Plasmon Mediated Catalytic Oxidation of sec-Phenethyl and Benzyl Alcohols

JAZMÍN SILVERO; GENIECE L. HALLETT-TAPLEY; MARÍA GONZÁLEZ-BÉJAR; JOSÉ CARLOS NETTO-FERREIRA; JUAN C. SCAIANO

Congreso; 21ST I-APS CONFERENCE? (Congreso XXI de la Asociación Internacional de Fotoquímica; 2011

Plasmon Mediated Catalytic Oxidation of sec-Phenethyl and Benzyl Alcohols Jazmín Silvero, Geniece L. Hallett-Tapley, María González-Béjar, José Carlos Netto-Ferreira, and Juan C. Scaiano* Centre for Catalysis Research and Innovation, Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa K1N 6N5, Canada In organic and industrial chemistry, alcohol oxidations are one of the most widely exploited reactions due to the extensive use of ketones in the manufacturing of various products, such as paints and plastics. Conventional methods of oxidizing benzylic alcohols involve the use of chromates or permanganates, typically viewed as environmentally unfriendly oxidants; therefore current interests focus on the development of greener catalysts that efficiently oxidize these chemicals as effectively as the more traditional methods, while still offering high selectivity and the advantage of catalyst reusability and less toxic waste. Metalic nanoparticles (NPs) seem to have a lot to offer in this field. In particular, AuNPs have shown interesting properties. In the present work we use AuNP in aqueous solutions, obtained from reduction of Au3+ by photochemically generated ketyl radicals. The absorption of energy at 530 nm -the surface plasmon bland (SPB) for spherical AuNPs- results in a collective oscillation of the surface electrons of the AuNP. This methodology has been previously used to excite nearby molecules, also known as a transmitter/receiver antenna effect. Moreover, the intermediate polarization of the NP surface electron via plasmon excitation can create rapid, localized heating of the NP surface allowing for harvesting of thermal energy. The dramatic increase in temperature within close proximity to the NP allows chemical reactions typically requiring high temperatures to be carried out in the microenvironment surrounding the AuNP at ambient bulk temperatures. This effect is known as plasmon mediated catalysis (PMC). In the present contribution, PMC is employed to successfully oxidize sec-phenethyl and benzyl alcohols in the presence of aqueous AuNP and H2O2 using laser drop techniques or light emitting diodes; the results are compared with microwave excitation. In all cases, good conversion to the corresponding ketone or aldehyde was observed (Table 1). A mechanism involving both photothermal and photochemical effects will be discussed. Table 1. Results of PMC of alcohol oxidation (% of ketone or aldehyde)