Problem 40 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following reactants will react with phenol to give salicylaldehyde after hydrolysis? (a) methyl chloride (b) trichloromethane (c) dichloromethane (d) none of these

Step-by-Step Solution

Answer

The reactant that forms salicylaldehyde with phenol is trichloromethane (b).

Step 1: Identify the Reaction

The reaction we need to identify is the Reimer-Tiemann reaction. This involves the conversion of phenol to salicylaldehyde.

Step 2: Recall Reimer-Tiemann Reaction Reagents

The Reimer-Tiemann reaction uses chloroform (trichloromethane, item b) and a strong base like sodium hydroxide to form salicylaldehyde from phenol.

Step 3: Determine Reactant Match

Out of the given options, trichloromethane (b) is the compound that aligns with the typical reagent used in the Reimer-Tiemann reaction that converts phenol to salicylaldehyde.

Key Concepts

Salicylaldehyde

Salicylaldehyde is an organic compound known for its characteristic almond-like odor. This chemical compound belongs to the family of benzaldehydes and is an essential precursor in the production of several chemical compounds and pharmaceuticals. In the Reimer-Tiemann reaction, salicylaldehyde is synthesized from phenol. During this reaction, the hydrogen at the ortho position (next to the hydroxyl group) of phenol is replaced by an aldehyde group, effectively converting phenol into salicylaldehyde. This transformation is significant because it introduces the aldehyde functional group in an ortho position relative to the hydroxy group, which is key to its unique reactivity and chemical properties. Salicylaldehyde is used as a flavoring agent and in perfumery; its reactivity also makes it useful in various biochemical applications.

Chloroform

Chloroform, also known as trichloromethane, is a colorless, sweet-smelling organic compound with the formula \(CHCl_3\). It has been used historically as an anesthetic and as a precursor to other chemicals in the industry.When it comes to the Reimer-Tiemann reaction, chloroform plays a critical role as a reactant. The presence of chloroform and a strong base like sodium hydroxide initiates a series of chemical transformations.

• Chloroform reacts under basic conditions to produce a dichlorocarbene intermediate.
• This reactive intermediate facilitates the insertion of an aldehyde group into the ortho position of phenol, leading to the formation of salicylaldehyde.

Chloroform's capability to produce such taxonomically important intermediates makes it indispensable in many organic synthesis processes.

Sodium Hydroxide

Sodium Hydroxide, also known as lye or caustic soda, is a strong base with the chemical formula \(NaOH\). It is widely used in households and industries for soap making, paper production, and other processes.In the context of the Reimer-Tiemann Reaction, sodium hydroxide serves as a vital catalyst and base. Its primary function is:

• To generate a basic environment that allows chloroform to form the dichlorocarbene intermediate.
• The basic conditions are necessary for deprotonating phenol, increasing its nucleophilicity, so it can effectively react with the intermediate to add an aldehyde group.

This function illustrates sodium hydroxide's utility beyond common household uses, underscoring its importance in facilitating reactions like the Reimer-Tiemann Reaction in the field of organic chemistry.