One-pot Synthesis of Benzil Derivatives from Aromatic Aldehydes

One-pot benzoin condensation and air oxidation of some aromatic aldehydes were investigated. All the reactions were carried out by catalytic effect of cyanide ion in alcoholic solvents under atmospheric O2. Under these conditions, 4-methoxybenzaldehyde, 4-bromobenzaldehyde, 3-nitrobenzaldehyde and 2-furylcarbaldehyde transformed to their relative benzil derivatives, directly. But the procedure was not successful with 4-methylbenzaldehyde, 4-chlorobenzaldehyde, 2-pyridinecarbaldehyde and 4-pyridinecarbaldehyde. The later compounds were converted to their relative benzoin or pyridoin derivatives. The so-formed benzoins were then oxidized to their corresponding benzil derivatives using a mixture of ammonium nitrate and cupric acetate in 80% aqueous solution of acetic acid. However, pyridoines converted to blue complexes in the same reaction conditions.