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 CCl 4 concentration, [CCl 4 ] i, is 1.95 × 10 - 4 mol L - 1 and increases slightly to 3.9 × 10 - 3 s - 1 when [CCl 4 ] 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, O 3 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 CCl 4 .