How would you convert cyclohexanol to chlorocyclohexane?
Dehydrate the alcohol; treat the resultant cyclohexene with
The first reaction uses some source of acid (usually phosphoric acid) and heat to dehydrate the alcohol and form cyclohexene. Once you have the olefin, hydrohalogenation is facile.
An alternative way to do it is to use thionyl chloride in pyridine. It still works pretty well, despite the greater steric hindrance on cyclohexanol than a primary alcohol, and it is only one synthesis step.
The reaction is shown at the top, and the mechanism branches from the reactant from the top left.
- The carbonyl is electrophilic at the sulfur, so the thionyl chloride binds with the alcohol.
- Pyridine acts as a solvent that removes the proton.
- The tetrahedral "dichlorothioxyether" intermediate then collapses and one chloride leaves.
- That chloride then acts as a nucleophile and backside-attacks at the now-electrophilic carbon due to the inductive nature of the chlorine on the "chlorothioether" intermediate.