Question

The alcohol that reacts faster with Lucas reagent is?
  a.)$\text{C}{{\text{H}}_{\text{3}}}-\text{C}{{\text{H}}_{\text{2}}}-\text{C}{{\text{H}}_{\text{2}}}-\text{C}{{\text{H}}_{\text{2}}}-\text{OH}$

b.) $\begin{align} & \text{C}{{\text{H}}_{\text{3}}}-\text{C}{{\text{H}}_{\text{2}}}-\text{CH}-\text{C}{{\text{H}}_{\text{3}}} \\ & \text{ }\!\!|\!\!\text{ } \\ & \text{ OH} \\ \end{align}$

  c.)$\begin{align}&\text{C}{{\text{H}}_{\text{3}}}-\text{C}{{\text{H}}_{{}}}-\text{C}{{\text{H}}_{2}}-\text{OH} \\ & \text{ }\!\!|\!\!\text{ } \\ & \text{ C}{{\text{H}}_{\text{3}}} \\ \end{align}$

d.) $\begin{align}& \text{ C}{{\text{H}}_{3}}\text{ } \\ & \text{ }\!\!|\!\!\text{ } \\ & \text{C}{{\text{H}}_{\text{3}}}-\text{ C}-\text{OH} \\ & \text{ }\!\!|\!\!\text{ } \\ & \text{ C}{{\text{H}}_{\text{3}}} \\ \end{align}$

Answer 1

Hint: We know that Lucas test of alcohols is done with the following reaction:
$\text{R}-\text{OH }+\text{ HCl }\xrightarrow{\text{Anhydrous ZnC}{{\text{l}}_{\text{2}}}}\text{ RCl + }{{\text{H}}_{\text{2}}}\text{O}$
Using this reaction we will be able to determine which alcohol reacts faster with the Lucas test. We need to know the structure of the alcohol as well.
Step by Step answer:
The alcohol that reacts with Lucas agent faster is 2-methylpropan-2-ol which has a molecular structure of:
$\begin{align}
  & \text{ C}{{\text{H}}_{3}}\text{ } \\
 & \text{ }\!\!|\!\!\text{ } \\
 & \text{C}{{\text{H}}_{\text{3}}}-\text{ C}-\text{OH} \\
 & \text{ }\!\!|\!\!\text{ } \\
 & \text{ C}{{\text{H}}_{\text{3}}} \\
\end{align}$
It is a tertiary alcohol. The product of this reaction is 2-chloro-2-methylpropane.
$\text{1}{}^\circ $ Alcohol reacts very slowly with Lucas reagent on heating.
$2{}^\circ $ Alcohol reacts with Lucas reagent much faster than $\text{1}{}^\circ $ alcohol.
$3{}^\circ $ Alcohol reacts immediately at room temperature when reacted with Lucas reagent.
A mixture of HCl and anhydrous zinc chloride is called Lucas reagent.
Therefore the correct answer is Option D.
Note: We know that Lucas reagent is a solution of anhydrous zinc chloride in concentrated hydrochloric acid solution. It is used to classify alcohols of low molecular weight; the reaction is a substitution in which the chlorine replaces the hydroxyl group.
The main function of Lucas test is used to differentiate and categorise primary, secondary and tertiary alcohol.
There is an interesting fact about the Lucas reagent that is primary alcohol does not react with Lucas reagent at room temperature. This is because the negative charge of our group is stabilized more by an alpha carbon rather than hydrogen attached to the carbon.