Conversion of alcohols to alkyl chlorides using SOCl2
Description: Primary or secondary alcohols can be converted into alkyl chlorides through treatment with SOCl2.
Notes: The byproducts of this reaction are sulfur dioxide (SO2) and HCl. This reaction will proceed with inversion of configuration.
Notes: Note that inversion of configuration occurred in example 3.
Mechanism: The oxygen atom of the alcohol performs a 1,2-addition on the sulfur (Step 1, arrows A and B) followed by 1,2-elimination of chloride ion (Step 2, arrows C and D). Attack of chloride ion on the carbon leads to an SN2 reaction (Step 3, arrows E and F) forming the alkyl chloride. (The chloride on the sulfur is then eliminated to form sulfur dioxide and HCl)
Notes: It’s also reasonable to show a proton transfer from the alcohol oxygen to the negative oxygen on sulfur after step 1 (but it’s a longer mechanism to draw).
One final (and annoying note). Although it’s often taught that this reaction proceeds through inversion (and SN2 reaction) in practice the tendency toward inversion can be solvent dependent. Consult “March’s Advanced Organic Chemistry” (editors March and Smith) for more details on this point.