Leuckart reaction
The Leuckart reaction is the chemical reaction that converts aldehydes or ketones to amines. The reaction is an example of reductive amination. The reaction, named after Rudolf Leuckart, uses either ammonium formate or formamide as the nitrogen donor and reducing agent. It requires high temperatures, usually between 120 and 130 °C; for the formamide variant, the temperature can be greater than 165 °C.
History
The Leuckart reaction is named in honor of its developer, the German chemist Rudolf Leuckart. He discovered that heating benzaldehyde with formamide does not produce benzylidenediformamide as anticipated, but benzylamine. In 1891, a colleague of Leuckart at the University of Göttingen, Otto Wallach, performed further reactions using alicyclic and terpenoid ketones as well as aldehydes, demonstrating the general application. Over the course of the past century, chemists have discovered several methods to improve the yield of the reaction and carry it out under less strenuous conditions. Pollard and Young summarized various ways in which amines can be formed: using either formamide or ammonium formate, or both, or adding formic acid to formamide. However, using just ammonium formate as the reagent produces the best yields. Using formamide produces low yields compared to ammonium formate but yields can be increased by using large amount of formamide, or using ammonium formate, ammonium sulfate, and magnesium chloride as catalysts.Mechanism
Ammonium formate as reagent
Ammonium formate is a source of formic acid and ammonia. Starting with nucleophilic attack on the carbonyl by the ammonia, the carbonyl is converted to the iminium ion:The iminium is then reduced by the formate: