Question

Which of the following on oxidation followed by hydrolysis gives pyruvic acid? (a) acetone cyanohydrin (b) acetaldehyde cyanohydrin (c) formaldehyde cyanohydrin (d) none of these

Short answer

(b) Acetaldehyde cyanohydrin

Step-by-step solution

Understanding the Compounds

First we need to understand that a cyanohydrin is a molecule containing a nitrile (CN) group and a hydroxyl (OH) group connected to the same carbon, derived from an aldehyde or ketone. Acetone and cyanide form acetone cyanohydrin, acetaldehyde and cyanide form acetaldehyde cyanohydrin, and formaldehyde and cyanide form formaldehyde cyanohydrin.

Analyzing the Oxidation Process

In oxidation, the nitrile group in a cyanohydrin is converted into a carboxylic acid group. For example, when acetone cyanohydrin undergoes oxidation, ideally, as it consists of a ketone-derived cyanohydrin, it might not form a carboxylic acid directly like pyruvic acid. However, acetaldehyde cyanohydrin undergoing oxidation converts the nitrile group into a carboxyl group, forming an alpha-keto acid.

Identifying Hydrolysis Reaction

Hydrolysis of the oxidized compound turns the nitrile into a carboxylic acid. In acetaldehyde cyanohydrin, the hydrolysis leads to forming a 2-oxo acid, specifically pyruvic acid, showing that only acetaldehyde cyanohydrin will yield pyruvic acid after this process.

Conclusion on Correct Option

Synthesizing the above, acetaldehyde cyanohydrin is the initial reactant that, when oxidized, converts the nitrile group into a carboxylic acid and upon hydrolysis produces pyruvic acid. Acetone and formaldehyde cyanohydrin don't form pyruvic acid after these reactions.

Key concepts

Oxidation

Oxidation is a fundamental reaction in chemistry that involves the loss of electrons from a molecule. In the context of organic chemistry, and particularly with cyanohydrins, oxidation often results in the transformation of functional groups. When a cyanohydrin undergoes oxidation, its nitrile group can be converted into a carboxylic acid group. This conversion is essential for the formation of certain key compounds.

In the exercise, acetaldehyde cyanohydrin undergoes oxidation, leading to the conversion of its nitrile group into a carboxyl group, which is one step towards forming pyruvic acid. This example shows how oxidation can lead to significant structural changes in molecules, allowing for the synthesis of complex organic compounds.

Hydrolysis

Hydrolysis is a chemical reaction in which a molecule reacts with water, leading to the breakdown of that molecule. In the case of cyanohydrins, hydrolysis is an essential step after oxidation. It leads to the transformation of nitrile groups into carboxylic acids.

The hydrolysis of oxidized acetaldehyde cyanohydrin specifically results in the formation of pyruvic acid. This shows how hydrolysis works in tandem with oxidation to complete the conversion of substances into desired compounds. It's a classic example of how multiple chemical reactions work together in organic chemistry to create specific results.

Cyanohydrins

Cyanohydrins are a fascinating group of organic compounds that contain both a nitrile (\( \text{CN} \)) and a hydroxyl (\( \text{OH} \)) group attached to the same carbon atom. They are typically derived from reactions involving aldehydes or ketones and hydrogen cyanide.

In the given problem, cyanohydrins act as the starting material. Each type of cyanohydrin correlates with its parent aldehyde or ketone: for acetone cyanohydrin, acetone is the start; for acetaldehyde cyanohydrin, it is acetaldehyde. The cyanohydrin's structure plays a critical role in determining the compound it can form when further chemical processes, like oxidation and hydrolysis, are applied.

Pyruvic Acid

Pyruvic acid is a key organic compound that plays a vital role in cellular respiration. Structurally, it's known as a 2-oxo acid, with the formula \( \text{C}_3\text{H}_4\text{O}_3 \). Its formation through chemical processes, such as oxidation and hydrolysis, makes it an interesting target in synthetic chemistry.

In this problem, pyruvic acid is the final product after the oxidation and hydrolysis of acetaldehyde cyanohydrin. The specific structure of pyruvic acid, which includes both a carboxylic acid and a ketone group, is indicative of its origins from acetaldehyde cyanohydrin, showing its unique status and importance in both chemistry and biology.

Nitrile Group

The nitrile group, symbolized as \( \text{CN} \), is a functional group in organic chemistry that features a carbon triple-bonded to a nitrogen. This group is pivotal in many synthetic pathways, including the conversion of cyanohydrins.

In the oxidation process described in the original exercise, the nitrile group of acetaldehyde cyanohydrin is converted to a carboxylic acid group. This transformation is crucial, as it is a key step in forming pyruvic acid. Understanding the reactivity of the nitrile group helps in predicting and manipulating reactions in organic synthesis.

Carboxylic Acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group (\( \text{COOH} \)). They are found ubiquitously in nature and are prominent in various chemical reactions and synthesis processes.

The conversion of the nitrile group of acetaldehyde cyanohydrin to a carboxylic acid is an essential part of forming pyruvic acid. Carboxylic acids like pyruvic acid, being versatile intermediates, highlight the importance of such transformations in crafting more complex organic molecules. This specific conversion underscores the broader utility of carboxylic acids in industrial applications and biochemical processes.