Kinetic and mechanistic studies of the oxidation of poly(o-toluidine) doped with 5-sulfosalicylic acid

Protonation of poly(o-toluidine) base form (POT-EB) with 5-sulfosalicylic acid (SSA) was proved experimentally and computationally. Molecular mechanics (MM+) calculations showed that the potential energy (PE) of the optimum molecular geometric structure of SSA-doped POT is 4.703 x 10(3) kcal mol(-1) or at least three orders of magnitude higher than the PE of the molecular geometric structure of the same matrix. These calculations indicate that the optimization of this matrix is necessary for understanding the stability. Dark green coloration (lambdasimilar to800 nm) after addition of SSA into POT-EB matrix (dark blue, lambdasimilar to600 nm) revealed that the SSA was working as a protonating agent to convert POT base form (POT-EB) to salt form (SSA-doped POT). The change of the dark green color of SSA-doped POT to dark brown (lambdasimilar to500 nm) after addition of oxidant (K2CrO4) was due to the highest oxidized form of the matrix obtained (the quinoid one), which undergoes a hydrolysis reaction to produce p-hydroquinone (H2O) by a mechanism similar to Schiff-base hydrolysis. Kinetic parameters of the oxidation reaction were deduced employing a computer-aided kinetic analysis of the absorbance (A) at similar to800 nm against the hydrolysis time (t) data. The results obtained indicate that the rate controlling process may be governed by the Ginstling-Brounshetin equation for three-dimensional diffusion (D4). The proposed mechanism for the oxidation of SSA-doped POT matrix is also supported by MM+ calculations. Activation parameters for the rate of the oxidation process of acid-doped POT matrix have been computed and discussed. (C) 2003 Wiley Periodicals, Inc.