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Mechanistic studies with positive iodine: Kinetics of oxidation of thiocyanate ion by iodine monochloride and aqueous iodine in perchloric acid medium
Author(s) -
Gowda B. Thimme,
Bhat J. Ishwara
Publication year - 1989
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550210803
Subject(s) - chemistry , perchloric acid , iodine monochloride , iodine , thiocyanate , arrhenius equation , inorganic chemistry , reaction rate constant , ionic strength , aqueous solution , kinetics , rate equation , ion , rate determining step , activation energy , organic chemistry , catalysis , physics , quantum mechanics
Kinetics of oxidation of thiocyanate ion (NCS − ) by iodine monochloride and iodine has been studied in aqueous perchloric acid medium. The rates of oxidations followed the rate laws:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {- \frac{{d[{\rm ICl]}}}{{dt}} = \frac{{k[{\rm ICl][NCS}^ -][{\rm H}^ +]}}{{l + {\rm K[NCS}^ -][{\rm H}^ +]}}} \\ {- \frac{{d[{\rm I}_{\rm 2}]}}{{dt}} = \frac{{k'[{\rm I}_{\rm 3} ^ -][{\rm NCS}^ -][{\rm H}^ +]}}{{[{\rm I}^ -][1 + {\rm K'[H}^ +]]}}{\rm at low [H}^ +]} \\ {{\rm and} - \frac{{d[{\rm I}_{\rm 2}]}}{{dt}} = \frac{{k''[{\rm I}_{\rm 2}]}}{{k'' + [{\rm H}^ +][{\rm I}^ -]}}{\rm at high [H}^ +]} \\ \end{array} $$\end{document} Variations in ionic strength and dielectric constant of the medium had little effects on the rates of reactions with both the oxidants. Mechanisms consistent with the observed rate laws have been suggested. Rate limiting steps have been identified and the constants of some of these steps have been evaluated by varying [NCS − ] at each temperature. Activation parameters were computed from the Arrhenius plots. The rate constants predicted from the rate law as [NCS − ], and [H + ], varied in iodine monochloride oxidation, are in good agreement with the experimental values providing support to the proposed mechanism.