Chemical intermediates, CFCs

Several CFCs find use as chemical intermediates for the synthesis of other fluorine-containing compounds, notably fluorine-containing olefins. Some specialty applications include dielectric fluids, inert liquids, and brominated analogs used as fire extinguishants. 

Chlorofluoroearbons function as chemical intermediates, provided they are consumed rather than released into the atmosphere. CFC-113 serves as the starting material for the production of CTFE monomer. Despite the many years of research into a catalytic vapor-phase process for this conversion, the preferred current method still involves zinc dechlorination in methanol [reaction... 

Hydrdechlorination (HDC) is to be not only a process for a safe disposal of chlorofluorocarbons (CFCs) but also effective in preparation of useful chemical intermediates. Palladium based catalysts have been found to be very promising in the HDC reactions. It is observed that the nature of support used for the palladium catalysts has a role to play in modifying the selectivity towards useful products. In the present investigation, the influence of modification of the alumina support on the activity and selectivity of Pd catalysts during the HDC of CFC-113 is reported. 

Free-radical chain reactions also occur during the chlorination of methane (Chapter 10) and of the methyl group of methylbenzene. Ozone depletion by chlorofluorocarbons (CFCs), acid rain formation and formation of photochemical smog (Chapter 25 on the accompanying website) also involve free-radical reactions. (Free-radical reactions are also operating in unpolluted atmospheres and play an important role in all chemical reactions that occur in the gas phase.) The combustion of hydrocarbons, such as petrol, also proceeds via a free-radical mechanism, which has important consequences for the smooth running and performance of combustion engines. Chain reactions may also have ions as intermediates, as opposed to free radicals. 

As discussed in greater detail in Chapter 7 with respect to atmospheric reactions of air pollutants, hydroxyl radical, HO-, is the most important reactive intermediate in atmospheric chemical reactions. Ultraviolet radiation is very much involved in the formation of hydroxyl radical through various photochemical reactions, and depletion of UV-absorbing stratospheric ozone may increase the levels of this species. The HO- radical is very active in determining the fates of atmospheric methane, carbon monoxide, hydrochlorofluorocarbons and hydrofluorocarbons that are substitutes for ozone-depleting CFCs, and other gases relevant to climate and ozone levels, and it is very much involved in the formation and dissipation of photochemical smog (see Chapter 7, Section 7.8). 

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