Reaction with halocarbons

EFFECT OF CARBON COATING ON AP-MGO REACTIONS WITH HALOCARBONS... 

We are not yet sure what causes the positive effect of the carbon coating on the performance of AP-MgO in the reactions with halocarbons. The carbon coating may adsorb some of the reaction products or impurities in the feed, that allows for a faster reaction of the halocarbons with the oxide core. Further studies including mass-spectrometric analysis of the gas phase composition are required. 

Nanocrystalline oxides have exceptionally high reactivity with respect to halocarbons. First of all, the temperature of their reaction with halocarbons is much lower than observed for bulk analogs. It is thus possible to carry out destructive adsorption reactions at fairly low temperatures. This is especially important for the development of effective destructive sorbents for neutralization of toxic compounds at mild temperatures. We have also demonstrated that nanocrystalline oxides can be used as precursors for the synthesis of novel halogenated nanocrystalline materials. 

Excited states of NOM (S ) can transfer electronic energy to or possibly can participate in redox reactions with halocarbons (eq 6). 

The reaction with halocarbons results in loss of halide, with concurrent Ibrmation of halocarbon-derived free radicals, R (eq 5) (47). Zepp and co-vorkers (12) used the photoproduction of chloride ions from the halocarbon, 2-chloroethanol, a known solvated electron scavenger, in solutions of NOM... 

Both types of hydridostannylsilane derivatives can be halogenated by the reaction with halocarbons (Eqs. 4 and 5). 

We have discussed primarily our own work, especially that which is still in progress. No discussion of pyridinyl radical Tr-mers would be complete without citing the discovery of the dimerization of pyridinyl radicals by Itoh and Nagakura (14) and the work of Ikegami (15) on different ir-mer triplets. The original impetus for the study of pyridinyl radical reaction with halocarbons was given by the discovery by Westhelmer, Kurz and Hutton (16) that dihy-dropyridines were converted into pyridinium compounds via free radical reactions in the presence of tetrachloromethane. An extensive review of pyridinyl radicals has been published elsewhere (IJ. New ways of measuring the low temperature spectra of pyridinyl radicals are under development (18). 

For completeness, it should be mentioned that the reaction of trifluoromethyl radicals to replace halogens is extremely general, and not confined solely to metal species. Plasma-generated trifluoromethyl radicals will react with halocarbons according to the reaction 21)... 

It is known that alumina is chlorinated exothermically at above 200° C by contact with halocarbon vapours, and hydrogen chloride, phosgene etc. are produced. It has now been found that a Co/Mo-alumina catalyst will generate a substantial exotherm in contact with vapour of carbon tetrachloride or 1,1,1-trichloroethane at ambient temperature in presence of air. In absence of air, the effect is less intense. Two successive phases appear to be involved first, adsorption raises the temperature of the alumina then reaction, presumably metal-catalysed, sets in with a further exotherm. 

As in the GAC experiments just described, many new halocarbons were formed by reaction with Ag (column 4, Table IV). Chlorination... 

Reaction with halogens and halocarbons commonly leads to replacement of the hydride with halide (equation 55) and often to subsequent oxidation as well. I2 is useful in giving a more selective oxidation in many cases (equation 56). 

The halocarbons, which are not destroyed in the troposphere by reactions with hydroxyl, pass into the stratosphere where they are photo-dissociated to liberate chlorine atoms which attack ozone. Only one of them is of natural origin, methyl chloride CH3CI, but there are also several industrial products, especially carbon tetrachloride, CC14, trichlorofluo-romethane, CFC13, and dichlorodifluoromethane. Methyl chloride (Table III) has a natural marine origin (for details, see ref. 12), but it is certainly present also in the smoke produced when polyvinyl and other products containing chlorine are burnt. In addition, it is produced naturally not only in forest fires, but also in tropical agriculture based on the cultivation... 

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