Solvents and Alternate Reaction Media

Chemical reactions are often carried out in media, usually organic solvents or water, to provide a medium in which feedstocks and reagents can dissolve and come into close, rapid contact at the 

Heterogeneous catalyst I I on porous support or on reactor walls 

One approach to making chemical synthesis processes greener is to replace specific solvents with less hazardous ones. For this reason, toxic benzene solvent is replaced by toluene wherever possible. As shown by their structural formulas later in this section, toluene has a methyl group, -CH3, that benzene does not possess. The methyl group in toluene can be acted upon by human metabolic systems to produce a harmless metabolite (hippuric acid) that is eliminated in the urine, whereas metabolic processes acting upon benzene convert it to a toxic intermediate that can react with cellular DNA and cause blood abnormalities including leukemia. 

As another example of solvent replacement, -hexane, which can cause peripheral neuropathy in exposed individuals, can be replaced with 2,5-dimethylhexane, which does not cause this condition, for reactions in which the higher boiling temperature of the latter compound is not a problem. 

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