MECHANISTIC AND KINETIC-STUDIES OF THE PHOTODEGRADATION OF BENZ[A]ANTHRACENE IN THE PRESENCE OF METHOXYPHENOLS

Kinetic studies were employed to assess an empirical rate law describi ng the rate of photodegradation of polycyclic aromatic hydrocarbons (P AH) in the presence of substituted methoxyphenols. A solution of benz[ a]anthracene (BaA) and vanillin in toluene was chosen as the model sys tem. A rate law and corresponding rate constants were determined for t his system: -d[BaA]/dt = k(A)[BaA] + k(B)[BaA][vanillin], where k(A) = 0.024 +/- 0.005 h-1 and k(B) = 81.17 +/- 3.19 M-1 h-1. Further experi ments using structure-reactivity relationships were applied to the mod el system to investigate the mechanism for BaA photodegradation. Data from these experiments suggest that the rate-determining step in the m echanism is hydrogen abstraction of the phenolic hydrogen from vanilli n. The photochemical reaction between PAH and methoxyphenols is most l ikely a very important degradation pathway for PAH associated with woo d combustion aerosol.