Problem 210 - A Complete Resource Book in Chemistry for JEE Main

Question

Bakelite is obtained from phenol by reacting with (a) \(\left(\mathrm{CH}_{2} \mathrm{OH}\right)_{2}\) (b) \(\mathrm{CH}_{3} \mathrm{CHO}\) (c) \(\mathrm{CH}_{4} \mathrm{COCH}_{3}\) (d) \(\mathrm{HCHO}\)

Step-by-Step Solution

Answer

Bakelite is formed by reacting phenol with (d) ext{HCHO}.

Step 1: Identifying Bakelite Formation

Bakelite is a type of phenolic resin. It is formed through the reaction of phenol with formaldehyde. The process involves an elimination reaction leading to a highly cross-linked polymer.

Step 2: Recognizing the Correct Reactant

Out of the options given, the correct reactant for forming Bakelite with phenol is formaldehyde, represented as \( ext{HCHO}\). The others are not involved in the formation of Bakelite.

Step 3: Conclusion

After identifying \( ext{HCHO}\) (formaldehyde) as the reactant for phenol, it's concluded that option (d) \( ext{HCHO}\) is the correct choice.

Key Concepts

Phenol-Formaldehyde Reaction

The phenol-formaldehyde reaction is the foundational process in creating various types of polymeric materials, most notably Bakelite. This reaction stands out due to its simplicity and efficiency.

When phenol interacts with formaldehyde, a series of chemical reactions occur that lay the groundwork for creating a robust polymer network.

• Initially, phenol and formaldehyde react to form a compound called a phenolic hydroxymethyl derivative.
• This intermediate then undergoes further polymerization to form complex network structures.

In these early stages, the reaction primarily occurs through an elimination-then-addition mechanism, promoting the formation of water as a by-product. Through these consecutive condensation reactions, smaller molecular units combine to create larger, more intricate assemblies.

The most common form of the phenol-formaldehyde reaction produces what's known as a thermosetting polymer, meaning once cured, the material remains in a permanent shape and resists melting. This distinct feature makes products like Bakelite exceptionally valuable in industrial applications where extreme durability is required.

Cross-Linked Polymer

A cross-linked polymer is a large web-like structure composed of long polymer chains interconnected by cross-links. This multipoint connection between chains is what grants the resulting material enhanced strength and stability. In the scope of Bakelite formation, these characteristics are particularly significant.

During the reaction of phenol with formaldehyde, cross-linking occurs through methylene bridges. These are simply groups that act as links holding the molecular chains together firmly.

• Such cross-linked structures help resist deformation under stress.
• They enhance the overall rigidity and thermal stability of the polymer.

As a result of this intricate network of linkages, Bakelite and similar phenolic resins become incredibly strong despite their relatively simple starting components.

This cross-linking property is key for applications that require high-performance materials that cannot be easily reformed once set, such as electrical insulators, components in automotive industries, and certain types of cookware.

Phenolic Resin

Phenolic resins are synthetic polymers derived from the reaction between phenol and formaldehyde. They were among the first to be created and used commercially, largely because of their rugged thermal and chemical resistance.

Here's how phenolic resins, specifically Bakelite, meet practical needs:

• They are non-conductive, making them ideal for electrical applications such as sockets and switches.
• Their ability to withstand thermal and chemical strain makes them suitable for kitchenware like handles and knobs.

Moreover, these materials possess excellent adhesive properties, which have led to their use in coatings, adhesives, and even as a binder in molding compounds.

Phenolic resins are often celebrated for being both economical and highly functional. This combination ensures that they remain a staple choice in various industrial spheres, long after their initial emergence in the early 20th century.