Photochemistry and Green Synthesis

Photochemistry can potentially provide an environmental-friendly and green approach to chemical synthesis however, the ability to scale-up such photochemical processes is marred with problems, which are mainly associated with the power of light sources. The fact that a large number of microreactors are manufactured in glass, quartz, or transparent polymers is ideal for conducting photochemical processes, as the path length of such reactors is small meaning that it is very easy to irradiate the reaction mixture within the channel. Compared to other examples of chemical synthesis in flow reactors, the number of photochemical transformations performed under flow conditions has until recently been very limited. Early examples included benzopinacol formation [1], synthesis of cycloaddition products [2], and photosensitized diastereodifferentiation [3]. 

Other than energy considerations, on which there is little comparative data, the most important green role for photochemistry is in improving atom economy. Although only a preliminary research result, an excellent example of this is the avoidance of the need for stoichiometric amounts of Lewis acid catalysts in the synthesis of some acylated aromatic compounds. Benzoquinone can be reacted with an aldehyde under a sunlamp to yield an acylhydroquinone in up to 88% yield. The alternative procedure would involve reaction of an acyl chloride with hydroquinone and a... 

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