Problem 13 - Chemistry in 30 days

Question

An organic compound 'A', on oxidation, consumes one mole of periodic acid and yields one mole each of acetaldehyde and acetic acid. What would be the structure of ' \(A\) '? (a) \(\mathrm{CH}_{3} \mathrm{COCHOHCH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{COCOCH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CHOHCHOHCH}_{3}\) (d) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOHCHO}\)

Step-by-Step Solution

Answer

The structure of 'A' is (c) \(\mathrm{CH}_{3} \mathrm{CHOHCHOHCH}_{3}\).

Step 1: Understand the Reaction

The organic compound 'A' is oxidized to form acetaldehyde and acetic acid when it consumes one mole of periodic acid. Periodic acid cleaves vicinal diols, breaking the carbon-carbon bond between two alcohol groups.

Step 2: Recognize the Periodic Acid Reaction

The periodic acid reaction specifically targets vicinal diols, meaning two hydroxyl groups (-OH groups) attached to adjacent carbon atoms are required for it to work. The vicinal diol is cleaved into two separate carbonyl compounds.

Step 3: Analyze Given Options with Periodic Acid Cleavage

Option (c), \(\mathrm{CH}_{3} \mathrm{CHOHCHOHCH}_{3} \), contains a vicinal diol (two adjacent -OH groups). This compound will be cleaved by periodic acid to give acetaldehyde (\(\mathrm{CH}_{3}\mathrm{CHO}\)) and acetic acid (\(\mathrm{CH}_{3}\mathrm{COOH}\)).

Step 4: Confirm the Reaction Products

By cleaving the vicinal diol in option (c), the carbon chain is split between the two -OH groups. The left side of the chain (\(\mathrm{CH}_{3}\) group), forms acetaldehyde, and the right side with a methyl (\(\mathrm{CH}_{3}\)) and a carboxyl group (-COOH) forms acetic acid. This matches the products of the reaction given in the problem.

Key Concepts

Oxidation Reactions

In organic chemistry, oxidation reactions involve the increase in the oxidation state of a molecule. This often corresponds to the gain of oxygen, the loss of hydrogen, or the increase in the number of bonds to oxygen. For the compound 'A', the oxidation reaction requires periodic acid. This reagent, known for its oxidizing capability, specifically targets and cleaves vicinal diols—molecules with two hydroxyl groups on adjacent carbon atoms. As a result, these diols undergo oxidation, breaking down into smaller carbonyl compounds. Here, the products formed were acetaldehyde and acetic acid. These outcomes map directly onto the properties and function of periodic acid within oxidation reactions.

Vicinal Diols

Vicinal diols are molecules in which two hydroxyl groups (0H) are attached to adjacent carbon atoms in an organic compound. Due to their specific structure, these diols are especially reactive when exposed to certain oxidizing agents such as periodic acid. This reactivity is useful in synthetic organic chemistry, as it allows for the selective cleavage of carbon-carbon bonds adjacent to the hydroxyl groups. In the exercise, the diol structure of option (c), \(\mathrm{CH}_{3} \mathrm{CHOHCHOHCH}_{3} \), consists of exactly such a vicinal diol, making it a viable candidate for periodic acid oxidation. The reactivity and cleavage capability of vicinal diols in such reactions make them significant for understanding reaction mechanisms involving periodic acid.

Periodic Acid

Periodic acid, often represented as \(\mathrm{HIO}_4\), is a strong oxidizing agent used frequently in organic synthesis. Its primary utility lies in its ability to cleave vicinal diols. This characteristic is due to its capability to oxidize and break the carbon-carbon bonds between adjacent alcohols in these diols. The reaction typically yields two separate carbonyl compounds from a single vicinal diol. In the problem's context, periodic acid facilitates the transformation of the vicinal diol in the chosen compound structure into acetaldehyde and acetic acid. By understanding periodic acid's role in these reactions, chemists can effectively predict and manipulate the outcomes of oxidation processes in complex organic molecules.

Reaction Mechanisms

Reaction mechanisms in organic chemistry provide a step-by-step explanation of the transformations that occur during a chemical reaction. For the exercise, the periodic acid oxidation of vicinal diols involves several key steps:

• The periodic acid initially coordinates with the hydroxyl groups on adjacent carbons.
• This coordination facilitates the cleavage of the carbon-carbon bond connecting the diol.
• Once the bond is broken, each hydroxyl group is oxidized to form carbonyl groups—leading to separate aldehyde and carboxylic acid products.

By examining these steps, one can understand how the reaction progresses and why specific products are formed. Such mechanisms are crucial for anticipating the behavior of other similar reactions in organic chemistry.