ReviewCan fluorine chemistry be green chemistry?
Introduction
The main tenet of clean chemical synthesis, or green chemistry, is that a highly efficient chemical reaction which produces little or no waste is greatly preferable to treatment or recycling of effluent (see, for example [1]). In general, this means ensuring that as much of the substrate and reagents as possible find their way into the final product, and that the use of auxiliary compounds such as solvents and promoters is minimised or eliminated. Frequently, the conclusions are the same as those that would be reached from an economic point of view; less substrate, fewer reagents, less solvent and a consequent reduction in energy requirement will all contribute to financial savings.
Fluorine chemistry has an important role to play in clean technology, both in catalyst and solvent replacement technologies. Fluorine is a very light element and provides excellent value in terms of activity-per-gram. It is also recognised that fluorochemicals are frequently more effective and are required in smaller quantities than non-fluorinated compounds—in the case of fluorine, ‘less is more’. High effect, low dosage fluorinated formulations allow reductions in the use of materials and energy all along the production chain: less non-renewable feedstocks are consumed, transport and packaging is reduced, and the quantity of post-consumer waste is minimised. However, fluorochemicals have also been involved in some of the more negative aspects of the chemical industry. In this review article, we discuss some of the ways in which fluorine is involved in green chemistry.
Section snippets
Some problems with fluorine chemistry
One aspect of the chemical industry that has been subject to major change in recent years is the manufacture of halogenated organic molecules. Chlorofluorocarbons (CFCs), which were identified as having a significant contribution to the destruction of stratospheric ozone, through liberation of chlorine radicals via photolysis, were phased out as a result of the 1987 Montreal Protocol [2]. HCFCs were introduced as interim replacements for CFCs in refrigeration and blowing agent applications, and
Fluorous solvent technologies
It would be unfortunate if organofluorine compounds were to become the subject of such comprehensive restrictions that now affect chlorine-containing compounds, as the unique properties of fluorine give it an important role to play in the advancement of clean chemical synthesis. In particular, the immiscibility of compounds containing perfluoroalkyl groups with hydrocarbon and polar organic solvents has led to the development of fluorous biphasic chemistry, and other fluorous solvent
A case study: fluorination of aromatics
Fluoroaromatics are an important class of chemicals with applications including pharmaceuticals, agricultural chemicals, polymers and liquid crystals [26]. Out of several methods for producing fluoroaromatics, four of the most important—Halex, Balz-Schiemann, direct fluorination, and a recently reported route involving CuF2 (Scheme 6)—are discussed here in the context of their cost efficiency, risk, and other important criteria. An ideal synthesis for fluoroaromatics might involve a starting
Conclusions
Fluorine-containing compounds are found widely in the environment, and although some of these may be attributed to the activities of human beings in general, and the chemical industry in particular, their are also many natural processes contribute to fluorine reservoirs. Although certain fluorine-containing compounds have been identified as being involved in ozone depletion and global warming effects, legislative measures have been, or are being, put in place where necessary to reduce this
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