Photodecomposition of Chloroform Catalyzed by Unmodified MCM‐41 Mesoporous Silica

Abstract

Unactivated MCM-41 mesoporous silica catalyzes the photodecomposition of chloroform to phosgene and hydrogen chloride under near-UV (λ > 360 nm) irradiation. The rate of photodecomposition increases toward an asymptotic limit as the O(2) partial pressure is increased. Deuterochloroform does not decompose under the same experimental conditions. Low concentrations of both cyclohexane and ethanol quench the photodecomposition, whereas water, up to its solubility limit, does not. Dissolved tetraalkylammonium salts suppress photodecomposition. The data are consistent with a mechanism in which light absorption by an SiO(2) defect yields an electron-deficient oxygen atom, which then abstracts hydrogen from chloroform. The resulting CCl(3) radicals react with oxygen to form a peroxy radical that decomposes, eventually yielding phosgene and hydrogen chloride.

Heterogeneous Catalysis by Tetraethylammonium Tetrachloroferrate of the Photooxidation of Toluene by Visible and Near-UV Light

“…Photochemical reactions initiated by the photodissociation of chlorine atoms are typically accelerated in the presence of dissolved chloride or bromide ions [20,26,27], while other types of photoreactions involving metal complex excited states are sometimes retarded, or even quenched entirely [28,29]. The acceleration observed with reactions initiated by the photodissociation of chlorine atoms can be attributed to the formation of Cl 2 − ions, the equilibrium constant for which is approximately 2 × 10 5 in aqueous solution [30], and certainly larger in nonpolar solvents.…”

Phosphonate-substituted porphyrins as efficient, cost-effective and reusable photocatalysts

“…Porphyrins are usually only soluble in chlorinated solvents, which are toxic and can participate in radical processes, in particular in the presence of oxygen and catalysts. [15][16][17] This leads to decreased reaction selectivity and accelerated photocatalyst decomposition.…”