A yellow coloured compound formed when methyl ketone is oxidised by sodium hypoiodite is:

$CHI_3$

The correct answer is Option (2) → $CHI_3$

The reaction between methyl ketones and sodium hypoiodite (\(NaOI\)) is a classic example in organic chemistry, often referred to as the haloform reaction. This reaction is notable for producing iodoform (\(CHI_3\)), a yellow-colored compound with antiseptic properties. Let’s delve into the details of the process.

Background on Methyl Ketones

Methyl ketones are compounds that have the structure \(R-CO-CH_3\), where \(R\) can be any alkyl group. Acetone (\(CH_3COCH_3\)) is a common example of a methyl ketone

Sodium Hypoiodite

Sodium hypoiodite is a compound with the formula \(NaOI\). It acts as a halogenating agent, providing iodine in a reactive form, which can oxidize the methyl ketone.

The Haloform Reaction

The haloform reaction involves the following key steps:

Oxidation of Methyl Ketone

When a methyl ketone is treated with sodium hypoiodite, the following oxidation occurs:

The methyl group (\(-CH_3\)) adjacent to the carbonyl group is oxidized.

This leads to the cleavage of the carbon-carbon bond, resulting in the formation of iodoform and a carboxylic acid.

Mechanism

Formation of Iodinated Intermediate:

The methyl group is sequentially iodinated to form a triiodomethyl group (\(-C(=O)-CI_3\)).

\(RCOCH_3 + 3 NaOI \rightarrow RCOCI_3 + 3 NaOH\)

Cleavage and Formation of Iodoform:

The triiodomethyl compound undergoes further reaction with hydroxide ions (from \(NaOH\)), leading to the cleavage of the carbon-carbon bond and the formation of iodoform and the carboxylate ion.

\(RCOCI_3 + OH^- \rightarrow CHI_3 + RCOO^-\)

Characteristics of Iodoform

Iodoform is a yellow crystalline solid that is often used as an antiseptic.

It has a distinct medicinal smell and is soluble in alcohol and chloroform.

Iodoform can react with bases and can also be hydrolyzed to yield iodide ions.

Applications

Due to its antiseptic properties, iodoform is sometimes used in medicinal applications. It serves as a reagent in various organic synthesis reactions.

Conclusion

In summary, when methyl ketones are oxidized by sodium hypoiodite, they undergo a reaction that produces iodoform (\(CHI_3\)). The mechanism involves the oxidation and cleavage of the carbon chain, leading to the formation of the yellow compound, which is of significant interest in both organic chemistry and medicinal applications. Thus, the correct answer to the question is: \(CHI_3\) (Iodoform).