Effect of benzoic acid on the cathodic reduction of aromatic nitro compounds in N,N-dimethylformamide

Abstract

The effect of benzoic acid on the polarographic reduction of two series of aromatic nitro compounds in N,N-dimethylformamide has been investigated. The first reaction series was p-XC 6H 4NO 2 compounds, whereas the second one comprised mononitroarenes. In the presence of the acid a new cathodic wave (pre-wave) appeared at more positive potentials than the original (orig.) wave of the reactant. The pre-wave was associated with the reduction of a hydrogen bonded adduct of 1:1 type formed between the nitro-group and the acid in the double layer of the electrode. Linear correlations have been found between Δ E 1 2 and p K BH values for both reaction series (Δ E 1 2 = E pre-wave 1 2 − E orig.wave 1 2 and p K BH denotes the negative logarithm of the acidity constant of the protonated nitro compound). The slopes of regression lines are considered in terms of the double layer effects on the basicity of the NO 2 group in the molecules under study.