Question

Cyclohexene is best prepared from cyclohexanol by which of the following reagents:

• A. conc. $H_{3}P{O}_4$
• B. conc. $HCl/ZnC{l}_2$
• C. conc. $HCl$
• D. conc. $HBr$

Answer 1

The correct option is A conc. $H_{3}P{O}_4$

From the given options, $conc.H_{3}P{O}_4$ is the only dehydrating agent.

Thus, cyclohexanol will undergo dehydration to form cyclohexene through carbocation intermediate.
In step 1, the $OH$ will abstract the $H^{+}$ from acid and removes as $H_{2}O$ molecule.
In step 2, the hydrogen is eliminated to form alkene product.