The
activation of persulfate by phenols was investigated to further
the understanding of persulfate chemistry for in situ chemical oxidation
(ISCO). Phenol (p<i>K</i><sub>a</sub> = 10.0) activated
persulfate at pH 12 but not at pH 8, suggesting activation occurred
only via the phenoxide form. Evaluation of the phenoxide activation
mechanism was complicated by the concurrent activation of persulfate
by hydroperoxide anion, which is generated by the base catalyzed hydrolysis
of persulfate. Therefore, phenoxide activation was investigated using
pentachlorophenoxide at pH 8.3, midway between the p<i>K</i><sub>a</sub> of pentachlorophenol (p<i>K</i><sub>a</sub> = 4.8) and that of hydrogen peroxide (p<i>K</i><sub>a</sub> = 11.8). Of the two possible mechanisms for phenoxide activation
of persulfate (reduction or nucleophilic attack) the results were
consistent with reduction of persulfate by phenoxide with oxidation
of the phenoxide. The concentration of phenoxide required for maximum
persulfate activation was low (1 mM). The results of this research
document that phenoxides activate persulfate via reduction; phenolic
moieties ubiquitous to soil organic matter in the subsurface may have
a significant role in the activation of persulfate during its injection
into the subsurface for ISCO. Furthermore, the results provide the
foundation for activation of persulfate by other organic anions without
the toxicity of phenols, such as keto acids