Abstract
Preyssler's anion, with formula [NaP5W30O110]14-, catalyzes the oxidation of aromatic aldehydes to related carboxylic acids by hydrogen peroxide as oxidizing agent, under microwave irradiation, or at 70 ºC. Both homogeneous and heterogeneous Preyssler's catalysts (as H14[NaP5W30O110 ]) were used and had their activity compared with those of some Keggin structures. Our data indicate that Sodium30-tungsto pentaphosphate, the so-called Preyssler's anion, with high hydrolytic (pH=0-12) and thermal stability is the best catalyst with high yield and good selectivity. Under microwave irradiation, this polyanion supported on SiO2 was found to be an excellent catalyst for aldehydes with low loss factor in 1-2 min (the loss factor is a measure of the ability of the material to dissipate energy). The effects of various parameters, including catalyst type, nature of the substituent in the aldehyde and temperature, on the yield of the carboxylic acids were studied.
Highlights
Catalysis by solid acid catalysts and related compounds is a field of increasing importance
We show that the silica-supported Preyssler’s catalyst, in solventfree conditions, renders effective the aldehyde oxidation to carboxylic acid in the presence of hydrogen peroxide under microwave irradiation, in 1-2 min
The catalysts with different initial H14[NaP5W30O110] loadings on silica were prepared for the oxidation of benzaldehydes to carboxylic acids under microwave irradiation
Summary
Catalysis by solid acid catalysts and related compounds is a field of increasing importance. Oxidation of benzaldehydes to related carboxylic acids is important and has been studied by many researchers.[13] Mizuno and coworkers examined the oxidation of octanal by O2 with heteropolyacids including nickel and iron.[14] Ishii and coworkers reported oxidation of aldehydes to carboxylic acids catalyzed by transition metal-substituted heteropolyacids.[15] Zamaraev and coworkers reported the catalytic properties of some salts of Keggin heteropolyacids including cobalt.[16] most of the works have dealt with metal-substituted heteropolyanions with Keggin structures, no catalytic activity has been reported for Preyssler’s anion. After cooling to room temperature and filtering of the mixture, the procedure was the same as above
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