Question

Which of the following reagents could be used to distinguish between hexan-1-ol and cyclohexanol?

• A. Lucas reagent
• B. $ZnC{l}_{2}andHCl$
• C. A Cr(VI) reagent like $H_{2}Cr{O}_4$
• D. Bromine water

Answer 1

Answer: (A), (B)

$ZnC{l}_{2}andHCl$

In other words, distinguish between a primary alcohol and a secondary alcohol. Using a Chromium VI compound can oxidize
primary alcohols and secondary alcohols and in the process, the reagent loses its orange colour. Hence $H_{2}Cr{O}_4$ can’t be used.

For a positive Lucas test, primary alcohols take a long time – more than 5 minutes, whereas secondary alcohols react more quickly.
The time difference can help identify which is which. And don’t forget, Lucas reagent is $ZnC{l}_{2}andHCl$.