Disproportionation

Definition

Disproportionation is a chemical reaction in which a single reactant is simultaneously oxidized and reduced, resulting in the formation of two or more different products. This process is an important concept in various areas of organic chemistry, including radical reactions, radical additions to alkenes, radical halogenation of alkanes, and chain-growth polymerization.

5 Must Know Facts For Your Next Test

1. Disproportionation reactions are commonly observed in radical chain reactions, where a radical intermediate can react with another radical to form two different products.
2. In radical additions to alkenes, disproportionation can occur between two alkyl radicals, leading to the formation of an alkane and an alkene.
3. Radical halogenation of alkanes, such as the formation of alkyl halides, can involve disproportionation steps where a halogen radical reacts with an alkyl radical.
4. Disproportionation plays a crucial role in chain-growth polymerization, where radical intermediates can react with each other to terminate the polymer chain or initiate a new one.
5. The ability of disproportionation to generate a variety of products from a single reactant makes it an important process in organic synthesis and polymer chemistry.

Review Questions

• Explain how disproportionation reactions occur in radical chain reactions.
  • In radical chain reactions, disproportionation can occur when a radical intermediate reacts with another radical. This process involves the simultaneous oxidation and reduction of the reactants, leading to the formation of two different products. For example, two alkyl radicals may disproportionate to form an alkane and an alkene. This disproportionation step is a crucial part of the mechanism in various radical reactions, such as radical additions to alkenes and radical halogenation of alkanes.
• Describe the role of disproportionation in chain-growth polymerization.
  • Disproportionation plays a significant role in chain-growth polymerization reactions, which involve the sequential addition of monomers to a growing polymer chain. During the polymerization process, radical intermediates can undergo disproportionation reactions, where they react with each other to either terminate the polymer chain or initiate a new one. This disproportionation step can influence the molecular weight distribution and the overall properties of the resulting polymer, making it an important consideration in the synthesis of chain-growth polymers.
• Analyze how disproportionation reactions can lead to the formation of diverse products in organic synthesis.
  • The ability of disproportionation reactions to generate a variety of products from a single reactant makes them valuable in organic synthesis. By carefully controlling the reaction conditions and the nature of the radical intermediates, chemists can leverage disproportionation to produce a range of desired products. For example, in radical halogenation of alkanes, disproportionation between an alkyl radical and a halogen radical can lead to the formation of both alkyl halides and hydrogen halides, providing a versatile approach to the synthesis of alkyl halides. Similarly, in radical additions to alkenes, disproportionation between two alkyl radicals can yield both alkanes and alkenes, expanding the scope of possible products. The flexibility and diversity of outcomes offered by disproportionation reactions make them an important tool in the arsenal of organic chemists.

Related terms

Redox Reaction: A redox (reduction-oxidation) reaction is a type of chemical reaction where one reactant is oxidized (loses electrons) while another is reduced (gains electrons).

Radical Intermediate: A radical intermediate is a highly reactive species that contains an unpaired electron, which can participate in disproportionation reactions.

Chain-Growth Polymerization: Chain-growth polymerization is a type of polymerization reaction where monomers are added one at a time to a growing polymer chain, often involving radical intermediates.