Photolysis of 2-Chlorophenol Dissolved in Surfactant Solutions

Abstract

The photochemical degradation and dechlorination of 2-chlorophenol (2CP) (0.1 g/L) dissolved in surfactant solutions has been studied. The initial degradation and dechlorination of 2CP followed apparent first-order kinetics in nearly all the test solutions. The quantum yields of 2CP degradation and dechlorination were enhanced in the presence of nonionic surfactant Brij 35 and anionic surfactant sodium dodecyl sulfate (SDS). A larger enhancement was observed at surfactant concentrations greater than the critical micelle concentration (cmc) and was attributed to partitioning of 2CP into the micelles. Furthermore, the study of 2CP photolysis in hexane, methanol, and dimethoxyethane suggested that the surfactant can serve as a hydrogen atom source in promoting 2CP degradation. Two 2CP phototransformation pathways in surfactant solutions were identified. The electronically excited anionic form of 2CP led to cyclopentadienecarboxylic acid formation through a ring contraction via the Wolff rearrangement. Electronic excitation of the undissociated form of 2CP led to the formation of catechol via a nucleophilic displacement of chloride in the presence of water. Phenol also observed as a photoproduct in non-nucleophilic solvents that can act as hydrogen atom donors. Phenol was also demonstrated to sensitize the 2CP transformation to phenol in micellar media.

Mechanistic aspects of photocatalytic activity of metalloporphyrin–titanium mixtures in microemulsions

“…23,34,35 The interaction of light with titanium dioxide, porphyrin or a mixture of them, promotes the generation of activated oxygen, mainly hydroxyl radicals and singlet oxygen species. Those radicals attack organic matter causing its degradation.…”

Electrochemical Dechlorination of 2-Chlorophenol on Pd/Ti, Ni/Ti and Pd-Ni Alloy/Ti Electrodes

“…1,2 Nowadays, the accumulation of this chlorinated aromatic compound in the environment is an urgent problem that needs solving. 2-CP is very slowly consumed by microorganisms and is difficult to treat with conventional microbiological technologies.…”

Environmental Implications of the Surfactant Effect on the Photochemistry of (Substituted) 4‐Chlorophenols in Water

“…), thus in a concentration above their critical micelle concentration (cmc), [18] and phenols 1-3 in the range 2-4 10 À4 m, chosen because this allowed effective micelles incorporation. Irradiations were carried out under both deaerated and aerated conditions in neat water in the absence or in the presence of the chosen surfactant.…”

“…After 4 h irradiation, 4-chlorophenol was partially consumed (37 %) with the same product distribution as when an UV lamp was used. When 4 was added in 10 À3 m amount (eight times lower than its cmc), [18] some phenol was formed (ca. 15 %) but 1 b was by far the main product.…”

“…These pieces of evidence support that the primary photochemical reaction remains the same in micelles as in neat water, despite the very large www.chemsuschem.org change in product distribution toward a clean dechlorination, particularly with compounds 2 and 3, which occurred independent of the surfactant (up to 90 % with 3, a result similar to what was reported for the case of 2-chlorophenol). [18] The mechanism depicted in Scheme 5 can thus be proposed. Reasonably, chlorophenols molecules are disposed in the micelles with the polar OH group pointed towards the aqueous medium.…”