A kinetic study of the reduction of toluidine blue with thiourea in acidic solution

✍ Scribed by S. B. Jonnalagadda; D. Tshabalala

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 405 KB
• Volume: 24
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550241110

✦ Synopsis

Abstract

A detailed kinetic study of the reaction of toluidine blue (tolonium chloride) (TB^+^ Cl^−^) with thiourea (TU) in aqueous hydrochloric acid solution is reported. The reaction was first order with respect to toluidine blue and the reductant and second order with respect to [H^+^]. Thiourea had a 2:1 stoichiometric ratio with TB^+^. Toluidine blue was reduced to a colorless base in two one‐electron reduction steps and TU was oxidized to thioformamidinium ion, which dimerized rapidly to give stable dithioformamidinium ion. The energy parameters obtained for TB^+^‐TU reaction were mean energy of activation (Ea′) = 26.7 ± 2.4 kJ M^−1^; enthalpy of activation (Δ__H__^#^) = 24.2 kJ M^−1^; frequency factor (A) = 1.04 × 10^4^ M^−3^ s^−1^; and entropy of activation (Δ__S__^#^) = −176.35 J M^−1^ s^−1^. © John Wiley & Sons, Inc.