Sunshine D. Kurbah, Arvind Kumar, Sankey Shangpung, Mrityunjaya Asthana, Ibanphylla Syiemlieh and Ram A. Lal Pages 62 - 68 ( 7 )
Background: The oxidation of alcohols to afford carbonyl compounds is a key transformation in organic chemistry. Significant development has occurred in the recent years, in catalytic oxidation of alcohols by aerial oxygen. However, the alcohol oxidation mediated by H2O2 is quite meagre. From economic and environmental point of views, the oxidation of alcohols mediated by H2O2 is quite attractive in particular.
Methods: Various alcohols Cu3(slmh)( µ-Cl)2(CH3OH)3].0.5CH3OH, ligand, H2O2, CDCl3, Tetramethylsilane were used for oxidation of alcohols to carbonyl compounds. For analysis, IR, 1H NMR, and 13C NMR were utilized.
Results: Taking benzyl alcohol as a model compound, first reaction conditions were optimized. The combination of catalyst (0.04 mmol, 0.032 mg), 15% H2O2 (8.83 mmol, 2 mL) at 70°C under solvent free condition was found to be the most appropriate condition for the oxidation of alcohols. The efficiency of the catalyst was tested by oxidizing several aromatic ring substituted benzyllic, aliphatic and allylic alcohols by H2O2. We efficiently carried out oxidation of nineteen alcohols. The benzyl alcohols bearing electron withdrawing groups gave excellent yield of the corresponding carbonyl compounds whereas those bearing electron donating substituent gave slightly lower conversions. The heteroaroyl alcohols also gave excellent yield. The hydroxy group was oxidized selectively to aldehyde in cinnamyl alcohol keeping double bond intact. Secondary alcohols such as cyclohexane and 1-phenylethanol were negligibly oxidized. The aliphatic alcohols gave much lower yield as compared to benzyllic and allylic alcohols.
Conclusion: The benzyllic, aliphatic and allylic alcohols were effectively oxidized to aldehydes by hydrogen peroxide using catalytic amount of Cu3(slmh)( µ-Cl)2(CH3OH)3].0.5CH3OH. The process is simple and mild, the catalyst can be recycled to get improved catalytic activity.
Catalysts, Oxidation, alcohols, carbonyl compounds, [Cu3(slmh)( µ-Cl)2(CH3OH)3].0.5CH3OH, hydrogen peroxide, spectroscopic study.
Centre for Advanced Studies, Department of Chemistry, North-Eastern Hill University, Shillong-793022, India.