Question

Choose the incorrect option(s): (A) is Clemmensen reduction (B) Tollen's and Fehling reagent are strong oxidising agent and can be reduced by acetone (C) Aldehyde can be easily oxidised to acids with nitric acid, potassium permanganate and potassium dichromate (D) Methyl ketones are oxidised by sodium hypohalite

Short answer

The incorrect option is (B) Tollen's and Fehling reagent are strong oxidising agents and can be reduced by acetone.

Step-by-step solution

Analyze statement (A)

"is Clemmensen reduction" Clemmensen reduction is a reaction in organic chemistry where an aldehyde or a ketone is converted into an alkane by using zinc amalgam (Zn-Hg) and concentrated hydrochloric acid (HCl). This statement is incomplete and doesn't provide enough context to understand its correctness. However, we assume it is supposed to say: "Clemmensen reduction is a method used to reduce aldehydes and ketones". In that case, statement (A) would be correct.

Analyze statement (B)

"Tollen's and Fehling reagent are strong oxidising agents and can be reduced by acetone" Tollen's reagent (ammoniacal silver nitrate) and Fehling's reagent are strong oxidizing agents that can oxidize aldehydes, but are not capable of oxidizing ketones. Acetone is a ketone and won't be able to reduce these reagents. Hence, statement (B) is incorrect.

Analyze statement (C)

"Aldehyde can be easily oxidized to acids with nitric acid, potassium permanganate, and potassium dichromate" Aldehydes can indeed be easily oxidized to carboxylic acids with the help of strong oxidizing agents like nitric acid (HNO₃), potassium permanganate (KMnO₄), and potassium dichromate (K₂Cr₂O₇). Statement (C) is correct.

Analyze statement (D)

"Methyl ketones are oxidized by sodium hypohalite" Methyl ketones (ketones containing a CH3CO group) can be selectively oxidized by halogen-containing oxidizing agents like sodium hypochlorite (NaOCl) or sodium hypobromite (NaOBr) to yield carboxylic acids and haloforms (compounds containing C-X bonds, where X represents halogens). This reaction is called the haloform reaction. Statement (D) is correct.

Identify the incorrect statement(s)

Based on the analysis of all the given statements, the incorrect option is: (B) Tollen's and Fehling reagent are strong oxidising agents and can be reduced by acetone

Key concepts

Clemmensen Reduction

Clemmensen reduction is a classic reaction used in organic chemistry to reduce aldehydes and ketones to alkanes. This reaction involves treating the carbonyl compound with a mixture of zinc amalgam (zinc-mercury alloy) and strong hydrochloric acid. The reaction conveniently converts the carbonyl functional group \(\text{C=O}\) into a methylene group \(\text{-CH2}-\), effectively removing the oxygen atoms.

It is particularly useful when other sensitive functionalities are present in the molecule which need to be retained, as Clemmensen reduction conditions do not typically affect other functional groups. This reaction is applied in synthesis when gentler methods like catalytic hydrogenation aren't suitable, especially if the compound is not stable under acidic conditions.

Tollen's Reagent

Tollen's reagent, often abridged in literature as 'the silver mirror test,' is a qualitative analytical tool used to detect the presence of aldehydes. It consists of ammoniacal silver nitrate \(\text{Ag(NH3)2}^+\) and reacts with aldehydes to form a silver mirror on the inner walls of a test tube or to precipitate out silver metal. Tollen's reagent does not react with ketones, which helps in distinguishing between aldehydes and ketones.

Importance in JEE Organic Chemistry

Understanding Tollen's reagent is crucial for students prepping for the JEE, as it underlines the functional group analysis in organic compounds. Its specificity for aldehydes over ketones can help in identifying unknown compounds in reaction mixtures.

Fehling's Reagent

Similar to Tollen's reagent, Fehling's reagent is used as a chemical test to differentiate between water-soluble aldehydes and ketones. The reagent comprises a complex mixture of copper(II) sulfate, sodium potassium tartrate (Rochelle salt) and a strong base like NaOH. Upon reaction with an aldehyde, Fehling's solution changes color from blue to a brick red precipitate of copper(I) oxide.

Reaction Specificity

Like Tollen's reagent, it does not react with all ketones; thus, providing a straightforward method for telling apart aldehydes from ketones. Its oxidation mechanism and the appearance of a color change make this reagent instructional for understanding the principles of redox reactions within a JEE context.

Oxidation of Aldehydes

When discussing the oxidation of aldehydes, we refer to the chemical process of transforming an aldehyde into a carboxylic acid. Several oxidizing agents can effect this transformation, including nitric acid (HNO3), potassium permanganate (KMnO4), and potassium dichromate (K2Cr2O7).

Oxidation Mechanism

The reaction mechanism typically occurs via the formation of a hydrate followed by the loss of hydrogen atoms, eventually replacing the aldehyde group with a carboxylic acid group. Recognizing the oxidation states and the electron transfers involved in these reactions is a fundamental skill in preparation for the JEE examination, vital for unraveling complex organic reaction mechanisms.

Haloform Reaction

The haloform reaction is characteristic of methyl ketones but can also occur with secondary alcohols that have at least one methyl group next to the functional group. This reaction involves the halogenation in the presence of a base such as sodium hydroxide, to produce a haloform \(CHX3\), where X is the halogen. The remaining fragment of the original molecule becomes a carboxylate ion, which in acidic solution can form a carboxylic acid.

Role in Structure Elucidation

Understanding this reaction is essential for JEE organic chemistry as it is a vital test for the identification of methyl ketones and for the determination of molecular structure. It is also a valuable synthetic strategy to transform ketones into carboxylic acids and illustrates the intricacy of organic reaction mechanisms.