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By W G Frankenberg

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Livingston and Bray (8,15) have considered this salt effect in some detail and have shown that it is of the order expected on the Bronsted theory. The iodide reaction was thought to be anomalous in that no salt effect could be observed (16). However, recent measurements by Wynne-Jones (17) indicate that this is because most of the work has been done in the region of ionic strength where the activity coefficients concerned are almost constant. At lower ionic strengths the expected variation is observed.

I n the cases of bromine and iodine (7,8) it has been possible to isolate reaction (1) or (2) from the other and obtain independent values of their rates. Many kinetic devices have been used, the results of which leave little doubt that the kinetics of (1) and (2) are the same at, or away from steady state conditions for all the halogens. 36 J. H. BAXENDALE i. Oxidation of Halides by Hydrogen Peroxide Consider first reaction (1). In the case of iodine the reaction is stoichiometric in acid solutions, and the early work of Magnanini (9) and Noyes (10) established that the rate of iodine formation is accurately expressed by the equation d[Iz]/dt = ki"[HzOz][I'] + ki[Hz0z1[I'I[H+] (a) where the value of k l o and kl are such that the H+ dependent term only becomes important in acidities greater than about 10V N (see Table I).

G) in terms of reaction through the hypohalite ion (reaction 5a), as proposed previously for the iodine reaction which shows the same kinetics a t high pH’s. Alternative schemes using Bray’s assumption of the intermediate HOOCl but involving the more probable ion displacement type of reaction and leading to the same kinetics would be: For Eq. (b), (e), or (f) + + + + HOz’ + ClOH HOOCl + OH’ HOOCl -+ H+ + + C1’ + HzOz HOz’ H+ HOz’ Clz Ft HOOCl C1’ 0 2 C1’ HOOCl + Hi + For Eq. ( d 0 2 42 J. H. BAXENDALE 6.

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