Béchamp reaction

What is Béchamp reaction?

The Béchamp reaction was firt described, in 1853, by the French chemist Antoine J. Béchamp (1816-1908) for the preparation of para-substituted arylarsonic acid by heating aromatic amine or phenol with arsenic acid. The reaction can be carried out for phenols, amines and derivatives.

Bechamp reaction
Béchamp reaction

This reaction is different from the Béchamp reduction, which is a reduction of an aldehyde or ketone using zinc dust and hydrochloric acid..

The Béchamp reaction involves the condensation of an aromatic amine or phenol with arsenic acid to form an arylarsonic acid. The reaction typically occurs at elevated temperatures, usually around 150-200 °C, and in the presence of a catalyst, such as sulfuric acid or hydrochloric acid..

The Béchamp reaction is a highly useful method for the preparation of para-substituted arylarsonic acids, which are important compounds in the synthesis of pharmaceuticals and other organic compounds. The reaction is particularly useful for the preparation of para-substituted arylarsonic acids, which are not easily obtained by other methods..

The Béchamp reaction is a versatile process, and it can be used to prepare a wide range of different arylarsonic acids. The reaction can be used to prepare both primary and secondary arylarsonic acids, and it can also be used to prepare arylarsonic acids with different substituents on the aromatic ring..

One of the key advantages of the Béchamp reaction is its high selectivity. It can produce a wide range of different arylarsonic acids from a single aromatic amine or phenol, and it typically provides high yields of the desired product..

The Béchamp reaction does have some limitations. The reaction requires the use of arsenic acid, which is a toxic and carcinogenic substance, and it also requires the use of elevated temperatures and pressures, which can be challenging to control. Additionally, the reaction typically requires the use of a catalyst, which can be difficult to handle and can be dangerous if inhaled..

Despite these limitations, the Béchamp reaction remains an important tool in the organic chemist’s arsenal. With its high selectivity and efficiency, the Béchamp reaction has played an important role in the development of many new compounds and pharmaceuticals. The reaction is widely used in organic synthesis for the preparation of para-substituted arylarsonic acids, which are important building blocks for many organic compounds..

Summary

Béchamp reaction is a powerful and versatile method for the preparation of para-substituted arylarsonic acids by heating aromatic amines or phenols with arsenic acid. While the process has some limitations, it has been widely adopted in organic synthesis and has played a key role in the development of many new compounds and pharmaceuticals..

Example

One example of the Béchamp reaction is the synthesis of para-nitrophenylarsonic acid from para-nitrophenol and arsenic acid. The reaction is typically performed at 150-200 °C in the presence of a catalyst, such as sulfuric acid..

The reaction can be represented by the following equation:

para-nitrophenol + As2O5 → para-nitrophenylarsonic acid + H2O

In this reaction, the para-nitrophenol acts as the aromatic amine or phenol, and the As2O5 acts as the arsenic acid. The reaction proceeds by condensation of the para-nitrophenol with the As2O5 to form the para-nitrophenylarsonic acid. The reaction is typically performed in a high-pressure reactor and takes several hours to complete..

Mechanism of reaction

The Béchamp reaction mechanism is a two-step process. The first step is the formation of an intermediate, an arsine, by the reaction of an arylamine or phenol with As2O5. The second step is the hydrolysis of the intermediate to form the arylarsonic acid..

  • Step 1 – Formation of arsine intermediate: The first step of the Béchamp reaction is the formation of an arsine intermediate by the reaction of an arylamine or phenol with As2O5. The arylamine or phenol acts as a nucleophile and attacks the As=O bond of As2O5. This results in the formation of an arsine intermediate and the release of H2O..
  • Step 2 – Hydrolysis of arsine intermediate: The second step of the Béchamp reaction is the hydrolysis of the arsine intermediate. Hydrochloric acid or sulfuric acid acts as a catalyst and protonates the nitrogen atom of the arsine intermediate. This causes the nitrogen atom to release the leaving group, which is an HCl or H2SO4 molecule. This results in the formation of arylarsonic acid and the release of an arsine molecule (AsH3)..

Overall the reaction can be summarized by the following equation:

Arylamine or phenol + As2O5 → Arylarsonic acid + AsH3

References

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