Kinetics and Mechanism of the Sonolytic Degradation of CCl4: Intermediates and Byproducts

Abstract

The sonolytic degradation of aqueous carbon tetrachloride is investigated at a sound frequency of 20 kHz and 135 W (112.5 W cm-2) of power. The observed first-order degradation rate constant in an Ar-saturated solution is 3.3 × 10-3 s-1 when the initial CCl4 concentration, [CCl4]i, is 1.95 × 10-4 mol L-1 and increases slightly to 3.9 × 10-3 s-1 when [CCl4]i = 1.95 × 10-5 mol L-1. Low concentrations (10-8−10-7 mol L-1) of the organic byproducts, hexachloroethane and tetrachloroethylene, are detected, as well as the inorganic products chloride ion and hypochlorous acid. The chlorine mass balance after sonolysis is determined to be >70%. The reactive intermediate, dichlorocarbene, is identified and quantified by means of trapping with 2,3-dimethyl-2-butene. The presence of ozone in the sonicated solution does not significantly effect the rate of degradation of carbon tetrachloride; however, O3 inhibits the accumulation of hexachloroethane and tetrachloroethylene. Ultrasonic irradiation of an aqueous mixture of p-nitrophenol (p-NP) and carbon tetrachloride results in the acceleration of the sonochemical degradation of p-NP. The sonolytic rate of degradation of p-NP appears to be enhanced by the presence of hypochlorous acid, which results from the sonolysis of CCl4.