Problem 173 - A Complete Resource Book in Chemistry for JEE Main

Question

On warming with \(\mathrm{I}_{2}\) and aqueous \(\mathrm{NaOH}\), iodoform and sodium succinate are formed. The formula of the compound should be (a) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{COC}_{6} \mathrm{H}_{s}\) (c) \(\mathrm{CH}_{3}^{3}-\mathrm{CO}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{COOH}\) (d) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{COCH}_{3}\)

Step-by-Step Solution

Answer

The correct formula is option (c) \(\mathrm{CH_{3}COCH_{2}CH_{2}COOH}\).

Step 1: Understand Iodoform Reaction

The iodoform reaction is a chemical test that is used to determine the presence of a methyl ketone group, specifically compounds containing the group \(\mathrm{CH_3CO} \). This reaction works best on methyl ketones, acetaldehyde, ethanol, or other alcohols that can be oxidized to methyl ketones.

Step 2: Analyze Given Options for Methyl Ketone

We need to identify which of the given options have a methyl ketone group (\(\mathrm{CH_3CO}\)) that would result in the iodoform reaction and give iodoform (\(\mathrm{CHI_3}\)). List of options:- (a) \(\mathrm{CH_{3}COCH_{2}CH_{2}CH_{3}}\)- (b) \(\mathrm{CH_{3}COC_{6}H_{5}}\)- (c) \(\mathrm{CH_{3}COCH_{2}CH_{2}COOH}\)- (d) \(\mathrm{CH_{3}COCH_{2}CH_{2}COCH_{3}}\)All options have the \(\mathrm{CH_{3}CO} \) group except for option (c), which ends with \(\mathrm{COOH}\). Option (a), (b), and (d) have potential to produce iodoform.

Step 3: Identify the Option Producing Sodium Succinate

Sodium succinate is the sodium salt of succinic acid, which is a dicarboxylic acid (HOOC-(CH2)2-COOH). Upon reaction with \(\mathrm{NaOH}\) and \(\mathrm{I_2}\), only certain structures will form sodium succinate after oxidation. Since methyl ketone compounds (with an additional dicarboxylic behavior at the correct position) can result in such a product, check which options can form sodium succinate.

Step 4: Evaluate (c) for Sodium Succinate

Option (c) \(\mathrm{CH_{3}COCH_{2}CH_{2}COOH}\) can oxidize and rearrange via the haloform reaction to ultimately form \(\mathrm{NaOOC-(CH_2)_2-COONa}\) and iodoform. This is due to its structure enabling formation of two \(\mathrm{COOH}\) groups post-reaction, leading to sodium succinate.

Step 5: Conclusion

After evaluating all conditions, option (c) \(\mathrm{CH_{3}COCH_{2}CH_{2}COOH}\) is the compound that upon warming with \(\mathrm{I_2}\) and \(\mathrm{NaOH}\) forms iodoform and sodium succinate.

Key Concepts

Methyl Ketone

Methyl ketones are an important class of organic compounds characterized by the functional group \( \text{CH}_3\text{CO} \). The simplest methyl ketone is acetone, but many others exist, each with unique properties. All methyl ketones have in common the reactive acyl carbon center directly attached to a methyl group. This arrangement allows these compounds to easily participate in reactions where the methyl group can be oxidized or otherwise modified.
Methyl ketones are commonly tested for in organic chemistry through specific reactions, such as the iodoform test. This reaction identifies compounds that possess the \( \text{CH}_3\text{CO} \) structure by forming the yellow precipitate, iodoform (\( \text{CHI}_3 \)). The presence of this yellow solid confirms the presence of a methyl ketone in the compound being tested.

Sodium Succinate

Sodium succinate is the sodium salt derived from succinic acid, an organic compound with the formula \( \text{HOOC-(CH}_2)_2\text{-COOH} \). This molecule is a vital intermediate in the citric acid cycle, playing an essential role in cellular respiration in many organisms. In the context of organic reactions, sodium succinate is relevant because it can be formed when certain dicarboxylic compounds react with bases.
Here, the formation of sodium succinate indicates that the structure of the tested compound has reacted in a manner that introduces two carboxylate ions. This typically occurs through oxidative or rearrangement reactions where available carbonyl groups or other functional groups are transformed. The resulting sodium succinate can be detected through its distinct chemical properties, indicative of the structural makeup of the original compound.

Chemical Test for Methyl Ketones

The iodoform test is a principal chemical test for detecting the presence of methyl ketones. This test is popular in practical organic chemistry because of its specificity and simplicity. To perform the iodoform test, iodine is mixed with an aqueous solution of sodium hydroxide and the tested compound.

• If the compound contains a methyl ketone group \( \text{CH}_3\text{CO} \), the test will result in the formation of iodoform (\( \text{CHI}_3 \)), a yellow solid with a distinct odor.
• The generation of the yellow precipitate is considered a positive test, confirming the presence of methyl ketones or alcohols that can oxidize to methyl ketones in the chemical structure.

This test is not only utilized for academic purposes but also in various industrial applications where the presence of methyl ketones needs verification.

Organic Chemistry Reactions

Organic chemistry is rich with diverse reactions that transform compounds, yielding new products with varied functionality. The iodoform reaction is just one example of the many transformations that are studied. As a distinctive reaction, it highlights the reactivity of methyl ketone groups and introduces the concept of oxidative halogenation.
Organic chemistry reactions often involve:

• Oxidation and reduction processes where electrons are transferred, changing the oxidation state of involved atoms.
• Addition reactions requiring breaking and forming of chemical bonds, allowing new atoms or groups to attach to a molecule.
• Substitution reactions where one atom or group is replaced by another, a common mechanism seen in halogenations such as the iodoform reaction.

These reactions underpin the synthesis of many compounds and materials vital to everyday life. Proper understanding of these reactions allows chemists to predict and manipulate chemical changes in targeted ways, producing specific outcomes from a set of starting materials.