Non-Hydrolytic Decay of Formyl Chloride into CO and HCl in Aqueous Solution

Abstract

Formyl chloride has been generated in aqueous solution (i) by stopped-flow ozonation of vinyl chloride and (ii) by reacting dichloromethyl radicals with OH radicals using the pulse radiolysis technique. Vinyl chloride reacts in water with ozone (k = 1.7 × 104 dm3 mol-1 s-1, as determined by stopped-flow) yielding as final products (mol per mol of ozone) chloride ions (1.05), CO (1.01), and formate ions (0.06). Hydroxymethyl hydroperoxide (formaldehyde plus H2O2; 1.08) is also formed. HCl and formic acid are formed in less than 2 ms (the detection limit of the stopped-flow setup). At high pH the CO yield decreases (at pH 13.6 by 50%). It is concluded that the precursor of CO, HCl, and formic acid is formyl chloride. It predominantly decays into CO and HCl, and only at very high pH can hydrolysis to formic acid and HCl compete successfully. Using the pulse radiolysis technique dichloromethyl radicals are generated in Ar-saturated solutions from chloroform by reacting it with the solvated electron (originating from the radiolysis of water). The OH radicals (also from the radiolysis of water) partially react with the dichloromethyl radicals yielding dichloromethanol. Alternatively, dichloromethanol is generated in N2O-saturated solutions from dichloromethane, where some of the OH radicals are allowed to abstract an H atom from dichloromethane and another fraction to add to the dichloromethyl radicals. The observed conductivity changes are attributed to a very rapid decay (t 1/2 < 20 μs) of dichloromethanol into formyl chloride and HCl followed by the decay of formyl chloride into CO and HCl (k = 104 s-1). From these data and the decrease of the CO yield at high pH (ozonation of vinyl chloride) it is estimated that the OH--induced hydrolysis of formyl chloride occurs with a rate constant of ca. 2.5 × 104 dm3 mol-1 s-1.

Water‐Catalyzed Dehalogenation Reactions of the Isomer of CBr4 and Its Reaction Products and a Comparison to Analogous Reactions of the Isomers of Di‐ and Trihalomethanes

“…The HXCO species has been observed to decay mostly to CO + HX in the gas phase and decays much faster in aqueous solution, [50] consistent with the water-catalyzed reaction deduced from ab initio calculations for the CHBrO + n H 2 O!CO + HBr + n H 2 O reaction. The decomposition of X 2 CO species, such as Br 2 CO examined here, proceeds via two water-catalyzed steps with HBr leaving groups to decay to CO 2 + 2 HBr in the presence of water.…”

“…[23] Polyhalomethanes have also been used to study photochemical water treatment processes, to better understand the dehalogenation and decomposition of halogenated organic compounds, and to potentially help design and improve photocatalysts for water treatment. [24][25][26][27] Ultraviolet photolysis with the 253.7 nm line of a Hg lamp of low concentrations (< 10 À6 m) of trihalomethanes (e.g., CHBr 3 , CHBr 2 Cl, and CHCl 2 Br) in water was observed to lead to complete conversion of the halogens into their halide ions (bromide and/or chloride) with similar photoquantum yields of around 0.43. [24] We recently used a combination of photochemical experiments and theoretical calculations to help elucidate the reaction mechanism for photochemical conversion of low concentrations of CHBr 3 in water to three bromide ions.…”

“…[29,30] Other halomethanols such as CHCl 2 OH were experimentally observed to decompose into HClCO + HCl in the gas phase and to decompose much faster in aqueous solutions, consistent with water-assisted decomposition of halomethanols. [48][49][50] The closely related CCl 3 OH was found to decompose into CCl 2 O + HCl. [48] These experimental results are consistent with our present ab initio results for the water-assisted decomposition of CBr 3 OH into CBr 2 O + HBr and provide additional support for step 4 of our proposed reaction mechanism for decomposition of CBr 4 after photolysis in water.…”

Enhanced reductive degradation of carbon tetrachloride by biogenic vivianite and Fe(II)

“…Formate has been known to form above pH 13 through hydrolysis of :CCl 2 in solution after CO production (CO + OH À ! CHOO À ) (Dowideit et al, 1996). Danielsen and Hayes (2004) have proposed a possible reaction for the formation of formate in the range of pH 7-10 during the CT reduction by magnetite (Danielsen and Hayes, 2004).…”

A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

“…An analogous wall reaction of HCOCl also takes place on the chamber surface (Libuda et al, 1990;Kaiser and Wallington, 1994;Wallington et al, 1996). On the basis of experimental evidence that non-hydrolytic decay of HCOCl to give HCl+CO occurs quite rapidly in aqueous solutions (Dowideit et al, 1996), the reactive uptake coefficient of HCOCl on the surface of sea-salt aerosols is estimated to be 0.1 in the present work (see further discussion in Sect. S1 in the electronic supplement).…”