Showing papers by "Yong Du published in 2005"

Water-Catalyzed O−H Insertion/HI Elimination Reactions of Isodihalomethanes (CH2X−I, Where X = Cl, Br, I) with Water and the Dehalogenation of Dihalomethanes in Water-Solvated Environments

Abstract: A combined experimental and theoretical investigation of the ultraviolet photolysis of CH2XI (where X = Cl, Br, I) dihalomethanes in water is presented. Ultraviolet photolysis of low concentrations of CH2XI (where X = Cl, Br, I) in water appears to lead to almost complete conversion into CH2(OH)2 and HX and HI products. Picosecond time-resolved resonance Raman (ps-TR3) spectroscopy experiments revealed that noticeable amounts of CH2X−I isodihalomethane intermediates were formed within several picoseconds after photolysis of the CH2XI parent compound in mixed aqueous solutions. The ps-TR3 experiments in mixed aqueous solutions revealed that the decay of the CH2X−I isodihalomethane intermediates become significantly shorter as the water concentration increases, indicating that the CH2X−I intermediates may be reacting with water. Ab initio calculations found that the CH2X−I intermediates are able to react relatively easily with water via a water-catalyzed O−H insertion/HI elimination reaction to produce CH2X...

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

Abstract: A combined experimental and theoretical study of the UV photolysis of a typical tetrahalomethane, CBr 4 , in water and acetonitrile/water was performed. Ultraviolet photolysis of low concentrations of CBr 4 in water mostlyleads to the production of four HBr leaving groups and CO 2 . Picosecond time-resolved resonance Raman (Ps-TR 3 ) experiments and ab initio calculations indicate that water-catalyzed O-H insertion/HBr elimination of the isomer of CBr 4 and subsequent reactions of its products lead to the formation of these products. The UV photolyses of di-, tri-, and tetrahalomethanes at low concentrations in water-solvated environments are compared to one another. This comparison enables a general reaction scheme to be deduced that can account for the different products produced by UV photolysis of low concentrations of di-, tri-, and tetrahalomethanes in water. The fate of the (halo)formaldehyde intermediate in the chemical reaction mechanism is the key to determining how many strong acid leaving groups are produced and which carbon atom final product is likely formed by UV photolysis of a polyhalomethane at low concentrations in a water-solvated environment.

Ultraviolet photolysis of CH2I2 in methanol: O-H insertion and HI elimination reactions to form a dimethoxymethane product.

Abstract: Ultraviolet photolysis of low concentrations of CH2I2 in methanol solution found that CH2I2 is converted into dimethoxymethane and some H+ and I- products Picosecond time-resolved resonance Raman (ps-TR3) experiments observed that the isodiiodomethane (CH2I-I) photoproduct decayed faster as the concentration of methanol increases, suggesting that isodiiodomethane is reacting with methanol Ab initio calculations indicate isodiiodomethane is able to react with methanol via an O-H insertion/HI elimination to form an iodoether (ICH2-O-CH3) and HI products The iodoether can then further react via another O-H insertion/HI elimination reaction to form the dimethoxymethane (CH3-O-CH2-O-CH3) observed in the photochemistry experiments A reaction mechanism consistent with these experimental and theoretical observations is proposed

Comparison of the dehalogenation of dihalomethanes (CH2XI, where X = Cl, Br, I) following ultraviolet photolysis in aqueous and NaCl saltwater environments.

Abstract: The ultraviolet photolysis of low concentrations of CH2XI (X = Cl, Br, I) were investigated in water and saltwater solutions by photochemistry and picosecond time-resolved resonance Raman spectroscopy. Photolysis in both kinds of solutions formed mostly CH2(OH)2 and HI and HX products. However, photolysis of the CH2XI molecules in saltwater resulted in production of some CH2XCl products not observed in aqueous solutions without salt present. The appearance of these new products in saltwater solutions is accompanied by a decrease in the amount of CH2(OH)2, HI, and HX products compared to photolysis in aqueous solutions without salt present. The possible implications for photolysis of CH2XI and other polyhalomethanes in seawater and other salt aqueous environments compared to nonsaltwater solvated environments is briefly discussed.