Question

Butyne on reaction with hot alkaline \(\mathrm{KMnO}_{4}\) gives (1) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH}\) (2) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}\) (3) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}+\mathrm{CO}_{2}\) (4) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}+\mathrm{HCOOH}\)

Short answer

The correct product is \(\mathrm{CH_3CH_2COOH + HCOOH}\) which corresponds to option (4).

Step-by-step solution

Identify the reagents and reactants

The reactant in the given problem is Butyne, and the reagent is hot alkaline \(\mathrm{KMnO}_{4}\). This is an oxidative cleavage reaction of an alkyne.

Determine the structure of Butyne

Butyne can be either 1-butyne (\(\mathrm{CH_3-CH_2-C\equiv CH}\)) or 2-butyne (\(\mathrm{ CH_3-C\equiv C-CH_3}\)).

Recall the product of alkyne with hot alkaline \(\mathrm{KMnO}_{4}\)

Under these conditions, the alkyne breaks at the triple bond, and each of the carbon atoms involved in the triple bond transforms into a carboxyl group (\(\mathrm{-COOH}\)).

Apply oxidative cleavage to Butyne

Consider both possible forms of Butyne (1-butyne and 2-butyne):For 1-butyne: \(\mathrm{CH_3-CH_2-C\equiv CH} \rightarrow \mathrm{CH_3-CH_2-COOH + HCOOH}\)For 2-butyne: \(\mathrm{CH_3-C\equiv C-CH_3} \rightarrow \mathrm{2CH_3-COOH}\)

Compare with given options

Compare the predicted products against the given choices. The oxidation of 1-butyne yields \(\mathrm{CH_3CH_2COOH + HCOOH}\), which matches choice (4).

Key concepts

alkyne oxidative cleavage

Oxidative cleavage is a type of organic reaction where a carbon-carbon multiple bond, such as a double or triple bond, is broken, leading to the formation of two or more simpler molecules. This reaction is commonly used to understand the structure of complex molecules by breaking them down into more manageable fragments. When it comes to alkynes, which have carbon-carbon triple bonds, the oxidative cleavage is uniquely significant due to the reactivity and potential products formed. When an alkyne undergoes oxidative cleavage, the triple bond is split, and each carbon atom that was part of the triple bond is converted into a carboxyl group (\(\text{-COOH}\)) or other forms depending on the specific reagents used.

potassium permanganate reaction

Potassium permanganate (KMnO4) is a powerful oxidizing agent that is often used in organic chemistry to induce oxidative reactions. This reagent is particularly efficient in breaking down multiple bonds in organic molecules. In the case of alkynes, hot alkaline KMnO4 facilitates the cleavage of the triple bond, resulting in the formation of carboxylic acids. The reaction typically requires heating and an alkaline environment to proceed effectively. Here’s a simplified outline of how potassium permanganate reacts:

• Hot alkaline KMnO4 attacks the carbon-carbon triple bond of the alkyne.
• The triple bonds break, and each carbon becomes bonded to an oxygen atom.
• The newly formed groups convert into carboxylic acids given the conditions.

In the provided exercise, Butyne reacts with hot alkaline KMnO4, leading to the oxidative cleavage of the triple bond, and yields different carboxylic acids depending on the structure of Butyne (whether it’s 1-butyne or 2-butyne). For example, 1-butyne yields acetic acid and formic acid (CH3CH2COOH + HCOOH), which matches the answer choice (4) in the given multiple-choice options.

organic reaction mechanisms

Organic reaction mechanisms provide a step-by-step description of how a particular reaction takes place. Understanding these mechanisms can deeply enhance your grasp of organic chemistry by illustrating how the atoms and molecules interact and change during the reaction. Reactions involving alkynes, such as the oxidative cleavage described above, follow specific steps:

• Initial Attack: The nucleophilic or electrophilic attack initiates the reaction.
• Bond Breaking: Critical bonds, such as the triple bonds in alkynes, are broken.
• Intermediate Formation: Various intermediates, like carbonyl or carboxylic acid groups, are formed.
• Final Product Formation: The intermediates reorganize or are further reacted to yield the final products.

This step-by-step understanding helps predict the outcome of reactions and explain why certain products are formed, such as why 1-butyne reacts with KMnO4 to form acetic acid and formic acid. By familiarizing yourself with these mechanisms, you can better navigate organic chemistry problems and approach new reactions with confidence.