Protecting groups modification with iodine

Although sulphenyl iodides are generally too reactive to be utilized for protective groups, the conversion of thiols to sulphenyl iodides by the action of iodine or iodine monochloride has been useful in certain situations [164, 165]. The reversible protection of a thiol group in lactic dehydrogenase was also accomplished [166] by treatment of the protein with mercury(ll) chloride. After chemical modification of a histidine residue the chloromercury group was removed by treatment with cysteine. The insoluble nature of these derivatives makes the heavy metal S-protective groups potentially less useful for smaller molecules. 

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