Pyridine-2-thione-N-oxycarbonyl

Another useful chain reaction involves the PTOC (pyridine-2-thione-N-oxycarbonyl) esters developed by Barton. Reaction of a carboxylic acid chloride (RCOCl) with the sodium salt on N-hydroxypyridine-2-thione produces an ester designated as R-PTOC. Addition of radical Y" (formed by an earUer initiation step) to the R-PTOC leads to the carboxy radical RCOj. The carboxy radical then decarboxylates to produce the radical R, which can continue the chain reaction or can undergo other reactions. 

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