Development of a group contribution method to predict the aqueous-phase reactivities of hydrated electrons with organic compounds

Abstract

Hydrated electrons produced in aqueous-phase advanced reduction processes (ARPs) effectively destroy oxidized forms of environmentally relevant organic contaminants, including alkyl halides. Although the rate constants of hydrated electrons with various organic compounds have been experimentally measured and compiled in the literature, no mechanistic prediction tools have been developed. Given that numerous organic compounds are used in commercial production, a prediction tool for the fate of organic compounds in the aqueous-phase ARPs will be useful. This study focused on developing a group contribution method for hydrated electrons (GCMe) to predict the second-order rate constants with aliphatic and aromatic compounds. The GCMe includes 262 organic compounds undergoing four major reaction mechanisms. The GCMe fragments the structure of a given functional group of an organic compound based on the base structure that represent the major reaction with hydrated electrons and the neighboring functional group(s) that impact the main reaction. A total of 37 group rate constants and 69 group contribution factors were calibrated with 189 experimentally determined rate constants of single functional group compounds. Then, the parameters were validated with 73 multiple functional group compounds. Overall, the accuracy of GCMe in predicting the rate constants is within a difference of a factor of two from the experimental values. This predictive tool requiring only structural information of compounds can be used to screen hundreds of compounds in the prior assessment for experimental investigation in ARPs.