Polymer-supported reagents solvent considerations

Interestingly, the same reaction can be performed with the polymer-supported reagent 18 in water, because the reagent 18 was found to be considerably stable in this solvent. A mechanistic rationale of the catalytic activation of iodosobenzene 5 by potassium bromide is given in Scheme 14. This reaction provides a very facile and environmentally benign method for the alcohol oxidation. 

For chemical reactions on an insoluble polymer, dissolved reagents and washing media of maximal solvation power are needed to swell the cross-linked support. In peptide synthesis most of the reagents and solvents used are volatile, corrosive, and toxic. Therefore, these properties of the fluids also have to be taken in consideration during storage, pumping, and metering in a peptide synthesizer. 

The eco-friendly advantages of these reactions may be found in instances where catalytic amounts of reagents or supported agents are used since they provide reduction or elimination of solvents or utilize water as reaction media, thus preventing pollution at source . Although not delineated completely, the reaction rate enhancements achieved in these methods may be ascribable to non-thermal effects. The rationalization of microwave effects and mechanistic considerations possibly involving the intermediacy of polar transition states have been discussed.The use of synthesis processes that employ MW/ultrasonic irradiation to shorten the reaction time and eliminate or minimize side product formation is already finding acceptance in pharmaceutical industry (combinatorial chemistry) and polymer syntheses... 

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