THE PHOTOLYSIS OF POTASSIUM PEROXODISULFATE IN AQUEOUS-SOLUTION IN THE PRESENCE OF TERT-BUTANOL - A SIMPLE ACTINOMETER FOR 254 NM RADIATION

Aqueous potassium peroxodisulphate (0.01 mol dm-3) together with tert-butanol (0.1 mol dm-3) was photolysed with 254 nm light at 20-degrees-C. The peroxodisulphate ion is cleaved, giving rise to sulphate radicals SO4.-. These attack the tert-butanol under hydrogen abstraction and hydrogen sulphate formation. In deoxygenated solutions, PHI-(H+) = 1.4, PHI-(SO4(2-) = 1.4 and PHI-((HOC(CH3)2CH2)2) is approximately 0.7; in the presence of oxygen, PHI-(H+) = 1.8. The enhancement of PHI-(H+) by oxygen comes about through the production of superoxide via one of the bimolecular decay channels of the tert-butanol-derived peroxyl radical. The superoxide radical reduces S2O8(2-) under liberation of further SO4.-. The oxygenated peroxodisulphate-tert-butanol system is shown to constitute a straight-forward actinometer for 254 nm light. Some data and observations regarding the tert-butanol-free peroxodisulphate system are also presented.