs. aqueous SSCE) in 0.1 M Et 4NBF 4 in acetonitrile. Both reduction steps seem to have a prekinetic character in fast cyclic voltammetry (5–100 V s −1 at a DME. The ratio of the polarographic limiting currents is approximately 1:4. The reduction proceeds in an adsorbed state in both steps. Other nitrophenylguanidines (ethylated on the guanidine residue) studied show reduction properties very similar to those of I. The products of the controlled potential electrolysis of I at −1.4 V in acetonitrile were separated by means of elution chromatography and characterized by IR and UV-vis. spectra. The products of the ring closure of I, i.e. 3-amino-7-methyl-1,2,4-benzotriazine-1,4-dioxide (II), 3-amino-7-methyl-1,2,4-benzotriazine-1-oxide (III) and 3-amino-7-methyl-1,2,4-benzotriazine (IV), were found to be the components of the reaction mixture along with the products of the eliminationn of the carbodiimide residue from I, i.e. 4-methyl-2-nitroaniline (V) and the oligomeric organomercury compound yielding melamine (X) after decomposition. The proposed mechanism of ring closure of I involves dipolar addition of the anion of I to I to form a “dimer” with an NON grouping, cleavage of the NO bond and cyclization.