Theoretical Study on Thermodynamic and Spectroscopic Properties of Electro-Oxidation of p-Aminothiophenol on Gold Electrode Surfaces

Abstract

The electro-oxidation of p-aminothiophenol (PATP) on gold electrodes has been investigated by means of density functional theory. A combination of thermodynamic calculations and surface Raman and infrared (IR) spectral simulations has allowed us to reveal the electro-oxidation mechanism and reaction products of PATP on gold electrodes in acidic, neutral, and basic solutions. PATP can be first oxidized to the radical cation PATP(NH2•+) or the neutral radical PATP(NH•) depending on the pH of aqueous solutions, and this is the rate-determining step. The radical cation or neutral radical can then transform to the dimerized products through a radical coupling reaction. In the acidic medium, the radical cation reacts with its resonance hybrid through a N–C4 coupling to form 4′-mercapto-N-phenyl-1,4-quinone diimine (D1), which can further undergo hydrolysis to yield 4′-mercapto-N-phenyl-1,4-quinone monoimine (D2). In the neutral medium, the neutral radical reacts with its resonance hybrid through the N–C2(6) cou...