KINETICS, PRODUCTS, MECHANISMS AND QSARS FOR THE HYDROLYTIC TRANSFORMATION OF AROMATIC NITRILES IN ANAEROBIC SEDIMENT SLURRIES

The degradation of several substituted benzonitriles was examined in a naerobic sediment-water systems under laboratory conditions. Formation of the corresponding benzoic acids was the main transformation proces s taking place. The pseudo-first-order rate constants of this process were shown to depend on both the chemical structure of the starting co mpound and the sediment characteristics. The starting compounds were s elected with the aim of obtaining a maximum variation in chemical reac tivity and physical properties, and the sediments were selected with t he aim of assessing several environmental factors influencing the kine tics of transformation. Quantitative structure-activity relationships were developed for both ortho- and meta/para-substituted nitriles by r elating 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 o btained with the octanol/water partition coefficient of the nitriles a nd the summation of the inductive constants of the substituents as par ameters. The correlations were strongly enhanced by taking into accoun t 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 sedimen t samples did not differ significantly. Thus the obtained relationship s may be used to calculate rates of transformation of given aromatic n itriles in given sediment systems.