Kinetics, products, mechanisms and QSARs for the hydrolytic transformation of aromatic nitriles in anaerobic sediment slurries

Abstract

The degradation of several substituted benzonitriles was examined in anaerobic sediment-water systems under laboratory conditions. Formation of the corresponding benzoic acids was the main transformation process taking place. The pseudo-first-order rate constants of this process were shown to depend on both the chemical structure of the starting compound and the sediment characteristics. The starting compounds were selected with the aim of obtaining a maximum variation in chemical reactivity and physical properties, and the sediments were selected with the aim of assessing several environmental factors influencing the kinetics of transformation. Quantitative structure-activity relationships were developed for both ortho- and meta/para-substituted nitriles by relating pseudo-first-order disappearance rate constants for reductive hydrolysis of 27 aromatic nitriles in anoxic sediment slurries to some readily available molecular descriptors. The best correlations were obtained with the octanol/water partition coefficient of the nitriles and the summation of the inductive constants of the substituents as parameters. The correlations were strongly enhanced by taking into account the fraction of the compounds sorbed to the solid phase. Also it was found that upon correction for sorption, rate constants for reductive hydrolysis of three substituted benzonitriles obtained in six sediment samples did not differ significantly. Thus the obtained relationships may be used to calculate rates of transformation of given aromatic nitriles in given sediment systems