Question

When ethanol is heated with conc. H₂SO₄, a gas is produced. The compound formed, when this gas is treated with cold dilute aqueous solution of Baeyer’s reagent, is

• A. Formaldehyde
• B. Formic acid
• C. Glycol
• D. Ethanoic acid

Answer 1

The Correct Option is C

To solve this problem, we need to follow the reaction pathway of ethanol when heated with concentrated sulfuric acid (\(\text{H}_2\text{SO}_4\)). Here's a step-by-step breakdown: 

1. Dehydration of Ethanol: When ethanol (\(\text{C}_2\text{H}_5\text{OH}\)) is heated with concentrated \(\text{H}_2\text{SO}_4\), it undergoes a dehydration reaction to form ethene (\(\text{C}_2\text{H}_4\)), a gaseous product. The balanced chemical equation for this reaction is:

\(\text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{H}_2\text{SO}_4, \text{Heat}} \text{C}_2\text{H}_4 + \text{H}_2\text{O} \)

1. Treatment with Baeyer’s Reagent: Ethene (\(\text{C}_2\text{H}_4\)) is an unsaturated hydrocarbon and reacts with Baeyer's reagent (cold, dilute alkaline \(\text{KMnO}_4\)) to produce a diol. The reaction proceeds as follows:

\(\text{C}_2\text{H}_4 + \text{2[O]} \xrightarrow{\text{KMnO}_4} \text{C}_2\text{H}_4(\text{OH})_2 \)
 Here, glycol (ethylene glycol) is formed, which is a diol containing two \(\text{OH}\) groups.

1. Conclusion: Therefore, when the gas (ethene) produced from the initial reaction is treated with Baeyer's reagent, glycol (ethylene glycol) is formed. Thus, the correct answer is Glycol.

The other options can be ruled out as follows:

• Formaldehyde, Formic Acid, Ethanoic Acid: These compounds are not formed in the reaction sequence described. The specific oxidation of ethene by Baeyer's reagent yields glycol, not these compounds.

This problem illustrates a typical reaction of an alkene with an oxidizing agent, producing glycols by the syn-dihydroxylation of the alkene.

Answer 2