Green Chemistry by unknow

Author:unknow
Language: eng
Format: epub
ISBN: 9789811637469
Publisher: Springer Singapore

3.3.5 Fluorinated Biphasic Solvents

The first reaction using fluorinated alkanes as a reaction medium was carried out in 1993. A year later the term “fluorinated” became an analogue of the term “aqueous” with respect to fluorinated alkanes, esters, or amines. An example of used fluorinated solvents are perfluoromethylcyclohexane, perfluorohexane, etc. (Scheme 3.44).

Scheme 3.44Fluorinated solvents

Fluorinated Solvents (FS) are usually synthesized from the corresponding hydrocarbons by electrochemical fluorination or by using cobalt fluoride.

Fluorinated solvents are characterized by high density (usually 1.7–1.9 g/cm3) and low polarity, low solubility in water and organic solvents, high gas solubility (for example, the fluorine-containing Oxygent ™ emulsion is used to increase oxygen delivery to tissues and organs through the blood). They are chemically inert, nonexplosive, and low-toxic, do not destroy the ozone layer.

Since FSs are poorly miscible with organic solvents, they can be used in biphasic reactions where the reagent or catalyst are in the phase of the FS and are easily separated from the organic phase at the end of the reaction. In a number of cases, heating of the two-phase system leads to the formation of a homogeneous mixture in which the main reaction occurs, and then, as a result of cooling the system, the catalyst and reaction products are separated (Fig. 3.17). Such a method is particularly applicable in cases where a nonpolar compound is converted to a polar compound during the reaction. In this case, the more polar compound is formed, the lower its solubility in the phase of the FS.

Fig. 3.17Reaction using fluorinated solvents

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