Development of a structure-reactivity relationship for the photohydrolysis of substituted aromatic halides

Abstract

Rates of photodegradation of 13 structurally related 1,3-di-and 1,3,5-trisubstituted halogenated benzene derivatives in dilute aqueous solution were measured in the laboratory at wavelengths ranging from 250 to 360 nm. As shown by mathematical simulations of the reaction rate constants involved, photohydrolysis of all compounds studied is the main transformation process, generally accounting for over 95% of the amount of starting material removed. Quantum yields of this process were calculated using 3-chlorophenol as a reference, taking into account both the absorption characteristics of the compounds studied and the spectral energy distribution of the light source used. In an attempt to develop a structure-reactivity relationship, measured quantum yields of photohydrolysis were correlated to a number of readily available molecular descriptors. As shown by statistical analysis, the best correlation was obtained using a combination of the following descriptors: (1) the carbon-halogen bond strength and (2) the summation of the steric factors of all substituents.

Removal of selected pharmaceuticals in waters by photochemical processes

“…This procedure is reliable when measuring the rates of fast reactions in aqueous solutions, with overall second-order kinetics, and firstorder with respect to both reactants (the micropollutant and the oxidant). 14,22 By taking these considerations into account, the model proposes the following rate equation for the elimination of the reference compound:…”

Quantitative structure–property relationships (QSPRs) on direct photolysis of PCDDs

“…Direct photolysis can take place only if a photon is absorbed by a compound, leading to bond cleavage or rearrangement to form a new, stable product. It was found that most environmental photochemical reactions follow pseudo-®rst-order kinetics (Zepp and Schlotzhauer, 1979;Zepp, 1982;Dulin et al, 1986;Choudhry and Webster, 1989;Peijnenburg et al, 1992;Larson and Weber, 1994). Photolysis rate constants and quantum yields are two key parameters characterizing photochemical reactions of organic pollutants.…”

“…With regard to QSPRs on photolysis, in 1992, Peijnenburg et al (1992) reported ®rstly a QSPR model on direct photolysis quantum yields of selected meta-substituted halobenzenes under irradiation of arti®cial light sources. Chen et al (1998) were the ®rst to report on a QSPR model for photolysis rate constants of selected polycyclic aromatic hydrocarbons (PAHs) under irradiation of arti®cial light sources.…”

Modeling of photooxidation of acetamide herbicides in natural waters by UV radiation and the combinations UV/H2O2 and UV/O3

“…This competitive method has been previously used with success by several authors in photochemical studies of organic compounds. 24,25 Thus, and according to the considerations of Peijnemburg et al, 24 the photolysis rate given by eqn (3) also holds when two or more compounds are simultaneously photodegraded. Then the rate expressions for a specific couple of solutes can be written in the form:…”