Amine functionalization of N,N,N′,N′-tetramethyl-p-phenylenediamine for the electrosynthesis of a wide range of p-phenylenediamines in green conditions

Abstract

The voltammogram features of TMPD²⁺/TMPD, N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), reflect the intensive instability of TMPD²⁺ in aqueous solutions. The instability of TMPD²⁺ strongly restricts its application in electrochemical syntheses. The striking feature of this paper is the stabilization of this redox-active species via amine functionalization. The procedure started with the chemical reaction of TMPD with sodium nitrite to produce N-(2-nitro-4-(dimethylamino)phenyl)-N-methylnitramide (NDPM). The nitro functional group of NDPM was reduced electrochemically to the corresponding amine derivative, N-(2-amino-4-(dimethylamino)phenyl)-N-methylnitramide (ADPM). Unlike TMPD²⁺/TMPD, the voltammetric results of ADPM presented a reversible redox process at low redox potentials. The phenomenon introduces ADPM as an effective compound for the electrochemical synthesis of p-phenylenediamine derivatives in green conditions. To examine the hypothesis, we have developed a paired electrochemical synthesis method via the reduction of NDPM at the surface of the cathode followed by oxidation at the anode surface in the presence of arylsulfinic acids as typical nucleophiles. The electrochemical synthesis was successfully performed under green conditions in the absence of redox mediators.