Generation of singlet oxygen from the catalytic system H2O2/Ca(OH)2 and applications to the selective oxidation of unsaturated compounds

Abstract

Publisher Summary The usual way to generate 1O2 is photochemical, but many chemical reactions are also able to produce this excited species by decomposition of a peroxo compound. The screening experiments of the periodic classification revealed another particularly interesting chemical source of 1O2; the system H2O2/Ca(OH)2 that appears both attractive for its environmental friendly feature and amazing with respect to the simplicity of the catalyst involved. A detailed study of this system has been completed by confirming, in a first step, the generation of 1O2 by chemical trapping and by detection of its specific infrared (IR)-luminescence. Then, the kinetics of the reaction was examined by studying the influence of several parameters, such as pH and concentrations, and purities of reactants on the initial rate of 1O2 formation. Finally, the ability of this system to oxidize various water-soluble electron-rich substrates, such as polycyclic aromatic, cyclohexadienic, and acrylic derivatives, was assessed. The first aim of this study was to prove unambiguously the generation of 1O2 from the system H2O2/Ca(OH)2. One method used was the chemical trapping of this excited species. Because the current water-soluble chemical traps of 1O2 bear carboxylate or sulfonate functions, which are likely to interact with the calcium ions, a new cationic water-soluble trap was designed; the bis-(4'-trimethylphenylammonium)-9,10-anthracene dichloride 1 (BPAA). This trap reacts efficiently with 1O2, giving the endoperoxide BPAAO2. This trapping process competes with the solvent-induced quenching of 1O2.