| Abstract
| - The kinetics of the reaction of H2O2 with excess SCN- in acidic media was studied by use of Ti(IV) as anindicator for the concentration of H2O2. Pseudo-first-order behavior was realized by this method, and these dataconfirm the acid-catalyzed rate law and rate constant reported some 40 years ago for this reaction under conditionsof excess H2O2. Under the same conditions except without Ti(IV), repetitive-scan spectra reveal the formationand decay of an intermediate that absorbs in the UV. In the proposed mechanism, HOSCN is produced in the firststep and it is converted rapidly to (SCN)2 through its equilibrium reaction with SCN-. The observed intermediateis believed to be (SCN)2, which decays on a longer time scale. Excellent global fits of this mechanism to therepetitive-scan data are obtained with rate constants constrained by the Ti(IV) data and published previously inour study of the ClO2/SCN- reaction. These fits yield a spectrum for (SCN)2 that is characterized by λmax = 297nm and ε297 = 147 M-1 cm-1, in fine agreement with our prior report.
- An intermediate is detected by UV spectrophotometry in the reaction of H2O2 with excess SCN- under strongly acidic conditions. Its spectrum and decay kinetics agree with the characteristics of an intermediate detected previously in the reaction of ClO2 with SCN-. The intermediate is identified as thiocyanogen (SCN)2.
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