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Chapter 16: Problem 58

The step-growth polymer nylon 6 is prepared from caprolactam. The reaction involves initial reaction of caprolactam with water to give an intermediate open-chain amino acid, followed by heating to form the polymer. Propose mechanisms for both steps, and show the structure of nylon 6 .

Short Answer

Expert verified
Caprolactam reacts with water to form 6-aminocaproic acid, which polymerizes to form nylon 6.

Step by step solution

01

Reaction of Caprolactam with Water

The first step in the synthesis of nylon 6 involves the ring-opening of caprolactam by water. When caprolactam reacts with water, it forms 6-aminocaproic acid. This occurs via a nucleophilic attack in which a water molecule attacks the carbonyl carbon of caprolactam, breaking the amide bond and opening the ring to form the open-chain structure of 6-aminocaproic acid. The structural transformation can be represented as:\[ \text{Caprolactam (C_6H_{11}NO)} + \text{H_2O} \rightarrow \text{6-Aminocaproic acid (C_6H_{13}NO_2)} \]
02

Polymerization of 6-Aminocaproic Acid

The second step involves the polymerization of 6-aminocaproic acid. When heated, 6-aminocaproic acid undergoes condensation polymerization. This entails the repetitious reaction of the amine end of one monomer with the carboxylic acid end of another, forming amide bonds, and with the release of water as a by-product, resulting in the formation of the polyamide chain.The general reaction can be expressed as:\[ n \text{6-Aminocaproic acid} \rightarrow \text{(-NH-(CH_2)_5-CO-)\(_n\)} + (n-1) \text{H_2O} \]This repeated linkage through amide bonds forms the polymer known as nylon 6.
03

Structure of Nylon 6

Nylon 6 is a polymer consisting of repeating units of [-NH-(CH_2)_5-CO-]. By arranging these repeating units in a chain, the structure of nylon 6 can be depicted. Each repeating unit is connected through amide linkages, which are formed through the reaction of an amine group and a carboxyl group in a condensation reaction.The structural formula of nylon 6 can be summarized as:\[ \text{[ -NH-(CH_2)_5-CO- ]}_n \]where 'n' represents the number of repeating units in the polymer chain.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Step-Growth Polymerization
Step-growth polymerization is a process used to form polymers by combining monomers with functional groups that can react to form chemical bonds. This is different from chain-growth polymerization, which involves the addition of monomers one at a time to a growing chain. In step-growth polymerization:
  • Monomers connect through reactions between two complementary functional groups, like an acid and an alcohol or amine.
  • The process often leads to the formation of small by-products, such as water or hydrogen chloride.
  • At each step, any two reactive molecules can combine, leading to a rapid increase in molecular weight.
  • This method often requires heat or catalysts to progress efficiently.
Nylon 6 is synthesized by a step-growth mechanism, primarily involving 6-aminocaproic acid monomers forming amide bonds in a chain reaction.
Caprolactam
Caprolactam is a cyclic amide, or lactam, with the chemical formula \(\text{C}_6\text{H}_{11}\text{NO}\). It is the precursor in the production of nylon 6, and its role in the synthesis of nylon is crucial. The process starts when caprolactam undergoes hydrolysis when reacting with water, which opens its ring to form 6-aminocaproic acid. Important aspects of caprolactam include:
  • Its structure features a ring with nitrogen and a carbonyl carbon, which are key to its reactivity.
  • Caprolactam's ring-opening requires a nucleophilic attack, usually initiated by water to break the amide bond.
  • This reaction transforms the cyclic caprolactam into a linear structure, enabling further reactions to form polymers.
This transformation is the first critical step in creating nylon 6, facilitating the polymerization process that follows.
6-Aminocaproic Acid
6-Aminocaproic acid is the open-chain compound resulting from the ring-opening of caprolactam when it reacts with water. It contains both amine (-NH\(_2\)) and carboxylic acid (-COOH) functional groups. These groups are vital for its role in polymerization.
  • After formation, 6-aminocaproic acid can link to itself through reactions between its amine and carboxylic ends.
  • The functional groups facilitate the formation of amide bonds, essential for creating polyamide chains like nylon 6.
  • The linear structure and reactivity of this molecule allow a seamless transition from a simple monomer to a complex polymer.
This compound is the active monomer for nylon 6 formation, enabling step-growth polymerization.
Condensation Polymerization
Condensation polymerization is a type of step-growth polymerization where monomers join to form a polymer and release a small molecule, often water, as a by-product. This is the main reaction pathway used in creating nylon 6 from 6-aminocaproic acid. Key features of condensation polymerization include:
  • The formation of polymer chains through repeated reactions between functional groups, typically amine and carboxylic acid.
  • The elimination of small molecules, which requires effective management to ensure strong polymer chains.
  • Each connecting reaction forms a new amide bond, adding to the length and complexity of the polymer.
  • Heat and sometimes catalysts are usually employed to aid the polymerization process.
This process is crucial for synthesizing nylon 6, as it turns individual 6-aminocaproic acid molecules into the long, durable polymer chains that characterize this material.

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Most popular questions from this chapter

How would you convert \(N\) -ethylbenzamide to each of the following products? (a) Benzoic acid (b) Benzyl alcohol (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{NHCH}_{2} \mathrm{CH}_{3}\)

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