14451-43-5Relevant academic research and scientific papers
S-oxygenation of thiocarbamides I: Oxidation of phenylthiourea by chlorite in acidic media
Chigwada, Tabitha R.,Chikwana, Edward,Simoyi, Reuben H.
, p. 1081 - 1093 (2005)
The oxidation of 1-phenyl-2-thiourea (PTU) by chlorite was studied in aqueous acidic media. The reaction is extremely complex with reaction dynamics strongly influenced by the pH of reaction medium. In excess chlorite concentrations the reaction stoichiometry involves the complete desulfurization of PTU to yield a urea residue and sulfate: 2ClO2 + PhN(H)CSNH 2 + H2O → SO42- + PhN(H)CONH2 + 2Cl- + 2H+. In excess PTU, mixtures of sulfinic and sulfonic acids are formed. The reaction was followed spectrophotometrically by observing the formation of chlorine dioxide which is formed from the reaction of the reactive intermediate HOCl and chlorite: 2ClO2- + HOCl + H+ → 2ClO2(aq) + Cl- + H2O. The complexity of the ClO2 - - PTU reaction arises from the fact that the reaction of ClO 2 with PTU is slow enough to allow the accumulation of ClO 2 in the presence of PTU. Hence the formation of ClO2 was observed to be oligooscillatory with transient formation of ClO2 even in conditions of excess oxidant. The reaction showed complex acid dependence with acid catalysis in pH conditions higher than pKa of HClO 2 and acid retardation in pH conditions of less than 2.0. The rate of oxidation of PTU was given by -d[PTU]/dt = k1[ClO2 -][PTU] + k2[HClO2][PTU] with the rate law: -d[PTU]/d/ = [Cl(III)]τ[PTU]0/Ka1 + [H + ] [K 1Ka1 + k2[H + ]]; where [Cl(III)]T is the sum of chlorite and chlorous acid and Ka1 is the acid dissociation constant for chlorous acid. The following bimolecular rate constants were evaluated; k1= 31.5±2.3 M-1 s -1 and k2 = 114±7 M-1 s-1. The direct reaction of ClO2 with PTU was autocatalytic in low acid concentrations with a stoichiometric ratio of 8:5; 8ClO2 + 5PhN(H)CSNH2 + 9H2O - 5SO42- + 5PhN(H)CONH2 + 8Cl- + 18H+. The proposed mechanism implicates HOCl as a major intermediate whose autocatalytic production determined the observed global dynamics of the reaction. A comprehensive 29-reaction scheme is evoked to describe the complex reaction dynamics.
