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
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Org. Synth. 1923, 3, 75
DOI Link: 10.15227/orgsyn.003.0075
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Org. Synth. 1930, 10, 88
DOI Link: 10.15227/orgsyn.010.0088
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Org. Synth. 1930, 10, 78
DOI Link: 10.15227/orgsyn.010.0078
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Org. Synth. 1949, 29, 33
DOI Link: 10.15227/orgsyn.029.0033
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Org. Synth. 1956, 36, 3
DOI Link: 10.15227/orgsyn.036.0003
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In this example electrons from C=O leave to bind to the Sulfur but I have also seen examples where electrons come from the oxygen in the alcohol or from the resonance form. Are all equally correct?
C=O is fine, the resonance form is fine
Using a pair of electrons from OH is not as good, since the resulting intermediate will not have two good resonance forms. It’s a pretty minor point though
can you not use PBr3 to do this aswell?
Yes – you could use PBr3 to make an acid bromide.
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).