Environmental issues chlorofluorocarbons

Selective dehydrochlorination of chlorofluorocarbons (CFCs) is a very important environmental issue, and the need to replace these detrimental, ozone-depleting compounds by benign hydrochlorofluorocarbons (HCFCs) and/or hydrofluorocarbons (MFCs) has stimulated intensive work on the subject [172-182]. Palladium has been the most extensively investigated catalytic metal in this reaction, but the moderate selectivity for CH2F2 exhibited by Pd/Si02 (40%) can be significantly increased, up to 95%, with a 20-40 at%. Au addition [180], and, in Pd/C, from 70% to 90% with Au addition [181,182]. 

The replacement of chlorofluorocarbon (CFC) propellants with the non-ozone-depleting hydrofluorocarbons (HFCs) merit mention for two reasons. First, it illustrates how environmental impact can be an important selection criterion at a time when green issues are high profile. Second, HFCs were developed and evaluated for safety and delivery capability by a consortium of pharmaceutical companies, with costs shared and evaluation programs defined by prior agreement between end-users and propellant manufacturers. Such collaboration could be employed usefully in the future to develop novel excipients for delivery or targeting. The benefits would undoubtedly accrue to all. 

Reduction in the volatile organic content (VOC) of coatings, contributed by the solvents present, is now required because solvents, principally hydrocarbons, contribute through a reaction chain to an increase in ground level pollution (photochemical ozone). The hole in the ozone layer in the stratosphere concerns chlorofluorocarbons (CFC) and is a very different issue. Also of concern to formulators is the removal of lead, chromium and cadmium, which are long term environmental pollutants in paint residues. 

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