The detailed kinetics of the reaction of toluidine blue {phenothiazine-5-ium, 3amino-7(dimethylamino)-2-methyl chloride, tolonium chloride, with potassium bro-ϩ Ϫ TB Cl } mate and with aqueous bromine reaction were studied. In most of the experiments, the kinetics were monitored by following the rat
Kinetics and simulations of reaction between safranine-O and acidic bromate and role of bromide therein
✍ Scribed by S. B. Jonnalagadda; M. Shezi; N. R. Gollapalli
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- English
- Weight
- 262 KB
- Volume
- 34
- Category
- Article
- ISSN
- 0538-8066
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✦ Synopsis
Abstract
Safranine‐O, a dye of the phenazinium class, was found to exhibit intricate kinetics during its reaction with bromate at low pH conditions. Under conditions of excess concentrations of acid and bromate, safranine‐O (SA^+^) initially depleted very slowly (k = (3.9 ± 0.3) × 10^−4^ M^−3^ s^−1^) but after an induction time, the reaction occurred swiftly. Bromide exhibited a dual role in the reaction mechanism, both as an autocatalyst and as an inhibitor. The added bromide increased the initial rate of depletion of SA^+^, but delayed the transition to rapid reaction. The overall stiochiometric reaction was found to be 6SA^+^ + 4 BrO~3~ ^−^ = 6SP + 3N~2~O + 3H~2~O + 6H^+^ + 4Br^−^, where SP is 3‐amino‐7‐oxo‐2,8‐dimethyl‐5‐phenylphenazine. The fast kinetics of the reaction between aqueous bromine and safranine‐O (k = (2.2 ± 0.1) × 10^3^ M^−1^ s^−1^) are also reported in this paper A 17‐step mechanism, consistent with the overall reaction dynamics and supported by simulations, is proposed and the role of various bromo and oxybromo species is also discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 542–549, 2002
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## Abstract At bromide concentrations higher than 0.1 M, a second term must be added to the classical rate law of the bromate–bromide reaction that becomes −d[BrO~3~^−^]/d__t__ = [BrO~3~^−^][H^+^]^2^(__k__~1~[Br^−^] + __k__~2~[Br^−^]^2^). In perchloric solutions at 25°C, __k__~1~ = 2.18 dm^3^ mol^−
The reaction has been studied spectrophotometrically monitoring the absorbance in the wavelength range. The spectra of the reactants, intermediates, and prod-240-400 nm ucts in this system are overlapping; thus special programs [1,2] have been used (and tested) to unravel the kinetics and mechanism
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