Alcohol Conversion to Alkyl Halide (SOCl2)

Animated mechanism for the conversion of methanol to chloromethane with SOCl₂.

1. The nucleophilic oxygen of the alcohol attacks sulfur in an SN2 reaction, ejecting a Cl^- leaving group.
2. Pyridine (reaction solvent) acts as a base and deprotonates the positively charged intermediate, preventing the intermediate from reverting to starting materials.
3. Cl^- ion acts as a nucleophile to displace chlorosulfite (SO₂Cl^-), which is an excellent leaving group.

This reaction is very similar to the reaction of alcohols with PBr₃ or PCl₃ to yield alkyl halides.