Question

2 -phenyl ethanol on oxidation with alkaline \(\mathrm{KMnO}_{4}\) gives (a) benzaldehyde (b) 2 -phenyl ethanoic acid (c) benzoic acid (d) 2 -phenyl ethanol

Short answer

Answer: 2-phenyl ethanoic acid

Step-by-step solution

Identify the reactant and the oxidizing agent

The reactant is 2-phenyl ethanol, which is a primary alcohol with a phenyl group attached. The oxidizing agent is alkaline \(\mathrm{KMnO}_{4}\) (potassium permanganate in alkaline conditions).

Determine the oxidation state of the carbon atom to be oxidized

In 2-phenyl ethanol, the alcohol group has a carbon atom adjacent to the phenyl group. The oxidation state of this carbon atom can be found using the formula: x + (-2)(Number of O atoms) + (Number of H atoms) = 0. In this case, x + (-2)(1) + (1) = 0, leading to x = 1. Therefore, the carbon atom to be oxidized has an oxidation state of +1.

Determine the possible products of the oxidation reaction

There are two possible products after the oxidation of a primary alcohol: an aldehyde and a carboxylic acid. The correct product will depend on the type of oxidizing agent used. Alkaline \(\mathrm{KMnO}_{4}\) is a strong oxidizing agent, which will oxidize primary alcohols to carboxylic acids.

Identify the correct carboxylic acid product

From the given options, the carboxylic acid that could be formed by the oxidation of 2-phenyl ethanol is 2-phenyl ethanoic acid (option b). To conclude:

State the correct answer

2-phenyl ethanol on oxidation with alkaline \(\mathrm{KMnO}_{4}\) gives 2-phenyl ethanoic acid (option b).

Key concepts

Oxidation Reactions

In organic chemistry, oxidation reactions involve the process where an organic molecule gains oxygen or loses hydrogen atoms. Typically, this process results in an increase in the oxidation state of a carbon atom. Oxidation reactions are crucial for transforming different organic compounds.

• They are essential in forming bonds with oxygen, leading to new functional groups being created.
• In the context of alcohols, oxidation results in the conversion of alcohols to aldehydes or carboxylic acids.

For primary alcohols, the oxidation process involves the removal of hydrogen atoms and the addition of one or more oxygen atoms, depending on the strength and type of oxidizing agent used.

Alkaline KMnO4

Alkaline potassium permanganate, represented as \(\mathrm{KMnO}_{4}\), is a powerful oxidizing agent commonly used in organic chemistry to carry out oxidation reactions. It is particularly renowned for its ability to oxidize primary alcohols into carboxylic acids.

• The solution is typically alkaline (basic) due to the addition of a base like sodium hydroxide, \(\mathrm{NaOH}\).
• In an alkaline medium, KMnO4 facilitates intense oxidation conditions that can push primary alcohols beyond the aldehyde stage to full conversion into carboxylic acids.

It serves as a reliable choice when complete oxidation is desired, making it a staple in organic synthesis where robust and efficient oxidation is sought.

Primary Alcohols

Primary alcohols are organic compounds that contain an -OH group (hydroxyl group) bonded to a carbon atom that is attached to only one other carbon atom. This structural characteristic defines their position as primary alcohols.
Examples include:

• Methanol (\(\mathrm{CH_3OH}\))
• Ethanol (\(\mathrm{C_2H_5OH}\))
• 2-Phenyl ethanol

In oxidation reactions, primary alcohols initially get oxidized to aldehydes. With strong oxidizing agents like alkaline \(\mathrm{KMnO_4}\), they further oxidize to carboxylic acids, which contain a carbonyl and hydroxyl group attached to the same carbon, resulting in an increased oxidation state for the carbon atom.

Carboxylic Acids

Carboxylic acids are organic compounds that contain a carboxyl group \((\mathrm{-COOH})\). They are characterized by their acidic properties, as the hydrogen in the hydroxyl group is weakly bound and can be released as a proton (H+).

• These compounds are typically formed through the complete oxidation of primary alcohols.
• They are widely used and are integral in the manufacture of polymers, pharmaceuticals, and other chemical synthesis processes.

During the oxidation of a primary alcohol with alkaline \(\mathrm{KMnO_4}\), a carboxylic acid like 2-phenyl ethanoic acid can be formed. This process effectively makes use of the strong oxidative ability of alkaline KMnO4, linking alcohol oxidation directly to carboxylic acid synthesis.