Kinetics and mechanism of the sonolytic degradation of CCl4: Intermediates and byproducts

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 x 10(-3) s(-1) when the initial CCl4 concentration, [CCl4](i), is 1.95 x 10(-4) mol L(-1) and increases slightly to 3.9 x 10(-3) s(-1) when [CCl4](i) = 1.95 x 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 CCl4.