Abstract
The oxidation of Tween-80 by chromium(VI) in aqueous acidic solutions has been studied at different temperatures (30-60 degrees C). The rates of disappearance of chromium(VI) absorbance follow second order kinetics; first order each in [Cr(VI)] and [Tw-80] at constant acidity. The reaction order with respect to [H+] increases from one to higher with increase in [HClO4]. Interestingly, Tw-80 is not oxidised in absence of acid. The reaction is considered to proceed through the formation of a chromate ester between the chromium(VI) and primary -OH group of polyoxyethylene chain of Tw-80. The activation parameters calculated using Arrhenius and Eyring equations are: E-a = 46 kJ mol(-1), Delta H-# = 44 kJ mol(-1) and Delta S-# = -200JK-(1) mol(-1). A mechanism consistent with the results obtained has been proposed with the following rate equation:
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