Question

The compound formed as a result of oxidation of ethyl benzene by \(\mathrm{KMnO}_{4}\) is (A) Benzophenone (B) Acetophenone (C) Benzoic acid (D) Benzyl alcohol

Short answer

The oxidation of ethyl benzene by KMnO4 involves the oxidation of the alpha-carbon of the ethyl group, converting it to a carbonyl group (C=O). The product formed is Acetophenone, which matches option (B). Therefore, the correct answer is (B) Acetophenone.

Step-by-step solution

Identify the oxidizable carbon

In ethyl benzene, the carbon of the ethyl group attached to the benzene ring are susceptible to oxidation. This carbon atom is called the alpha-carbon (the carbon attached directly to the benzene ring).

Understand the oxidation mechanism

KMnO4 will oxidize the alpha-carbon of the ethyl group, ultimately converting it to a carbonyl group (C=O). The alpha-hydrogen of the ethyl group is replaced with an oxygen atom.

Determine the oxidation product

After the alpha-carbon of the ethyl group is oxidized, the new compound will have a carbonyl group (C=O) attached to the benzene ring. This compound is called Acetophenone. The structure of Acetophenone is:  Now, let's match the oxidation product with the given options.

Match the product with the options

The oxidation product (Acetophenone) matches option (B). Hence, the correct answer is: (B) Acetophenone

Key concepts

Oxidation of Ethyl Benzene

Understanding the oxidation of ethyl benzene is crucial for students studying organic chemistry, especially when preparing for competitive exams like JEE Main and Advanced. Ethyl benzene, consisting of an ethyl group attached to a benzene ring, undergoes oxidation when treated with a strong oxidizing agent such as potassium permanganate (KMnO_4).

In the oxidation process, the alpha-carbon— the carbon atom directly attached to the benzene ring— is targeted. The presence of at least one hydrogen atom on this carbon is essential for the oxidation to proceed. When KMnO_4 is introduced, it effectively removes these hydrogen atoms to form a carbonyl group (C=O), transforming the ethyl group into an acetyl group.

Through this mechanism, ethyl benzene is converted to acetophenone, characterized by the introduction of a carbonyl function at the alpha position. This understanding helps students identify acetophenone, with its distinctive chemical structure, as the product of ethyl benzene oxidation in the given problem.

Oxidation Product Analysis

• Ethyl group (CH_3CH_2-) is oxidized to an acetyl group (CH_3C(=O)-).
• The hydrogen atoms on the alpha-carbon are replaced by an oxygen atom.
• The resultant carbonyl compound is acetophenone with a ketone functional group.

KMnO4 Reaction Mechanism

Potassium permanganate (KMnO_4) is recognized for its strong oxidizing power in organic chemistry and is widely used in various oxidation reactions. The KMnO_4 reaction mechanism is a process where the Mn(VII) ion is reduced, while the organic compound is oxidized. This happens through a radical and a non-radical pathway, depending on the conditions, such as pH and temperature.

In acidic conditions, KMnO_4 can even cleave carbon-carbon bonds, but in the case of ethyl benzene, it specifically oxidizes the alpha-carbon as discussed in the previous section. The MnO_4^- ions gain electrons and are reduced, eventually turning into Mn^{2+} ions, while the organic compound loses hydrogen atoms and gains an oxygen, manifesting in the formation of a carbonyl group.

Key Aspects of the KMnO_4 Reaction

• KMnO_4 acts as an oxidizing agent and is reduced in the process.
• The reaction typically requires acidic conditions and heat.
• MnO_4^- is the reactive species that accepts electrons and gets reduced.
• The organic substrate, in turn, is oxidized, often forming carbonyl compounds or carboxylic acids.

Identification of Organic Compounds

The identification of organic compounds is a fundamental aspect of organic chemistry. It involves determining the structure or functional groups present in a compound based on its chemical properties and reactions. Techniques such as spectroscopy (NMR, IR, UV-Vis), chromatography, and classical wet chemical tests are used for identification.

In educational contexts, like JEE exam preparation, students often identify organic compounds by logical deduction from chemical reactions or characteristic functional group tests. For example, in the oxidation of ethyl benzene, knowing the reactivity of KMnO_4 allows us to predict the formation of a carbonyl compound. The presence of a ketone functional group in acetophenone can further be confirmed by tests like 2,4-dinitrophenylhydrazine (DNPH) test, which would result in a yellow or orange precipitate, indicative of a ketone or aldehyde group.

Techniques for Identification

• Spectroscopy provides information about molecular structure.
• Chromatography separates compounds based on their physical properties.
• Chemical tests reveal the presence of specific functional groups.

By incorporating these techniques, students can elucidate the structure of unknown organic compounds, sharpening their analytical and deductive skills prevalent in organic chemistry problem-solving.