Doped Keggin heteropolyacids as catalysts in sulfide oxidation and dihydropyrimidinone synthesis

PATRICIA VÁZQUEZ; VALERIA PALERMO; GABRIEL SATHICQ; HORACIO THOMAS; GUSTAVO ROMANELLI

San Juan

Congreso; 43rd IUPAC World Chemistry Congress of 2011; 2011

Colegio de Químicos de Puerto Rico (CQPR) and the International Union of Pure and Applied Chemistry (IUPAC)

Bulk heteropolyacids (HPAs) with Keggin structure are well known as oxidation and acidcatalysts in which the redox and acid-based properties can be tuned by variation of thecentral heteroatom and/or addenda transition metal-substituted atoms. In this research, wereport the preparation of V, Bi and Bi-V Keggin structures where Mo is partially replace byV, Bi, and Bi and V, respectively (H4PMo11VO40, (PMoV); H6PMo11BiO40, (PMoBi); andH5PMo11V0.5Bi0.5O40, (PMoVBi), in H3PMo12O40, (PMo)). These catalysts were wellcharacterized by means of 31P-NMR, UV-visible spectra, FT-IR spectra, thermal analysis,textural properties and potentiometric titration. Mo, V and Bi amounts were estimated byICP-AES analysis. In addition, the activities of the synthesized catalysts were evaluated inthe selective oxidation of sulfides to sulfoxides/sulfones and in the solvent-freemulticomponent synthesis of dihydropyrimidinones by the Biginelli method. Theincorporation of V, Bi and Bi-V into the structure of PMo increases the catalytic activity(acid and redox catalysts). The correlation between catalytic oxidation performance (sulfideoxidation) and absorption edge energies of HPA catalysts demonstrated that the absorptionedge energies could be utilized as a correlation parameter for the reduction potentials(oxidizing powers) of the HPA catalysts, and furthermore, as a probe of the catalyticoxidation performance of HPA catalysts. The two most active catalysts (PMoV andPMoVBi) were supported on aminopropyl-functionalized silica (SiO2NH2). The catalystswere prepared by the equilibrium adsorption technique. They were found to be efficient,ecofriendly and recyclable heterogeneous catalysts for the selective oxidation ofdiphenylsulfide to the corresponding sulfoxide/sulfone, under mild reaction conditionsusing aqueous hydrogen peroxide as the oxidant.For the Biginelli synthesis, a correlation between the yields of the dihydropyrimidinonesand the acidic site amount of the catalysts was observed: PMoBiV > PMoV > PMoBi >PMo. All catalysts can be recycled without loss of the catalytic activity.