Science of Synthesis

Härtinger, S.; Härtinger, M., Science of Synthesis, (2007) 35, 571.

The thermal halodecarboxylation of silver carboxylates is a radical-induced process commonly known as the Hunsdiecker reaction.[‌1‌,‌9‌,‌49‌–‌52‌] Anhydrous silver(I) salts ‌12‌ of high purity may be prepared by adding a slight excess of silver(I) oxide, with stirring, to an aqueous solution of the acid, followed by repeated evaporation and crystallization steps, and thorough drying over phosphorus pentoxide.[‌53‌] Alternatively, precipitates of ‌12‌ may be formed by adding a solution of silver(I) nitrate to a solution of a sodium carboxylate.[‌54‌] An anhydrous solution of the silver(I) salt in refluxing benzene, carbon tetrachloride, or petroleum ether is reacted with iodine to form an intermediate acyl hypoiodide (‌Scheme 4‌). Homolytic fission of the O—I bond affords a carboxylate radical which, after liberation of carbon dioxide, gives the corresponding iodoalkane ‌13‌.[‌55‌] The use of stoichiometric amounts of iodine is critical, since excess iodine may give rise to the formation of carboxylic esters by alkylation of salt ‌12‌.[‌50‌] The presence of trace amounts of water lead to the recovery of unchanged acid. Good product yields are obtained with salts of linear aliphatic acids[‌2‌,‌56‌–‌58‌] and bridged polycyclic acids.[‌59‌] More recent modifications of this method make use of organoiridium or -thallium systems,[‌55‌] or N-iodosuccinimide[‌60‌,‌61‌] as alternative sources of iodine.

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References

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• 8.Meeeee-Meee, (8888) 8/8, 888.