Reaction Mechanism

The reaction shown is a free radical halogenation reaction. This method is unsuitable for the preparation of fluoroarenes because of the high reactivity of fluorine. Fluorine is so reactive that it is difficult to control the reaction, leading to multiple substitutions. In this reaction, the free radical is formed by using the metal Fe in dark conditions. For the other halogens, the reaction can be controlled to obtain the corresponding haloarenes.

Let’s trace the reaction sequence
Step 1: (methanol) reacts with thionyl chloride to form chloromethane (A):

Step 2: reacts with potassium cyanide (KCN) in aqueous ethanol to form acetonitrile (B):

Step 3: Acetonitrile (B) is reduced using sodium amalgam in ethanol to form ethylamine (C):

Step 4: Ethylamine (C) undergoes diazotization with sodium nitrite and hydrochloric acid , followed by hydrolysis with water to produce ethanol (D) as the major product:

Conclusion: The major product D is ethanol

Let’s analyze each reaction:
1. Reaction (1):

This reaction shows the hydrolysis of an acyl chloride (acetyl chloride) to a carboxylic acid (acetic acid). This is a standard reaction. Acyl chlorides readily react with water to form carboxylic acids.
2. Reaction (2):

This reaction depicts the attempted reduction of benzamide to benzoic acid using lithium aluminum hydride (LiAlH₄). This is incorrect. LiAlH₄ is a strong reducing agent that reduces amides to amines, not carboxylic acids. The correct product would be benzylamine.

3. Reaction (3):

This reaction shows the oxidation of ethanol to acetic acid using alkaline potassium permanganate (KMnO₄), followed by acidification. This is a standard oxidation reaction.
4. Reaction (4):

This reaction shows the oxidation of propanol to propanoic acid using a mixture of chromium trioxide (CrO₃) and sulfuric acid (H₂SO₄). This is also a standard oxidation reaction.

This reaction sequence involves a series of transformations:

1. Chlorination: Chlorination of the ethylbenzene ring will occur preferentially at the para position due to the activating effect of the ethyl group and the deactivating meta-directing nature of the nitro group.
2. Reduction: Reduction of the nitro group (-NO₂) to an amino group (-NH₂) using tin and hydrochloric acid (Sn/HCl).
3. Diazotization: The amino group is converted into a diazonium group (-N₂⁺) using sodium nitrite and hydrochloric acid (NaNO₂/HCl) at a low temperature (273-278 K).
4. Sandmeyer Reaction: The diazonium group is replaced by an iodide (I) using potassium iodide (KI) via a Sandmeyer reaction. This replacement occurs at the same position as the original amino group (and thus the nitro group).
   Thus, we have 4-iodo-1-ethyl-2-chlorobenzene.

Baeyer's reagent is a cold, dilute, alkaline solution of potassium permanganate KMnO₄.
It is a powerful oxidizing agent and is used as a test for unsaturation (presence of double or triple bonds) in organic compounds. The permanganate ion MnO₄^- is a deep purple color.
When it reacts with an unsaturated compound, the purple color disappears, and a brown precipitate of manganese dioxide MnO₂ forms. This decolorization of the permanganate solution is a positive test for unsaturation. It's important that the solution be cold and dilute; otherwise, the reaction may proceed too vigorously, and the permanganate may oxidize the organic compound further.