Elimination of alcohols to give alkenes using POCl3
Description: When treated with phosphorus oxychloride (POCl3) alcohols are converted to alkenes via an elimination reaction.
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Notes: Note that the more substituted alkene is formed (Zaitsev product)
Examples:
Notes: Note that in all cases the byproducts are HCl and HOP(O)Cl2.
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.
Notes: Other bases could reasonably be used beside Cl(-) here. It would also be reasonable to show a proton transfer step from OH to O in between steps 1 and 2.
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Please forgive if this is an elementary question, but I am trying to extract information that was last used when a 128k Macintosh was 1600.00. The POCl3 : the electronegativities sandwich the poor little P between a rock and a hard place. The Cl wants the density in 3 directions but the O wants it more by .97. Without getting into the vector analysis, will the Cl’s be pulled upward in the same manner but different direction, as H’s in H2O are bent away the electrons on the O.
Sorry, for what I think Brother Adrian called, Illigitimus Parenthetica.
Electronegativity: O=3.44, Cl=3.16. As I understand, the chlorines will minimize repulsive forces by settling into the optimal angle from the oxygen. The Cl-Cl angles should be the same, and the Cl-O angle should be slightly larger than Cl-Cl. Exact numbers? Try scientific literature!