[darkdevil]

Greetings,

Are there any convenient ways to make acid halides from carboxylic acids? I tried PBr3 with an acid, and I still need to remove the acid bromide by distillation.

Is thionyl chloride a good method to do so? since it's final byproduct is an inorganic acid and a gas SO2?? is there other ways too?

Can I react Sulfuryl chloride with an aldehyde to give an acid halide? I read the Wiki of sulfuryl chloride and it says "SO2Cl2 is widely used as a reagent in the conversion of C-H → C-Cl adjacent to activating substituents such as carbonyls and sulfoxides".

Thank you!

[discodermolide]

Thionyl chloride. Both by products are gases, HCl and SO₂. Do it at reflux temp. and they will disappear up the chimney.
You don't need a solvent, just do the whole thing in SOCl₂. At the end evaporate the excess thionyl chloride, and distill or crystallise or react your acid chloride.
PBr₃ usually brominates the alpha carbon of the acid, see Hell-Vollhardt-Zelinsky reactions.

[darkdevil]

Thionyl chloride. Both by products are gases, HCl and SO₂. Do it at reflux temp. and they will disappear up the chimney.
You don't need a solvent, just do the whole thing in SOCl₂. At the end evaporate the excess thionyl chloride, and distill or crystallise or react your acid chloride.
PBr₃ usually brominates the alpha carbon of the acid, see Hell-Vollhardt-Zelinsky reactions.

Thank you for you suggestions Discodermolide!

[Dan]

I've used oxalyl chloride with cat. DMF a few times to generate acyl chlorides for amide synthesis. I just injected the crude reaction mixture into a solution of the amine coupling partner once the acyl chloride formation was complete. Workup was just a couple of aqueous washes, usually >90% yield and clean by NMR.

[orgopete]

I've used oxalyl chloride with cat. DMF a few times to generate acyl chlorides for amide synthesis. I just injected the crude reaction mixture into a solution of the amine coupling partner once the acyl chloride formation was complete. Workup was just a couple of aqueous washes, usually >90% yield and clean by NMR.

Without searching for prior references (Fieser & Fieser?), I believe catalytic DMF can be used effectively with several reagents, oxalyl, thionyl, or phosphoryl chloride, or phosgene. The imidoyl chloride is an effective reagent generated in situ.

[Babcock_Hall]

Should old thionyl chloride be distilled or discarded?