Ultrasonic and photochemical degradation of chlorpropham and 3-chloroaniline in aqueous solution

Sonolysis and photolysis are compared for the transformation of chlorpropham, a systemic herbicide belonging to the carbamate group, and 3-chloroaniline, the main intermediate often observed in the degradation of chlorpropham. In both cases the ultrasonic degradation is much more efficient at 482 kHz than at 20 kHz. The main identified sonoproducts formed in the degradation of chlorpropham are 3-chloroaniline, formic acid, carbon monoxide and dioxide and chloride ions. The degradation of 3-chloroaniline also leads to Cl−, CO and CO2 but chlorohydroquine was also detected as an intermediate. Two different mechanisms are involved in the ultrasonic transformation: pyrolysis resulting from the implosion of cavitation microbubbles and oxidation by hydroxyl radicals formed by sonolysis of water. Photolysis is more specific: 3-chloroaniline is initially quantitatively transformed into 3-aminophenol. A heterolytic mechanism is suggested. Resorcinol and some unidentified photoproducts are formed in a second stage. The same type of reaction is involved in the photo-transformation of chlorpropham, but the reaction is not so specific. In both cases the photolysis at 254 nm leads to a complete disappearance of phenolic and quinonic compounds.