Kolbe–Schmitt reaction

A chemical reaction used in organic chemistry

The Kolbe–Schmitt reaction is an important chemical reaction in organic chemistry that involves the carboxylation of phenolates to produce salicylic acid derivatives. This reaction is named after the chemists Hermann Kolbe and Rudolf Schmitt, who developed the process in the late 19th century.

Mechanism

The Kolbe–Schmitt reaction proceeds through the reaction of a sodium phenoxide with carbon dioxide under high pressure and temperature conditions. The general mechanism involves the following steps:

1. Formation of Sodium Phenoxide: Phenol is treated with sodium hydroxide to form sodium phenoxide.
2. Carboxylation: The sodium phenoxide is then exposed to carbon dioxide gas at elevated temperatures (around 125–150 °C) and pressures (approximately 100 atm). This results in the formation of an ortho-carboxylate intermediate.
3. Acidification: The reaction mixture is acidified, typically with sulfuric acid, to yield the desired salicylic acid.

File:Kolbe-Schmitt reaction mechanism.png

Mechanism of the Kolbe–Schmitt reaction.

Applications

The primary application of the Kolbe–Schmitt reaction is in the industrial production of salicylic acid, which is a precursor to aspirin and other pharmaceuticals. Salicylic acid is also used in the manufacture of dyes, preservatives, and as a keratolytic agent in dermatology.

Advantages and Limitations

The Kolbe–Schmitt reaction is advantageous due to its ability to selectively carboxylate phenolates at the ortho position. However, the reaction requires harsh conditions, including high temperatures and pressures, which can limit its applicability in some contexts. Additionally, the reaction is specific to phenolates and does not work well with other types of aromatic compounds.

Historical Context

The development of the Kolbe–Schmitt reaction marked a significant advancement in the field of organic synthesis. Hermann Kolbe first discovered the reaction in 1860, and it was later refined by Rudolf Schmitt in 1885. This reaction laid the groundwork for the synthesis of many important aromatic carboxylic acids.

Related pages

• Salicylic acid
• Aspirin
• Carboxylation
• Phenol
• Organic chemistry