Chlorinated alkanes

The most commonly used HPLC solvents in this class are dichlorom hane, chloroform, and carbon tetrachloride. All of these solvents, as well as most highly 

FIGURE 1.15 Free-radical formation. The fiee-iadical product of dichlorometfaane is extremely reactive. 

Because of their rapid breakdown process, chlorinated solvents are almost invariably sold containing a stabilizer. Dichloromethane has 25 ppm amylene (2-methyl-2-butene), cyclohexene, 400-600 ppm methanol, or a methanol/amylene blend as stabilizer. These alkenes act as chemical sinks that react with hydrochloric acid. Cyclohexane has also been used as a preservative but its efficacy is questionable. 

Chloroform stabilizers include ethanol (0.5-1%), amylene (50-150 ppm), and an ethanol/amylene blend. 

Carbon tetrachloride is an exception and is commonly produced without a preservative. The reason for this is that carbon tetrachloride is frequently used as an aprotic solvent for infrared analyses. Infrared quantitation of oil and grease levels through the intensity of the C-H stretch can be done using carbon tetrachloride. An alkene preservative would render it unsuitable for use. 

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In contrast with alkane chlorination, alkane bromination is usually much more selective. In its reaction with 2-methylpropane, for example, bromine abstracts the tertiary hydrogen with greater than 99% selectivity, as opposed to the 35 65 mixture observed in the corresponding chlorination. 

Murphy GL, JJ Perry (1983) Incorporation of chlorinated alkanes into fatty acids of hydrocarbon-utilizing mycobacteria. / BactcnoZ 156 1158-1164. 

The 50.31 MHz 13C NMR spectra of the chlorinated alkanes were recorded on a Varian XL-200 NMR spectrometer. The temperature for all measurements was 50 ° C. It was necessary to record 10 scans at each sampling point as the reduction proceeded. A delay of 30 s was employed between each scan. In order to verify the quantitative nature of the NMR data, carbon-13 Tj data were recorded for all materials using the standard 1800 - r -90 ° inversion-recovery sequence. Relaxation data were obtained on (n-Bu)3SnH, (n-Bu)3SnCl, DCP, TCH, pentane, and heptane under the same solvent and temperature conditions used in the reduction experiments. In addition, relaxation measurements were carried out on partially reduced (70%) samples of DCP and TCH in order to obtain T data on 2-chloropentane, 2,4-dichloroheptane, 2,6-dichloroheptane, 4-chloroheptane, and 2-chloroheptane. The results of these measurements are presented in Table II. In the NMR analysis of the chloroalkane reductions, we measured the intensity of carbon nuclei with T values such that a delay time of 30 s represents at least 3 Tj. The only exception to this is heptane where the shortest T[ is 12.3 s (delay = 2.5 ). However, the error generated would be less than 10%, and, in addition, heptane concentration can also be obtained by product difference measurements in the TCH reduction. Measurements of the nuclear Overhauser enhancement (NOE) for carbon nuclei in the model compounds indicate uniform and full enhancements for those nuclei used in the quantitative measurements. Table II also contains the chemical... 

Drouillard, K.G., Hiebert, T., Tran, P., Tomy, G.T., Muir. D.C.G., and Friesen, K.J. Estimating the aqueous solubilities of individual chlorinated n-alkanes (C10-C12) from measurements of chlorinated alkane mixtures. Environ. Toxicol. Chem., 17(7) 1261-1267, 1998. 

Chlorinated alkanes and aromatics Brominated neopentyl alcohol and derivatives Dibromophenol Flame retardants... 

Selan FM, Evans MA. 1987. The role of microtubules in chlorinated alkane- induced fatty liver. 

Chlorinated alkanes were used in the production of chlorofluoroalkanes (CFCs).188 Because of their atmospheric ozone-depleting ability, the use of CFCs is being phased out. Hydrochlorofluorocarbons, containing at least one hydrogen atom (HCFCs), are introduced as safer alternatives.189 190 In the long run, however, hydrofluorocarbons (HFCs) will be the ideal substitutes to CFCs.190... 

Interest in the bioremediation of chlorinated solvents is widespread. It is impractical to consider all the excellent efforts underway. An example will be given for both a chlorinated alkane and a chlorinated alkene. Both compounds, dichloromethane and trichloroethylene, are commonly used industrial solvents and degreasers that are important soil and water pollutants. 

Basak et al. [37] derived the following model for non-hydrogen-bonding compounds such as alkanes, alkylbenzenes, PAHs, chlorinated alkanes, chlorobenzenes, and PCBs ... 

The simplest chlorinated alkanes, alkenes, and alcohols (e.g., chloromethane, dichloromethane, chloroethane, 1,2-dichloroethane, vinyl chlonde, and 2-chloroethanol) serve as substrates for aerobic growth foi some, bacteria, but the majority of halogenated solvents cannot support growth. Nevertheless these compounds are mineralized under aerobic conditions. 

A correlation for chlorinated alkanes was also established using a as a descriptor. As discussed earlier, cf can be used to describe the behavior of aliphatic compounds. Figure 5.23 demonstrates the Hammett correlation for chlorinated alkanes. 

Hammett s correlation for rate constants of chlorinated alkanes reacting with hydroxyl radical. Experimental conditions elementary hydroxyl radical kinetic data, pH 9. 

A Hammett correlation was also established for chlorinated alkanes studied by UV/Ti02. The least substituted compound, ethane, was used as a reference compound. Figure 9.23 demonstrates the Hammett correlation for chlo-... 

Hammett s correlation for chlorinated alkanes studied by UV/Ti02. Experimental conditions 0.1 wt% TiOj 10 ppm initial concentration 20-mL reactor volume pH 7. 

Figure 9.25 shows the correlation coefficient of 0.9636 between the hydroxyl radical rate constants and UV/Ti02 rate constants for chlorinated alkanes. Therefore, the reaction mechanism for the degradation of chlorinated alkanes by UV/Ti02 is similar to the reaction with hydroxyl radical. This correlation suggests that the reaction proceeds via hydroxyl radical attack on the chlorinated alkane. 

Correlation between hydroxyl radical rate constants and UV/Ti02 rate constants for chlorinated alkanes. 

Chloroform Chlorinated Alkanes Hydrochloric acid, chlorine, 0.5-1% (v/v) ethanol... 

Brown et al. (1998), using whole needles of Pirns sylvestris (Scots pine), obtained a QSAR with very different coefficients for a very small series of chlorinated alkanes and alkenes ... 

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