Birch reduction

What is Birch reduction?

The Birch reduction is a chemical reaction that involves the reduction of an aromatic compound to a corresponding alkylbenzene. This reaction is named after the Australian chemist Arthur Birch, who first described it in the 1950s..

Birch reduction
Birch reduction

The Birch reduction is typically carried out using a reducing agent such as sodium in liquid ammonia, which is capable of reducing the aromatic compound to the corresponding alkylbenzene. The reaction can be represented as follows:

Aromatic Compound + Sodium in Liquid Ammonia -> Alkylbenzene

There are a number of different variations of the Birch reduction, depending on the specific reactants and conditions used. In some cases, the aromatic compound may be substituted with various groups, which can influence the reactivity and selectivity of the reduction..

The Birch reduction has a number of important applications in the synthesis of complex organic molecules. It has been used to synthesize a variety of natural products and other biologically active compounds, including alkaloids, terpenes, and other compounds. It has also been used in the synthesis of a number of pharmaceuticals and other compounds of industrial significance..

Overall, the Birch reduction is a powerful chemical reaction that has a wide range of applications in the synthesis of complex organic molecules. It has played a significant role in the development of many important compounds and continues to be an important tool in the field of chemistry..

Example

An example of the Birch reduction can be seen in the reduction of anisole to methoxybenzene. Anisole is an aromatic compound containing an oxygen atom bonded to the aromatic ring, while methoxybenzene is an alkylbenzene containing a methoxy group bonded to the aromatic ring..

The reduction of anisole to methoxybenzene can be achieved through the Birch reduction reaction, which can be represented as follows:

Anisole + Sodium in Liquid Ammonia -> Methoxybenzene

In this reaction, the anisole molecule is reduced by the sodium in liquid ammonia, resulting in the formation of the methoxybenzene product. This reaction is typically carried out at low temperatures in order to minimize the formation of unwanted side products..

Overall, this reaction represents an example of the Birch reduction, in which an aromatic compound is reduced to a corresponding alkylbenzene using sodium in liquid ammonia as the reducing agent. This reaction is an important synthetic tool in the field of chemistry and has a wide range of applications in the synthesis of complex organic molecules..

Mechanism of reaction

Birch reduction is a chemical reaction that reduces aromatic compounds to their corresponding hydrocarbons using sodium metal in liquid ammonia as the reducing agent. The reaction mechanism proceeds through several steps:

Formation of a complex between the aromatic compound and sodium: The first step in the Birch reduction is the formation of a complex between the aromatic compound and sodium. This is facilitated by the high solubility of sodium in liquid ammonia, which allows the sodium to dissolve and interact with the aromatic compound..
Deprotonation of the aromatic compound: The complex formed in the first step undergoes deprotonation, which involves the transfer of a proton from the aromatic compound to the solvent, liquid ammonia. This step results in the formation of an anion, or negative ion, of the aromatic compound..
Reduction of the anion: The anion formed in the second step is then reduced by the sodium atom, resulting in the formation of a radical anion of the aromatic compound. This radical anion is highly reactive and undergoes further reactions to form the final product..
Formation of the final product: The radical anion formed in the third step can undergo a variety of reactions, depending on the specific conditions of the reaction. In some cases, the radical anion may react with another molecule of the aromatic compound to form a dimer. In other cases, the radical anion may react with solvent molecules to form a variety of products, including the corresponding hydrocarbon..
Overall, the Birch reduction is a useful method for reducing aromatic compounds to their corresponding hydrocarbons, and it is often used in the synthesis of a variety of organic compounds..

References

  • A.J. Birch, J. Chem. Soc. 1944, 430
  • A.J. Birch, J. Chem. Soc. 1945, 809
  • A.J. Birch, J. Chem. Soc. 1946, 593
  • A.J. Birch, J. Chem. Soc. 1947, 102
  • A.J. Birch, J. Chem. Soc. 1947, 1642
  • A.J. Birch, J. Chem. Soc. 1949, 2531
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