Problem 37 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following sets of reactants is used in Reimer-Tiemann reaction? (a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}+\mathrm{CO}_{2}+\mathrm{KOH}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}+\mathrm{CH}_{3} \mathrm{Cl}+\mathrm{KOH}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}^{2}+\mathrm{CHCl}_{3}+\mathrm{KOH}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{4} \mathrm{OH}+\mathrm{CHCl}_{3}+\mathrm{KOH}\)

Step-by-Step Solution

Answer

Option (d) is the correct set of reactants for the Reimer-Tiemann reaction.

Step 1: Understand the Reimer-Tiemann Reaction

The Reimer-Tiemann reaction is an organic chemical reaction used to convert phenols into ortho-hydroxybenzaldehydes using chloroform and a strong base.

Step 2: Identify the Required Reactants

For this reaction to proceed, the reactants involved must include phenol ( C_{6}H_{5}OH ), chloroform ( CHCl_{3} ), and a strong base such as potassium hydroxide ( KOH ).

Step 3: Analyze Each Option

(a) uses C_{6}H_{5}OH (phenol), but CO_{2} is not required. (b) involves C_{6}H_{5}NH_{2} and CH_{3}Cl , which are not reactants for this reaction. (c) includes C_{6}H_{5}NH_{2}^{2} and CHCl_{3} , but C_{6}H_{5}NH_{2}^{2} is incorrect. (d) features C_{6}H_{5}OH (phenol, possibly misprinted as C_{6}H_{4}OH ), CHCl_{3} , and KOH , matching the correct reactants.

Step 4: Confirm the Correct Answer

Based on the chemical requirements and the options provided, option (d) is correct, albeit with a possible typographical error in the chemical formula for phenol. The required reactants for the Reimer-Tiemann reaction are phenol, chloroform, and potassium hydroxide, making this the choice in line with known chemical processes.

Key Concepts

Organic Chemistry Reactions

Organic chemistry involves many fascinating reactions where chemicals are transformed into different compounds. One interesting class of such reactions is those involving functional group conversions, like the Reimer-Tiemann Reaction. These reactions play a vital role in the synthesis of complex organic molecules and are pivotal in both academic and industrial chemistry.

In essence, organic reactions involve a series of steps where bonds are broken and formed, leading to the conversion of reactants into desired products. This transformation often involves reagents and catalysts, promoting the reaction under specific conditions such as temperature or pH.

• Understand the reactants: typically the starting materials.
• Recognize the role of catalysts: substances that speed up the reaction without being consumed.
• Know the conditions: like temperature and pH needed for the reaction to occur.

Grasping these principles is crucial as it helps predict the products of reactions and how they proceed.

Phenols to Ortho-Hydroxybenzaldehydes

In the context of the Reimer-Tiemann Reaction, phenols, like phenol (\(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{OH}\)), are transformed into valuable chemical compounds known as ortho-hydroxybenzaldehydes. This conversion is particularly useful in creating aldehydes, which are important in constructing more complex organic compounds.

Ortho-hydroxybenzaldehydes feature both a hydroxyl group and an aldehyde group adjacent to one another on a benzene ring. This arrangement makes them versatile in further chemical reactions, broadening their utility in synthetic chemistry.

• Ortho position: Refers to substituents that are adjacent on the benzene ring.
• Significance: These compounds are precursors to more complex molecules.
• Applications: Widely used in the pharmaceutical and fragrance industries.

Understanding these specifics can offer insights into how the Reimer-Tiemann Reaction fits into the broader landscape of organic synthesis.

Reaction Mechanisms

The Reimer-Tiemann Reaction involves specific steps at the molecular level, all part of what is known as the reaction mechanism. Mechanisms provide a detailed pathway, illustrating how reactants are converted into products through intermediates and transition states.

For the Reimer-Tiemann Reaction, the mechanism begins with the formation of a dichlorocarbene intermediate from chloroform and a strong base like potassium hydroxide. This intermediate is highly reactive and attacks the phenol \((\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{OH})\), leading to the formation of the ortho-formylphenol.

• Dichlorocarbene: A key intermediate that reacts with phenol.
• Transition states: High-energy states the reaction passes through.
• Rate of reaction: Influenced by the stability of intermediates and transition states.

Knowing the steps and intermediates in a reaction mechanism is invaluable for students and chemists alike, as it enables the prediction and control of chemical reactions.