Sb. Jonnalagadda et al., OXYHALOGEN-SULFUR CHEMISTRY - BROMATE OXIDATION OF 1-METHYL-2-THIOUREA IN ACIDIC MEDIUM, Journal of physical chemistry, 100(32), 1996, pp. 13521-13530
The reaction between bromate and 1-methyl-2-thiourea, CH3NH(NH2)C = S
(MTU), has been studied in acidic medium. The stoichiometry of the rea
ction in excess MTU has been established as 4BrO(3)(-) + 3CH(3)NH(NH2)
C = S + S + 3H(2)O --> 4Br(-) + 3SO(4)(2-) + 3CH(3)NH(NH2)C = O + 6H() (A); and in excess bromate the stoichiometry is: 8BrO(3)(-) + 5CH(3)
NH(NH2)C = S + H2O --> 4Br(2) + 5SO(4)(2-) + 5CH(3)NH(NH2)C = O + 2H() (B). Stoichiometry B includes the oxidation of MTU (stoichiometry A)
and the oxidation of Br- by the excess BrO3- : BrO3- + 5Br(-) + 6H(+)
--> 3Br(2) + 3H(2)O. In excess BrO3- the reaction is characterized by
an induction period followed by formation of Br-2 The reaction betwee
n Br-2 and MTU is very fast with a bimolecular lower limit rate consta
nt of 2.0 x 10(6) M(-1) s(-1) such that the formation of Br-2 is an in
dicator for the complete consumption of MTU. The reaction could be fol
lowed by monitoring the depletion of MTU through its absorbance at lam
bda = 239 nm or the formation of Br-2 at lambda = 390 nm. The rate of
reaction was deduced as -d[BrO3-]/dt = k(0)[BrO3-][MTU][H+](2) with k(
0) = 14.7 +/- 1.2 M(-3) s(-1). A proposed 17-step reaction mechanism g
ives good agreement between experimental data and computer simulations
.