Chloroform

About: Chloroform is a research topic. Over the lifetime, 4323 publications have been published within this topic receiving 51555 citations. The topic is also known as: Methane trichloride & 1,1,1-trichloromethane.

Chlorination of humic materials: byproduct formation and chemical interpretations

Abstract: Ten aquatic humic and fulvic acids were isolated and studied with respect to their reaction with chlorine. Yields of TOX, chloroform, trichloroacetic acid, dichloroacetic acid, dichloroacetonitrile, and 1,1,1-trichloropropanone were measured at pH 7 and 12. Humic acids produced higher concentrations than their corresponding fulvic acids of all byproducts except 1,1,1-trichloropropanone. Chlorine consumption and byproduct formation were related to fundamental chemical characteristics of the humic materials. A statistical model was proposed for activated aromatic content based on {sup 13}C NMR and base titration data. The values estimated from this model were found to be well correlated with chlorine consumption. Specific by-product formation was related to UV absorbance, nitrogen content, or the activated aromatic content.

Photolysis of chloroform and other organic molecules in aqueous titanium dioxide suspensions

Abstract: The photocatalytic degradation of chloroform has been investigated in aqueous suspensions of TiO_2 over the wavelength range of 310-380 nm. A detailed reaction mechanism has been proposed in which the rate-determining step is the reaction of surface-bound *OH with adsorbed CHCl_3. A pH-stat titration technique was developed for the measurement of the rates of degradation of chlorinated hydrocarbons. The quantum efficiency (Ф = 0.56 at ⋋ = 330 nm) of the degradation of CHCl_3, was found to be inversely proportional to the square root of the incident light intensity. This relationship can be explained in terms of a direct competition between a second-order recombination of surface-bound 'OH and the rate-determining reaction of surface-bound 'OH with CHCl_3. The rates of degradation of several electron donors have been correlated with their computed surface speciation. The results of this study show that the adsorption of electron donors and acceptors to the TiO_2 surface plays a more important role in determining the rate of the photocatalytic reactions than the effect of pH-dependent Fermi-level shifts.

Photocatalytic destruction of VOCs in the gas-phase using titanium dioxide

Abstract: The gas-phase photocatalytic destruction of 17 VOCs over illuminated titanium dioxide was investigated using a plug flow reactor with the following experimental conditions: 200 ml min−1 flow rate, 23% relative humidity, 21% oxygen and an organic compound concentration range of 400–600 ppmv. At steady state, high conversion yields were obtained for trichloroethylene (99.9%), isooctane (98.9%), acetone (98.5%), methanol (97.9%), methyl ethyl ketone (97.1%),t-butyl methyl ether (96.1%), dimethoxymethane (93.9%), methylene chloride (90.4%), methyl isopropyl ketone (88.5%), isopropanol (79.7%), chloroform (69.5%) and tetrachloroethylene (66.6%). However, the photodegradation of isopropylbenzene (30.3%), methyl chloroform (20.5%) and pyridine (15.8%) was not so efficient. Carbon tetrachloride photoreduction was investigated in the presence of methanol as an electron donor. It was observed that the presence of methanol results in higher degradation rates. No reaction byproducts were detected for all VOCs tested under the experimental set-up and conditions described. Also, long-term conversion was obtained for all tested compounds. Catalyst deactivation was detected with toluene only, but the activity was restored by illuminating the catalyst in the presence of hydrogen peroxide. The capacity of the process to destroy different classes of volatile organic compounds present in the atmosphere was demonstrated.

Chlorination of Phenols: Kinetics and Formation of Chloroform

Abstract: The kinetics of chlorination of several phenolic compounds and the corresponding formation of chloroform were investigated at room temperature. For the chlorination of phenolic compounds, second-order kinetics was observed, first-order in chlorine, and first-order in the phenolic compound. The rate constants of the reactions of HOCl with phenol and phenolate anion and the rate constant of the acid-catalyzed reaction were determined in the pH range 1-11. The second-order rate constants for the reaction HOCl + phenol varied between 0.02 and 0.52 M(-1) s(-1), for the reaction HOCl and phenolate between 8.46 x 10(1) and 2.71 x 10(4) M(-1) s(-1). The rate constant for the acid-catalyzed reaction varied between 0.37 M(-2) s(-1) to 6.4 x 10(3) M(-2) s(-1). Hammett-type correlations were obtained for the reaction of HOCl with phenolate (log(k) = 4.15-3.00 x sigma sigma) and the acid-catalyzed reaction of HOCl with phenol (log(k) = 2.37-4.26 x sigma sigma). The formation of chloroform could be interpreted with a second-order model, first-order in chlorine, and first-order in chloroform precursors. The corresponding rate constants varied between k > 100 M(-1) s(-1) for resorcinol to 0.026 M(-1) s(-1) for p-nitrophenol at pH 8.0. It was found that the rate-limiting step of chloroform formation is the chlorination of the chlorinated ketones. Yields of chloroform formation depend on the type and position of the substituents and varied between 2 and 95% based on the concentration of the phenol.