Question

An organic compound \( A \), molecular formula \( C_2H_6O \), oxidises with \( Cr_2O_7 \) to form a compound \( B \). Compound \( B \) on warming with iodine and aqueous solution of NaOH gives a yellow precipitate of compound \( C \). When compound \( A \) is heated with conc. \( H_2SO_4 \) at 413 K, it gives a compound \( D \), which on reaction with excess HI gives compound \( E \). Identify compounds \( A \), \( B \), \( C \), \( D \), and \( E \) and write chemical equations involved.

Hint:

The iodoform test (formation of yellow precipitate) is used to detect compounds with a structure \( CH_3CO \) or \( CH_3CH \), such as aldehydes and alcohols.

Answer 1

Compound \( A \) has the molecular formula \( C_2H_6O \), which suggests it is ethanol.
When ethanol is oxidized by \( Cr_2O_7 \), it forms acetic acid, \( CH_3COOH \), which is compound \( B \).
When acetic acid reacts with iodine and NaOH, it forms a yellow precipitate of iodoform (\( CHI_3 \)), which is compound \( C \).
When ethanol is heated with conc. \( H_2SO_4 \) at 413 K, it undergoes dehydration to form ethene (\( C_2H_4 \)), which is compound \( D \).
When ethene reacts with excess HI, it forms iodoethane (\( C_2H_5I \)), which is compound \( E \).
The chemical equations involved are as follows:
1. \( C_2H_5OH + Cr_2O_7^{2-} \to CH_3COOH \)
2. \( CH_3COOH + I_2 + NaOH \to CHI_3 \) (yellow precipitate)
3. \( C_2H_5OH \xrightarrow{H_2SO_4, 413K} C_2H_4 + H_2O \)
4. \( C_2H_4 + I_2 \to C_2H_5I \)