Conversion of carboxylic acids into acid chlorides with SOCl2
Description: Thionyl chloride converts carboxylic acids into acid chlorides. The reaction liberates HCl and SO2 gas.
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Real-World Examples:
Org. Synth. 1929, 9, 32
DOI Link: 10.15227/orgsyn.009.0032


Org. Synth. 1923, 3, 75
DOI Link: 10.15227/orgsyn.003.0075


Org. Synth. 1930, 10, 88
DOI Link: 10.15227/orgsyn.010.0088


Org. Synth. 1930, 10, 78
DOI Link: 10.15227/orgsyn.010.0078


Org. Synth. 1949, 29, 33
DOI Link: 10.15227/orgsyn.029.0033


Org. Synth. 1956, 36, 3
DOI Link: 10.15227/orgsyn.036.0003


What kind of solution should this reaction be done in?
It’s often done in thionyl chloride as solvent. See the Org Syn reference. http://www.orgsyn.org/demo.aspx?prep=CV1P0147
(note that these days it’s more common to use oxalyl chloride w/ DMF as a catalyst under Vilsmeier conditions).
can you not use PBr3 to do this aswell?
Yes – you could use PBr3 to make an acid bromide.