Phenol

Why the yield of chlorobenzene is generally poor, When phenol is treated with PCl5 ???

5 Answers

21
Anirban Mukherjee ·

C6H5OH + PCl5→ C6H5Cl + POCl3 + HCl
3 C6H5OH + POCl3 → (C6H5)3PO4 + 3 HCl

The POCl3 formed in the first step consumes the phenol further by 3 moles to give mainly triphenyl phosphate.Thus if we use 4 moles of phenol we get only 1 mole of chlorobenzene just because of the POCl3 formed in the first step!

383
Soumyabrata Mondal ·

please show me the mechanism.

21
Anirban Mukherjee ·

The O-C bond in phenol acquires a double bond character due to resonance and so it is difficult to break that bond to substitute -Cl.

383
Soumyabrata Mondal ·

If the O-C bond in phenol acquires a double bond, then O can release Hydrogen and O-H bond pair electrons can be contributed for making O=C bond. And Cl can form bond with H to produce HCl.

Is there any confusion!!............

21
Anirban Mukherjee ·

The l.p of electrons on the oxygen atom contributes for the partial double bond character of the O-C bond

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