Micellar effect on the photosensitized debromination of 2,3-dibromo-3-phenylpropionic acid. Control of forward and back electron transfers

Abstract

The zinc tetraphenylporphyrin (ZnTPP)- and zinc tetrasodiumtetra(p-sulphonatophenyl)porphyrin (ZnTPPS)-sensitized photodebromination of 2,3-dibromo-3-phenylpropionic acid (1) in the presence of a sacrificial reductant yielding cinnamic acid has been studied in cationic cetyltrimethylammonium bromide (CTAB) micellar solution. The photosensitized electron transfer and the resultant debromination are significantly affected by the solubilizing sites of sensitizer and dibromide (1) in the micelle. The debromination proceeds most efficiently when the anionic sensitizer and (1) are adsorbed on the cationic micellar surface. The overall efficiency is controlled mostly by the back electron transfer rather than the forward one, which is competitive with the subsequent debromination steps. The cationic micellar surface is effective for the electron-transfer debromination when both or either of the sensitizers is anionically charged.