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PCl_(5) reactws with ethanol to form chloroethane. However, with phenol, it does not give chlorobenzene but gives triphenylphoshate. Explain. |
Answer» SOLUTION :To begin with both ethanol and phenol react with `PCl_(5)` to give the corresponding chlorophosphate ESTERS.  Since in ethanol, C-O bond has only single bond CHARACTER, therefore, nucleophilic ATTACK by `Cl^(-)` ion occurs easily on chlorophosphate ester (I) to give chloroethane.  however, in case of phenol, C-O bond has some double bond character due to resonance and hence difficult to break. instead nucleophilic attack by `C_(6)H_(5)OH` occurs twice on the chlorophosphate ester (II) to form intermediate (III). further, nucleophilic attack by `C_(6)H_(5)OH` on III does not occur due to steric hindrance. Instead (III) undergoes hydrolysis by water to form triphenylphosphate.  .
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