HYDROLYSIS OF PHENYL PICOLINATE AT THE MINERAL WATER INTERFACE

As part of a study of the effect of mineral surfaces on the chemical transformation of organic chemicals, hydrolysis of a pesticide-like compound, phenyl picolinate (PHP) was examined in aqueous suspensions of amorphous silica (SiO2), gamma-aluminum oxide (Al2O3), anatase (TiO2), hematite (Fe2O3), and goethite (FeOOH) in the absence of light. TiO2 and FeOOH caused a significant increase in PHP hydrolysis rate in comparison to homogeneous solution. As the oxide loading increased, a corresponding increase in the rate of hydrolysis was observed. SiO2, Al2O3, and Fe2O3 exhibited no surface-catalyzed hydrolysis. Although the extent of PHP adsorption was small (less than 5% of total PHP), adsorption was necessary in order for surface-catalyzed hydrolysis to occur. Hydrolysis of the isomer phenyl isonicotinate was not promoted by any of the oxide surfaces examined. These results indicate that adsorption of PHP occurs through chelate formation with surface metal centers involving the heterocyclic nitrogen and the carbonyl oxygen. Surface chelate formation is not possible for phenyl isonicotinate. Surface chelate formation involving PHP activates the carbonyl carbon toward hydrolytic attack in a way similar to metal ion catalysis observed in homogeneous solution.