SINGLET MOLECULAR OXYGEN-MEDIATED PHOTOOXIDATION OF NITROPHENOLIC COMPOUNDS IN WATER-IN-OIL MICROEMULSIONS - A KINETIC-STUDY

The aerobic singlet molecular oxygen-mediated photooxidation of 2-nitr ophenol (2NP) and 4-methyl-2-nitrophenol (4M2NP) has been studied in w ater-in-oil (WIG) microemulsion media, The microemulsions used were so dium bis(2-ethylhexyl)sulfosuccinate (AOT)-heptane-water or benzylhexa decyldimethylammonium chloride (BHDC)-benzene-water. The kinetic profi le of the reaction was investigated as a function of variables such as (a) surfactant structure and concentration and (b) amount of water di spersed in the microemulsion. Rate constants for overall quenching (k( t)) and chemical reaction (k(r)) for the interaction of 2NP and 4M2NP with singlet molecular oxygen in the microemulsion media were determin ed. The quantum efficiencies for the nitro-derivatives' photooxidation (phi(r)) in both anionic and cationic W/O microemulsions are one to t wo orders of magnitude-larger than in aqueous solutions. A mechanism b ased on polarity effects and probe location in the microemulsions is p roposed in order to rationalize the results.