Elimination of alcohols to give alkenes using POCl3
Description: When treated with phosphorus oxychloride (POCl3) alcohols are converted to alkenes via an elimination reaction.
Notes: Note that the more substituted alkene is formed (Zaitsev product)
Notes: The purpose of pyridine is to perform the key elimination step. Note in the second and third examples that the most substituted alkene is formed (Zaitsev rule).
Mechanism: 1,2-addition of the alcohol oxygen to the phosphorus (Step 1, arrows A and B) is followed by 1,2-elimination of chloride (Step 2, arrows C and D). Finally, deprotonation of the carbon β to the OPOCl2 leads to an elimination (E2) to give the alkene (Step 3, arrows E, F, and G).
Notes: Pyridine is used to do the key elimination step. It would also be reasonable to show a proton transfer step from OH to O in between steps 1 and 2.