Chlorine selective

Alkanes can be simultaneously chlorinated and chlorosulfonated. This commercially useful reaction has been appHed to polyethylene (201—203). Aromatics can be chlorinated on the ring, and in the presence of a free-radical initiator alkylaromatic compounds can be chlorinated selectively in the side chain. King chlorination can be selective. A patent shows chlorination of 2,5-di- to 2,4,5-trichlorophenoxyacetic acid free of the toxic... 

A fact that can be put to preparative/synthetic use thus bromination of (CH3)3CH is found to yield only (CH3)3CBr (cf. chlorination, p.324). The effect is more pronounced when substituents are present that can stabilise the initial radical thus across the series, CH4, PhCH3, Ph2CH2 and Ph3CH the relative rates of bromination differ over a range of 109, but only over a range of 103 for chlorination. Selectivity decreases with rise of temperature, however. 

Applying this information to a typical diaphragm-cell tail gas, Fig. 7.4 shows the logarithm of the amount of unrecovered chlorine versus the relative membrane area required. Recovery of chlorine is not far from a first-order process. As chlorine selectively passes through the membrane, the partial pressures of the impurities increase in the remaining gas. This causes their rates of permeation to increase. The membrane area required for permeation of, say, 30% of the nitrogen is less than twice that required for 15%. 

Three different detection methods (gas chromatography with electron capture, mass spectrometric and atomic emission detectors) have been compared for the determination of polychlorobiphenyls in highly contaminated marine sediments [74], Only atomic emission detection in the chlorine-selective mode provided excellent polychlorobiphenyl profiles without interferences. However, the lower sensitivity of the atomic emission detector, compared to the other two detectors required a 10 to 20g sample size for most analyses. 

Remote chlorination (6, 298-300). Breslow has extended his remote functionalization of steroids to a double functionalization at C, and Cn of cholestanol. Thus the ester (2) of cholestanol, prepared from a p-iodophenylnicotinic acid, when treated with 1 (1.2 equiv.) is chlorinated selectively at C9 chlorination of the same ester with 3 equiv. of C6H5IC12 results in chlorination at C9 and at C17 in quantitative yield. The para-iodo group of the ester plays an important role in this remote chlorination. 

In the next example the bromine, being more reactive than chlorine, selectively reacts to form the Grignard reagent. The product alcohol is especially prone to El elimination (the carbocation would be stabilized by resonance), so the weak acid, ammonium chloride, is used in the workup step. 

The implication of this mechanism is that the most ideal catalyst under the most optimum conditions would transform six ethylene molecules into EO and one ethylene molecule into water and carbon dioxide. Hence, according to this theory, the selectivity can never exceed 6/7. This theory also explains the favourable influence of chlorine. It was known that chlorine selectively poisons sites on Ag which can adsorb O2 dissociatively. As atomic oxygen was considered to be... 

Aromatic solvents and carbon disulfide often increase the chlorination selectivity due to the formation of n- or O-complexes between the solvent molecules and the chlorine atom. Such an interaction decreases the reactivity and hence increases the selectivity toward the hydrogen atoms. For example, photochlorination of adamantane (461) gives a higher production of 1-chloroadamantane in CS2 than in benzene (Scheme 6.221).1302... 

A computer program has been developed to use the mass-selective detector as a chlorine-selective detector (LaBrosse and Anderegg 1984 Johnsen and Kolset 1988), but it does not appear to have been widely evaluated. Attention should be directed to three situations which may give rise to error in their application ... 

Johnsen, S. and K. Kolset. 1988. The mass-selective detector as a chlorine-selective detector.. Chromatogr. 438 233-242. 

LaBrosse, J.L. and R.J. Anderegg. 1984. The mass spectrometer as a chlorine-selective detector I. Description and evaluation of the technique. J. Chromatogr. 314 83-92. 

They gave on hydrogenolysis two epimeric 2-hydroxymethyl-3-tro-panols (XX and XXI), which could be chlorinated selectively to the... 

Another method for inverting or controlling stereochemistry is illustrated by conversion of (D)-mannitol to (/ )- or (S)-epi-chlorohydrin.l Stereocontrol was obtained by manipulating differences in reactivity. Tosyl diol 17 (obtained from (D)-mannitol) was chlorinated selectively at the more reactive primary alcohol to give... 

For example, /3-ionone can be chlorinated selectively in the apposition by addition of NCS to the kinetic enolate (eq 1). With the appropriate chiral auxiliary, NCS chlorinates silyl ketene acetals with high levels of diastereoselectivity (eq 2) a-Chloro... 

Reversed-phase SPE is applied principally in two areas of TEQA. The first application is in the determination of organochlorine pesticides (OCs) in connection with the determinative technique of GC using a chlorine-selective detector. The second application is in the determination of priority pollutant semivolatile organics that are adequately recovered from drinking water. Off-line RP-SPE coupled to a determinative technique such as GC using an element-selective detector is a very powerful combination with which to achieve the objectives of TEQA. To illustrate, this author s study of various organophosphorous pesticides (OPs) from spiked water using RP-SPE will now be discussed. 

Experiment 6 of Table 4 shows optimized results when chlorine was replaced with TCIA, showing that their use can be interchanged when appropriate. On a 10-g scale of the oxidation of [6] with chlorine (selectivity 52 1), l-hydroxy-9-octadecanone [7] was isolated in 74% yield in two crops of 99.5 and 98% purity, respectively (from ethanol). The oxidation of 1,12-octadecanediol [8] with TCIA on a 5- to 10-g scale was frequently incomplete, until acetone (20%) was used as a cosolvent to improve the solubilities. 

Figure 4.39 Bromine-vs-chlorine selectivity in polar/protic solvents is often better in absence...

Figure 4.40 Bromine-vs-chlorine selectivity in ethereal solvents is often insensitive to the presence of base...

They could demonstrate the facile hrranodemethylation of Cp (CO)2FeSiMe2SiMe3 with BBr3 selectively at the a-siUcon atom to produce Cp (CO)2FeSiBrMeSiMe3, and subsequently to Cp (CO)2FeSiBr2SiMc3 [412]. Similar activation had previously been observed by Malisch et al. in the reaction of Cp (CO)2FeSiH2SiH3, which was chlorinated selectively in a-position [413]. 

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