Cyclohexene is best prepared from cyclohexanol by which of the following

Options

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

Answer

A

Explanation

to suppress substitution and to favour elimination, the acid used must have a non-nucleophilic counter ion. The counter ion of HCl or HCl/`ZnCl_(2)` or HBr, i.e., `Cl^(-)` or `Br^(-)` ion is a strong nucleophile and hence forms either cyclohexyl chloride or cyclohexyl bromide by substitution reaction. in contrast, the counter ion of `H_(3)PO_(4)`, i.e., `PO_(4)^(3-)` is non-nucleophilic and hence does not give substitution product but gives only the elimination product, i.e., cyclohexene.