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) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}+\mathrm{CHCl}_{3}+\mathrm{KOH}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}+\mathrm{CHCl}_{3}+\mathrm{KOH}\)

Step-by-Step Solution

Answer

Option (d) 06H5OH + CHCl3 + KOH is used in the Reimer-Tiemann reaction.

Step 1: Understand the Reimer-Tiemann Reaction

The Reimer-Tiemann reaction is a chemical reaction used to form ortho-formyl phenols. It typically involves the reaction of phenol with chloroform and a base, like potassium hydroxide (KOH), to introduce an aldehyde group into the aromatic ring.

Step 2: Identify the Reactants in Each Option

Examine each set of reactants given in the options: - Option (a): Phenol (06H5OH), Carbon dioxide (CO2), Potassium hydroxide (KOH) - Option (b): Aniline (06H5NH2), Methyl chloride (CH3Cl), Potassium hydroxide (KOH) - Option (c): Aniline (06H5NH2), Chloroform (CHCl3), Potassium hydroxide (KOH) - Option (d): Phenol (06H5OH), Chloroform (CHCl3), Potassium hydroxide (KOH)

Step 3: Match the Reactants to the Reaction's Requirements

Compare each option with the standard reactants in a Reimer-Tiemann reaction: phenol, chloroform, and a base. - Option (a) has phenol and KOH but uses CO2 instead of chloroform, so it does not match. - Option (b) uses aniline and methyl chloride, so it is incorrect. - Option (c) uses aniline, not phenol, hence it is incorrect. - Option (d) contains phenol, chloroform, and KOH, which are the correct reactants for the Reimer-Tiemann reaction.

Step 4: Select the Correct Option

Now that we have identified option (d) as having the correct set of reactants for the Reimer-Tiemann reaction, we can conclude this is the correct answer.

Key Concepts

Ortho-formyl Phenols

In organic chemistry, ortho-formyl phenols are an important category of compounds characterized by having an aldehyde group directly attached to the aromatic ring's ortho position, that is, the position directly adjacent to the hydroxyl (OH) group. This strategic position allows these compounds to have interesting chemical properties.
Ortho-formyl phenols are key intermediates in many synthetic pathways and are used in various applications, including the synthesis of pharmaceuticals and other aromatic compounds. What's fascinating is that this structure not only stabilizes the molecule but also influences reactivity patterns.
The Reimer-Tiemann reaction is renowned for its ability to specifically form ortho-formyl phenols from phenol by selectively introducing the aldehyde group into the ortho position. This reaction carefully exploits the electronic characteristics of the phenolic ring, thereby allowing this selectivity.

Chemical Reaction

A chemical reaction is an impactful process whereby compounds, known as reactants, undergo a transformation to form products with different properties. This fundamental activity in chemistry involves the breaking and formation of bonds, facilitating new substances.
In the Reimer-Tiemann reaction, the main conversion process illustrates this concept perfectly, where phenol reacts with chloroform in the presence of a strong base. This reaction results in a new compound, ortho-formyl phenol, showcasing a clear example of how chemical reactions create new functionalities by altering molecular structures.
This transformation occurs through several stages, including the formation of intermediates, making it essential for organic chemists to predict and control these reactions to efficiently facilitate the desired reactions.

Phenol

Phenol, also known as carbolic acid, is a crucial compound in organic chemistry with the chemical formula \( ext{C}_6 ext{H}_5 ext{OH}\). It features a benzene ring bonded to a hydroxyl group and serves as a foundational reactant in the Reimer-Tiemann reaction. Its ability to donate a hydrogen atom from its hydroxyl group makes it an ideal aromatic substrate for introducing an aldehydic group in the ortho position.
The aromatic character of phenol leads to enhanced stability, allowing it to undergo transformations with relatively low energy input compared to other molecules. This property of phenol facilitates its efficient conversion into ortho-formyl phenols during the Reimer-Tiemann reaction, highlighting phenol's importance in synthetic organic processes.
Despite its utility, phenol is also a relatively reactive compound, meaning chemists must handle it with care to mitigate unwanted side reactions or degradation during the synthesis.

Chloroform

Chloroform, or trichloromethane, is a versatile solvent with the formula \( \text{CHCl}_3 \) and plays a pivotal role in the Reimer-Tiemann reaction. This compound serves as a source of dichlorocarbene, a highly reactive intermediate.
In this reaction, chloroform, in the presence of a strong base like potassium hydroxide, can form dichlorocarbene. This intermediate attacks the phenolic ring, facilitating the transformation into ortho-formyl phenols.
Chloroform's properties as a non-hydrocarbon chlorinated solvent make it particularly effective in many organic reactions beyond the Reimer-Tiemann reaction. However, its volatility and potential health risks require careful handling in lab settings.

Potassium Hydroxide

Potassium hydroxide, KOH, is a strong base employed in the Reimer-Tiemann reaction to generate the reactive dichlorocarbene from chloroform. Its role in this reaction extends beyond simple deprotonation, as it plays a crucial part in facilitating the formation of intermediates and progressing the reaction towards the final ortho-formyl phenolic product.
One of the key properties of potassium hydroxide is its ability to cleave molecules, particularly through reactions forming carbenes, which are crucial intermediates in many organic syntheses. In the Reimer-Tiemann mechanism, KOH attacks chloroform to release dichlorocarbene, an essential step for the continued transformation of reactants into the desired aromatic aldehyde.
Potassium hydroxide's high reactivity is advantageous in making the Reimer-Tiemann reaction efficient and productive, helping to overcome potential barriers that might otherwise slow down the reaction process. Despite its efficacy, its caustic nature necessitates careful handling to prevent chemical burns or other hazards in a safety-conscious laboratory environment.