Question

The reaction $ \left [ CH_3-C \left ( CH_3 \right ) OH-CH_3+ \ \ \ H_2SO_4\ \ \rightarrow CH_3-CCH_3=CH_2 \right ]$ is the example of
A. Sulphonation
B. Dehydration
C. Alkylation
D. Decomposition

Answer 1

Hint: H₂SO₄ is a good dehydrating agent. It absorbs the H₂O from the compounds. Sulphuric acid is also a strong oxidising agent thus it removes oxygen from the compounds. For dehydration of alcohol, the acids that are used are concentrated sulphuric acid or concentrated phosphoric acid.

Complete Step by Step Answer:
In the given reaction H₂SO₄ is used as a catalyst and H₂SO₄ has a strong attraction toward water. Sulphuric acid is a strong oxidising agent. Sulphuric acid is hydrophilic, meaning water loving.

Alcohol reacts with sulphuric acid and produces alkene and water. It is an E1 elimination process. For E1 elimination a good living group must be attached to the substrate and OH is a good living group in a polar protic solvent. For elimination reaction higher temperature is required. In E1 saytzeff alkene will be formed.

In the given reaction:
$CH_3-CCH_3OH-CH_3 \ + \ \ H_2SO_4\ \ \rightarrow CH_3-CCH_3=CH_2 + H_2O$
The mechanism of reaction is:
$CH_3-CCH_3OH-CH_3 + \ \ \ H_2SO_4/H^+ \ \ \rightarrow CH_3-CCH_3{OH_2}^+-CH_3 \rightarrow \ \ -H_2O \ \ CH_3-C^+CH_3-CH_3 \rightarrow \ \ -H^+\ \ CH_3-CCH_3=CH_2$

In the given reaction protonation takes place at OH and OH removes as H₂O in the reaction then carbocation is formed which further releases H⁺ ion in the reaction producing alkene as the product. In the reaction formation of carbocation is a slow step hence if the living group again gets attached to the carbocation we will get the starting material back. His reaction is a unimolecular reaction.
Thus, Option (A) is correct

Note: Sulphuric acid is used in the desiccator, desiccator is a completely sealed container which is used to remove moisture/water content from the compounds or substances. Desiccator is mostly used in chemical laboratories. Desiccator is sealed using lubricant like grease.