Question

Which of the following statement is not correct? (1) Acidified \(\mathrm{KMnO}_{4}\) or \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) oxidises alkenes to carbonyl compounds finally to carboxylic acids (2) Terminal alkenes give \(\mathrm{CO}_{2}\) as one of the product when oxidised with acidified \(\mathrm{KMnO}_{4}\) or \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (3) Acidified \(\mathrm{KMnO}_{4}\) or \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) oxidises 2 -butene to acetic acid but 2,3 -dimethyl-2-butene to acetone (4) Oxidation of 2-methyl propene with acidified \(\mathrm{KMnO}_{4}\) or \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) gives acetone and formaldehyde

Short answer

Statement 4 is not correct.

Step-by-step solution

Understand the Reaction Mechanism

Acidified \(\text{KMnO}_4\) or \(\text{K}_2 \text{Cr}_2 \text{O}_7\) are strong oxidizing agents that can convert alkenes to carbonyl compounds and further oxidize them to carboxylic acids.

Analyze Statement 1

Statement 1 correctly states that acidified \(\text{KMnO}_4\) or \(\text{K}_2 \text{Cr}_2 \text{O}_7\) oxidizes alkenes to carbonyl compounds and further to carboxylic acids. This statement is correct.

Analyze Statement 2

Terminal alkenes produce \(\text{CO}_2\) as a product when oxidized with strong oxidizing agents like acidified \(\text{KMnO}_4\) or \(\text{K}_2 \text{Cr}_2 \text{O}_7\). This statement is correct.

Analyze Statement 3

2-butene can indeed be oxidized to acetic acid (\text{CH}_3 \text{COOH}) with acidified \(\text{KMnO}_4\) or \(\text{K}_2 \text{Cr}_2 \text{O}_7\). However, 2,3-dimethyl-2-butene when oxidized forms acetone (\text{CH}_3 \text{COCH}_3), so this statement is correct as well.

Analyze Statement 4

2-methylpropene when oxidized with acidified \(\text{KMnO}_4\) or \(\text{K}_2 \text{Cr}_2 \text{O}_7\) does not produce acetone and formaldehyde. Instead, it produces acetic acid and formic acid. Hence, this statement is not correct.

Key concepts

oxidizing agents

Oxidizing agents are substances that can accept electrons from other substances during a chemical reaction. This process is called oxidation.
In the context of alkenes, strong oxidizing agents like potassium permanganate \(\text{KMnO}_4\) and potassium dichromate \(\text{K}_2 \text{Cr}_2 \text{O}_7\) play a critical role. These agents help transform alkenes into different compounds. Here’s what happens:
\(\text{KMnO}_4\) and \(\text{K}_2 \text{Cr}_2 \text{O}_7\) are mixed with an acid, such as sulfuric acid, to create acidified solutions. When these solutions react with alkenes:

• Step 1: The alkene is converted into carbonyl compounds (like aldehydes and ketones).
• Step 2: These carbonyl compounds can be further oxidized to form carboxylic acids.

Recognizing these transformations is crucial for understanding the behavior and potential products.

reaction mechanism

A reaction mechanism explains step-by-step how a chemical reaction occurs at the molecular level.
For the oxidation of alkenes using strong oxidizing agents like \(\text{KMnO}_4\) or \(\text{K}_2 \text{Cr}_2 \text{O}_7\), the mechanism is fairly straightforward. Here's a simple breakdown:

• The double bond present in alkenes opens up to form a cyclic intermediate with \(\text{KMnO}_4\) or \(\text{K}_2 \text{Cr}_2 \text{O}_7\).
• Water molecules from the reaction mixture help cleave the intermediate cyclic compound.
• This cleavage results in the formation of diols (compounds with two hydroxyl groups).
• Further oxidation of these diols occurs, leading to the formation of carbonyl compounds (aldehydes or ketones).
• Finally, these carbonyl compounds can be further oxidized to yield carboxylic acids.

Understanding the mechanism will help you predict the final products of these oxidation reactions.

chemical reactions

Chemical reactions involving alkenes and oxidizing agents often result in the formation of multiple products.
Let's illustrate this with specific examples:

• Example 1: Oxidation of 2-butene with acidified \(\text{KMnO}_4\) or \(\text{K}_2 \text{Cr}_2 \text{O}_7\) yields acetic acid. The reaction breaks the double bond and converts it into carboxylic acid.
• Example 2: 2,3-dimethyl-2-butene, when oxidized with these agents, forms acetone. Here, the bulky groups surrounding the double bond limit further oxidation to carboxylic acids.
• Example 3: 2-methylpropene, under the same conditions, produces not acetone and formaldehyde as one might expect, but acetic acid and formic acid instead. This shows that proper understanding and prediction of products require familiarity with the specific reaction mechanisms.

Analyzing chemical reactions and their outcomes enables you to grasp how different reagents and conditions can alter the final products.