Differential kinetic determination of mixtures of aniline and its derivatives using N,N-dimethyl-p-phenylenediamine.

Abstract

The oxidative coupling reaction between the quinonediimine (QDI) of N, N-dimethyl-p-phenylenediamine (DMPD) and aromatic amines was utilized for the simultaneous determination of binary mixtures of aniline and its derivatives by the differential reaction rate method. A mixture of oxidant and DMPD was used instead of QDI because QDI was unstable. The effects of pH and the oxidant (K3Fe (CN)6, K2Cr2O7 and their mixture) on the stability of the first oxidation product of DMPD, semiquinone (SQ), and on the equilibrium among DMPD, SQ and QDI, were investigated. The second-order rate constants of two amines reacting with QDI and the overall pseudo first-order rate constant of a mixture were determined from the slope of the straight line (the concentration of SQ vs. time) and by simplified complementary tristimulus colorimetry. Mixtures of amines down to 1.0×10-4M were determined. Most relative errors were in the range of 0 to 14%. Among the compounds examined for interference, phenols and carbonyl compounds showed serious effects.