GC-Mass Spectrokinetics Study of Probable Mechanism of the Oxidation of Diethylthiourea with Toluidine Blue

Abstract

Thecurrent study describes the interactive role of diethylthiourea on the bleaching of toluidine blue (tolonium chloride) (TB) in acidic and basic media using the GC Mass Chromatography and Spectrophotometric technique. GC-Mass Spectrophotometric analysis was carried out to verify the decoloration of dye whether the bleaching of dye owed to leuco dye formation or degradation may also occur in the reaction mixture. The dye redox reaction process followed first order kinetics with respect to TB, DETU showed first order mechanism, first order kinetics with respect to H. Enhanced decoloration in the presence of DETU proved that reductant‘s role is pivotal in the redox reaction. Slow decoloration in basic medium with ions was seen compared to acidic media, suggesting that pH of the medium is significant in the oxidation of DETU. The bleaching reaction of dye was investigated at different temperatures. At pH of 1.0 and 25C, the order of reaction is found to be second having rate constant value of 15.81 mol.L s,and rate law is suggested to be -d/dt [TBH ] = k2 [TB + H][DETU].Different reaction energy parameters were evaluated for a TB-DETU reaction, including the energy of activation (Ea = 60.786 kJmol -1 (basic medium), 1.669kJmol (acidic medium)), enthalpy of activation (∆H ≠ = -58.267 kJ mol -1 (basic medium), -12.6kJ mol -1 (acidic medium)), entropy of activation (∆S = -131.525JmolK(basic medium),-243 JmolK(acidic medium)),and free energy of activation (∆G = 98.119kJmol (basic medium) and -86.55kJmol (acidic medium). A mechanism of interaction of involved ions in dye bleaching and a mechanism of oxidation based on the above findings is proposed.