Question

If $(\mathrm{P})$ have formula ${}^{‘}{\mathrm{C}}_3{\mathrm{H}}_6\mathrm{O}$ ' and gives (+ve) haloform test then incorrect option regarding following reaction sequence is : $(\mathrm{P})\stackrel{{\mathrm{NH}}_2-{\mathrm{NH}}_2}{⟶}(\mathrm{Q})\stackrel{\mathrm{KOH}\mathrm{\setminus }\mathrm{\Delta }}{⟶}(\mathrm{R})+(\mathrm{S})\mid$ (A) Reaction is known as Wolff Kishner reduction (B) (Q) is hydrazone (C) $(\mathrm{R})$ has molecular formula ${\mathrm{C}}_3{\mathrm{H}}_8$ (D) (S) is oxygen containing gas

Short answer

The incorrect option regarding the given reaction sequence is (D) S is an oxygen-containing gas. In the reaction, S is actually a mixture of nitrogen gas (N2) and water vapor (H2O), which although containing oxygen as a component, does not have a molecular formula that is an oxygen-containing gas.

Step-by-step solution

Compound P has the molecular formula ${}^{‘}{\mathrm{C}}_3{\mathrm{H}}_6\mathrm{O}$ ' and gives a positive haloform test. This means it must contain a CH3CO- group. The only compound with this formula containing that group is acetone (CH3COCH3). #Step 2: Reaction of P with NH2-NH2#

Acetone (P) reacts with hydrazine (NH2-NH2) to form a hydrazone (Q). The reaction can be written as: CH3COCH3 + N2H4 → CH3C(NH2)NHNH2 The product, Q, is an acetone hydrazone. #Step 3: Reaction of Q with KOH and heat#

Q, the acetone hydrazone, is reacted with KOH and heat. This reaction is known as the Wolff Kishner reduction. The products of this reaction are a hydrocarbon (R) and an oxygen-containing gas (S). The reaction can be represented as: CH3C(NH2)NHNH2 + KOH → CH3CH2CH3 + N2 + H2O So, R is propane ${\mathrm{C}}_3{\mathrm{H}}_8$ and S is a mixture of nitrogen gas (N2) and water vapor (H2O) which is an oxygen-containing gas. #Step 4: Evaluate the given options#

Now, let's evaluate the given options based on our analysis: (A) The reaction is known as the Wolff Kishner reduction: This statement is true. The Wolff Kishner reduction is the reaction of a hydrazone with KOH and heat to produce a hydrocarbon and an oxygen-containing gas. (B) Q is hydrazone: This statement is true. The reaction of P (acetone) with NH2-NH2 forms an acetone hydrazone (Q). (C) R has molecular formula ${\mathrm{C}}_3{\mathrm{H}}_8$: This statement is true. The product R is propane, which has the given molecular formula. (D) S is an oxygen-containing gas: This statement is false. S is a mixture of nitrogen gas (N2) and water vapor (H2O), which, while containing oxygen as a component, does not have a molecular formula that is an oxygen-containing gas. Therefore, the incorrect option is (D).

Key concepts

Haloform Test

The haloform test is a chemical reaction used to identify or confirm the presence of a methyl ketone in a compound. A positive haloform test typically indicates the presence of a structure with a

• methyl group (-CH₃)
• adjacent to a carbonyl group (C=O)

In the context of the problem, compound P has the molecular formula C₃H₆O, which corresponds to acetone (CH₃COCH₃) since it satisfies the requirement for a positive haloform test. This test is significant in organic chemistry for differentiating between various types of ketones and other compounds.

Molecular Formula

A molecular formula represents the number and type of atoms in a molecule. For compound P, the molecular formula is C₃H₆O. This means it contains:

• 3 carbon atoms
• 6 hydrogen atoms
• 1 oxygen atom

Given the formula, and knowing it gives a positive haloform test, we can infer the structural formula as acetone. The molecular formula gives us a clear picture of the potential hydrocarbon skeleton and functional groups present in the compound, allowing chemists to deduce the possible reactions and properties.

Acetone Hydrazone

Acetone hydrazone is formed when acetone reacts with hydrazine (NH₂-NH₂). This reaction involves substitution of the oxygen atom in the carbonyl group with a hydrazone linkage. The reaction can be represented by the equation:
CH₃COCH₃ + N₂H₄ → CH₃C(NH₂)NHNH₂
This results in compound Q, known as hydrazone. Hydrazones are significant in many organic synthesis routes due to their ability to form stable structures while being versatile intermediates. They are a key component of the Wolff Kishner reduction, as observed here.

Reaction Mechanism

In the Wolff Kishner reduction, the reaction mechanism transforms the hydrazone (Q) into a hydrocarbon (R) and gas (S) by heating it with KOH. Let's delve into the details of this mechanism:

• The reaction begins with the deprotonation of the hydrazone, forming an intermediate, where the hydrazone is coordinated with the base (KOH).
• Heat facilitates the release of nitrogen gas (N₂) from this intermediate, simultaneously forming an alkane (here, propane, C₃H₈).
• Water vapor (H₂O) is released as a byproduct, contributing to the oxygen component of the gas mixture (S).

The reaction mechanism is efficient for converting carbonyl groups to hydrocarbons, making it valuable in synthetic applications that require a reduction of ketones to alkanes while liberating minimal side products.