K5PW11NiO39‐catalyzed oxidation of benzyl alcohol with hydrogen peroxide

• Published in: ChemistrySelect (Weinheim) 2019-01, Vol.4 (1), p.302-310
• Main Authors: Coronel, Nelson C., da Silva, Márcio J., Ferreira, Sukarno O., da Silva, Rene C., Natalino, Ricardo
• Format: Article
• Language: English
• Subjects: benzyl alcohol; catalytic oxidation; hydrogen peroxide; metal-substituted Keggin heteropolyacid salts
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.201802616

In this work, we synthesized a series of metal‐substituted potassium heteropolyacid salts and investigated its catalytic activity on oxidation of benzyl alcohol with H2O2 under homogeneous (CH3CN) and biphasic (toluene/water) conditions. The Keggin heteropolyacids were converted to lacunar salts (i. e., K7PW11O39; K7PMo11O39 and K8SiW11O39), which had their vacancies filled with metal cations (i. e., Al3+, Fe3+, Co2+, Cu2+, and Ni2+), generating the metal‐substituted salts. The K5PW11NiO39 proved to be the most efficient catalyst. The synergic effect raised between the PW11O397− anion and Ni2+ cation improved the redox properties and the activity of the catalyst. The K5PW11NiO39 catalyst was able to promote the benzyl alcohol oxidation with hydrogen peroxide in biphasic conditions in the absence of phase transfer catalyst. Benzaldehyde and benzoic acid were the main products. The effects of main reaction parameters were assessed. The K5PW11NiO39 catalyst was successfully recovered and reused without losing activity. An attractive and environmentally oxidative process based on metal substituted lacunar salt catalysts was developed. The metal substituted Keggin heteropolyacid salts (i. e., M=Fe3+, Al3+, Co2+, Ni2+ and Cu2+) were evaluated as solid catalysts on benzylic alcohol oxidation to benzaldehyde. Among metal‐substituted heteropolyacid salts evaluated, K7PW11NiO39 was the most active and selective.