Baudisch reaction

What is Baudisch reaction?

The Baudisch Reaction, reported by Baudisch in 1939, involves the synthesis of o-nitrosophenols from benzene or its derivatives, hydroxylamine, and hydrogen peroxide in the presence of copper salts. Unlike conventional nitrosation of phenol with HNO2, the Baudisch reaction introduces the nitroso and hydroxyl groups simultaneously into the adjacent position on the aromatic nucleus, resulting in reddish violet copper salts. Other metal salts, such as Ni2+ and Fe2+, can also be used in this reaction.

Baudisch reaction
Baudisch reaction

R = alkyl, phenyl, CI, Br, NO2, etc.

Copper salts are necessary to stabilize the nitrosyl radical and form stable complexes, which prevent further oxidation of o-nitrosophenols to o-nitrophenols or rearrangement to p-quinone monoximes.

The o-nitrosophenols obtained from the reaction are volatile due to the formation of intramolecular hydrogen bonding and can be obtained by acidifying the complexes with HCl, followed by extraction in petroleum ether.

The reaction is not applicable to aromatic aldehydes and primary amines, as the aldehyde group will react with the nitrosyl radical or hydroxylamine to form hydroxamic acid or oxime, and primary amine will react with the nitrosyl radical to form diazo compounds.

The reaction can be applied to phenols instead of non-hydroxyl benzene derivatives and produces similar products with higher yields in a shorter reaction period due to the higher solubility of phenols in water.