The best method to prepare cyclohexene form cyclohexanol is by using

Options

A. conc. `HCl`
B. `HBr`
C. Conc. `H_(3)PO_(4)`
D. Conc. `HCl + ZnCl_(2)`

Answer

C

Explanation

All the given reagents are acidic in nature. Thus, they provide proton to the alcohol to form protonated alcohol which then loses `H_(2)O` to form carbocation.

The resulting carbocation can erither lose a proton form adjacent carbon (elimination) to form an alkene or can under nucleophilic attack by conjugate base of acid to yield substitution product.
To get the best yield of alkene, we need to supress substitution but to favour elimination. this is possible when the conjugate base of acid used is non-nucleophilic in nature. the counter ions of `HCl, HCl//ZnCl_(2)` and `HBr` are `Cl^(-),Cl^(-)` and `Br^(-)` respecctively.