A comparison of the thermal and photochemical oxidation of 2‐propanol by two peroxoanions

Abstract

The chain length (i.e., relative quantum yield) for the oxidation of 2-propanol by peroxodisulfate ion at 25°C has been studied. A number of initial experiments were carried out in order to clarify the influence of dissolved oxygen, light intensity, cupric ion, and acetone absorption. After these problems were understood, conditions satisfactory for evaluation of chain length were chosen. The chain length was found to be 500 (to within &loo). The difference between this value and the thermal oxidation chain length of I800 at 60" is, in both direction and magnitude, as expected for a common mechanism and a low activation energy for the propagation steps. A remarkable difference is seen for comparable reactions of peroxodisulfate and peroxodiphosphate anions.

Persulfate and perphosphate oxidation of 2‐propanol: A relative rate study

“…radicals were effective in initiating a chain. As the pH was decreased (resulting in protonation of P2048-) it appeared that a chain became possible, as had also been observed [6,7] for the photochemical reaction. The stoichiometry for 2-propanol (RiCHOH) oxidation by both peroxides (symbolized ROOR) is ROOR + RiCHOH -2ROH + R;CO and the mechanism suggested [4] for the persulfate chain reaction is as follows:…”

Kinetics and mechanism of photochemical reactions of peroxomonosulfate in the presence and absence of 2‐propanol

“…The quantum yields for the photochemical reactions of isopropanol and H202 and isopropanol and P208-in alkaline medium (peroxodiphosphate exists as PzO$-) are approximately equal to 1.8 [19], which is lower than that observed for the corresponding photolytic reactions of PMS ( 4 = 4.45). The value of the photochemical chain length for the similar reaction of SzOi-was found [12] to be 500, which is enormously high compared to the values of the other peroxo salts. The reason attributed to the difference in quantum yields between S20;-and PzO$-is the difference in the reactivities of these peroxides with the isopropanol radical in the chain propagation reactions [1,191 (18) (19) S20;-+ (CH3)2COH + SO, + (CH&CO + HSO, P20:-+ (CH3)zCOH + HPO, + (CH3)2CO + POfIn the case of PMS a similar reason can be given for the higher value of the quantum yield (4 = 4.45) than that in the absence of isopropanol.…”

“…The value of 4 increased from 0.68 to 1.15 for [PMS] = 5-20 X 10-3M and remained constant for further increases of the concentration of PMS (Table I). It is interesting to note that the lowest value of 4 (0.68) was found to be equal to that found for the photochemical decomposition [1,12] of SzOg-, and the highest one was found to be greater than that found for the photochemical decomposition of H202 [ll]. Experiments conducted in the presence of added sulfate ions to find out the inhibiting effect, if there is any, exhibited no change in the quantum yield.…”

“…It is also interesting to study such reactions in the presence of additives like 2-propanol, with which SzOireacts with a chain length of 500 and more [12].…”

“…The quantum yield for the photolysis of H~0 2 was found to be unity [ll], which is higher than that of S20:-(4 = 0.6) [1, 12], and this is explained on the basis of chain reactions in H202 photolysis [ll]:…”