The photocatalytic decomposition of chloroform by tetrachloroaurate(III)

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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.

Section: Introductionmentioning

confidence: 99%

Photodecomposition of Chloroform Catalyzed by Unmodified MCM‐41 Mesoporous Silica

Peña

Chan

Cohen

et al. 2014

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“…While these and other mechanisms lead to photocatalyzed decomposition, the situation is often complicated by a transformation of the original chlorometallate complex to another species under irradiation , which can greatly obscure mechanistic conclusions.…”

Section: Introductionmentioning

confidence: 99%

“…A complex that does appear to catalyze chloroform decomposition in this way is [Ru(bpy) 2 Cl 2 ] + , which, when excited, apparently oxidizes ClÀ to Cl (17). *Corresponding author email: phoggard@scu.edu (Patrick E. Hoggard) While these and other (1,4) mechanisms lead to photocatalyzed decomposition, the situation is often complicated by a transformation of the original chlorometallate complex to another species under irradiation (2)(3)(4)18), which can greatly obscure mechanistic conclusions.…”

Section: Introductionmentioning

confidence: 99%

“…Several chlorometallate complexes have been found to catalyze the photodecomposition of liquid chloroform , effectively raising the threshold wavelength for decomposition from ca 260 nm for neat chloroform, in some cases to well above 400 nm . Although the mechanism of catalysis appears to vary among the chlorometallate complexes, most of the mechanisms have in common the production of a radical, leading to the sequence of steps shown below.…”

Section: Introductionmentioning

confidence: 99%

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Photocatalysis of Chloroform Decomposition by the Hexachlororuthenate(IV) Ion

Chan

Peña

Segura

et al. 2012

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Dissolved hexachlororuthenate(IV) effectively catalyzes the photodecomposition of chloroform to hydrogen chloride and phosgene under near-UV (λ > 345 nm) irradiation, whereby RuCl6(2-) is not itself photocatalytically active, but is photochemically transformed into a species that is active, possibly RuCl5 (CHCl3 )(-) . Conversion to a photoactive species during irradiation is consistent with the acceleration of the decomposition rate during the early stages and with the apparent inverse dependence of the decomposition rate on the initial concentration of RuCl6(2-) . The displacement of Cl(-) by CHCl3 in the coordination sphere to create the photoactive species is consistent with the retardation of photodecomposition by both Cl(-) and H2 O. The much smaller photodecomposition rate in CDCl3 suggests that C-H bond dissociation occurs during the primary photochemical event, which is also consistent with the presence of a CHCl3 molecule in the first coordination sphere.

“…An alternative route to photodegradation consists of the photoreduction of the chloroalkane (12–16). In either case, radicals are created that react with oxygen to form peroxy radicals and hydroperoxides, leading to further decomposition through a chain process (17). Yet another means to effect photodecomposition is for the catalyst to undergo photoreduction by oxidizing a counterion or another substrate to create radicals, following which the catalyst is restored by a thermal process that may generate additional radicals (18).…”

Section: Introductionmentioning

confidence: 99%

Photocatalysis of Chloroform Decomposition by Hexachloroosmate(IV)

Peña¹,

Hoggard²

2010

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Hexachloroosmate(IV) effectively catalyzes the photodecomposition of chloroform in aerated solutions. The decomposition products are consistent with a mechanism in which excited state OsCl(6)(2-) reduces chloroform, rather than one involving photodissociation of chlorine atoms. Trace amounts of ethanol or water in the chloroform lead to photosubstitution to form OsCl(5)(EtOH)(-) or OsCl(5)(H(2)O)(-), neither of which is photocatalytically active.