Organic Chemistry
Thionyl chloride is widely used in organic synthesis. For some applications, it requires purification. Classically, it converts carboxylic acids to acyl chlorides and alcohols to alkyl chlorides
It is preferred over other reagents such as phosphorus pentachloride because the products of the thionyl chloride reactions, HCl and SO2, are gaseous, which simplifies the purification of the product. This combination of high reactivity and and gaseous by-products makes thionyl chloride well suited to one pot synthesis. Examples of which include the synthesis of oxazoline rings and the Darzens reaction (shown below) which proceeds via an internal nucleophilic substitution.
Sulfonic acids react with thionyl chloride to produce sulfonyl chlorides. Sulfonyl chlorides have also been prepared from the direct reaction of the corresponding diazonium salt with thionyl chloride. Likewise, thionyl chloride will transform sulfinic acids into sulfinyl chlorides and phosphonic acids into phosphoryl chlorides. Thionyl chloride will react with primary formamides to form isocyanides. Amides will react with thionyl chloride to form imidoyl chlorides. However, primary amides under heating with thionyl chloride will continue on to form nitriles.
Thionyl chloride can also produce nitriles from amides via E2 elimination.
Read more about this topic: Thionyl Chloride, Applications
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