Question

Lucas test is used for?
Options-
a.Alcohols
b.Amines
c.Diethyl ethers
d.Glacial acetic acid

Answer 1

Hint: Lucas test is mainly used for distinguishing between the different kinds of organic compounds containing a particular functional group with the help of a chemical reaction. Different kinds of the compound react with different rates that help us differentiate between them.

Complete answer:
Alcohol is a mildly acidic functional group that can be categorized into three different groups, the primary alcohol, secondary alcohol and tertiary alcohol.
If the hydroxyl group is attached to a carbon atom which only has a single carbon linked to it, then it is called a primary alcohol. If the hydroxyl group is attached to a carbon atom which is linked to two adjacent carbon atoms then it is called a secondary alcohol. If the hydroxyl group is attached to a carbon atom which is attached to three other carbon atoms directly then it’s called a tertiary alcohol.
The three types of alcohols can be distinguished on the basis of their reactivity towards different reagents. If the hydroxyl group needs to be substituted then primary alcohols show least reactivity and tertiary alcohols are the most reactive.
Lucas reagent is a mixture of hydrochloric acid along with zinc chloride that substitutes the hydroxyl group in alcohols with the chloride substituents.
The tertiary alcohols show turbidity immediately, the secondary alcohols show slow turbidity and primary alcohols do not show turbidity at all. This observation is in accordance with the reactivity trend of different alcohols.

\[ \Rightarrow \] Thus, Lucas test is used for alcohols and option (a) is correct.

Note:
The reason for tertiary alcohols being most reactive towards the Lucas reagent is that the hydroxyl group removal is accompanied by the formation of a carbocation intermediate which is stabilized by hyperconjugation. Primary carbocations are not that stable.