Copper catalyzed oxidation of benzylic alcohols in water with H sub(2)O sub(2)

• Published in: Applied catalysis. A, General Vol. 411-412; pp. 180 - 187
• Main Authors: Ahmad, Jahir Uddin, Raeisaenen, Minna T, Leskelae, Markku, Repo, Timo
• Format: Journal Article
• Language: English
• Published: 16.01.2012
• Subjects: Alcohols; Aldehydes; Catalysts; Copper; Ligands; Oxidation; Recycled; Selectivity
• ISSN: 0926-860X
• DOI: 10.1016/j.apcata.2011.10.038

A straightforward, efficient and sustainable copper catalyzed method was developed for oxidation of benzylic alcohols with 30% H sub(2)O sub(2) in water. The reaction proceeded with CuSO sub(4) catalyst (1 mol%) at 100 degree C without additional base or ligand. Primary benzylic alcohols were converted almost quantitatively to aldehydes with 70-90% selectivity, corresponding acids being the major side products. Also secondary benzylic alcohols afforded the corresponding ketones in high conversion with selectivities greater than 90%. It was demonstrated that the CuSO sub(4) catalyst can be recycled and reused at least for three runs, even though with some loss of catalytic activity. Selectivity of the CuSO sub(4) based catalyst system could be further increased by using 2-N-(p-fluorophenyl)-pyrrolecarbaldimine (1) as a ligand in combination with TEMPO in K sub(2)CO sub(3) solution. The catalyst system was individually optimized (1 mol% CuSO sub(4), 2 mol% 1, 0.1 M K sub(2)CO sub(3) and 5 mol% TEMPO) for a wide range of benzylic and allylic alcohols, which were quantitatively and selectively converted into the corresponding aldehydes with 3 eq. of H sub(2)O sub(2) in 1 h.