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Reaction of a wide range of nitrones (I) with pyrazolin-5-one (II) using silicotungstic acid as catalyst gives unexpectedly bis(pyrazolyl)methanes (III) instead of expected addition products.

A three-dimensional network of crystalline WO3 nanowires is prepared by impregnation of a three-dimensional SBA-15 silica template with a solution of silicotungstic acid in EtOH for 6 h at room temperature followed by mineralization (300 °C for 1 h in air and 600 °C for 4 h in air) and template removal (HF solution, 20 °C, 6 h).

A silver tungstate salt is used as an efficient and reusable heterogeneous catalyst for the conversion of terminal alkynes (Ig) into corresponding ketones (II).

The condensation of acetophenones with aldehydes proceeds highly chemoselective under neat conditions to yield the title compounds (III) as exclusive (E) isomers.

A simple and efficient catalytic protocol for the synthesis of 14-aryl-14 H -dibenzo[a,j]xanthenes via the one-pot condensation of β -naphthol and aryl aldehydes using silicotungstic acid (H 4 [SiW 12 O 40 ]) is reported. The present method offers several advantages such as high to excellent yields, short reaction times, recovery and reusability of catalyst, mild reaction conditions and easy workup procedures.

The authors have shown that electrochemical methodology can be extended to the investigation of the protonically conducting, crystalline mixed-valence molecular materials. Such studies provide information about thermodynamics and kinetics of redox processes in these materials. Additional results, with thin films and powders of silicotungstic acid and related oxide systems, clearly suggest that solid-state electrochemical responses are very sensitive to the degree of hydration, which probably controls the protonic mobility. They have been able to perform useful solid-state electrochemical measurements on other powdered materials, including Prussian blue analogues and metalloproteins, by essentially the same methodology.

A new chemical deposition method has been developed to prepare photoconducting n-Sb 2 S 3 thin polycrystalline films. The solution composition of the deposition bath was 0.025M potassium antimonyl tartarate, 0.4M triethanolamine, 0.025M thioacetamide, and 5×10 -7 M silicotungstic acid (STA), respectively. The as-deposited and the annealed films were characterized through x-ray diffraction, neutron activation analysis, and the optical absorption investigations. The photoelectrochemical performances of these films were examined

Recent progresses in practical applications of (i) supported heteropolyacid and (ii) Pd/perovskite catalysts are described. (i) Two industrial catalytic processes, ethyl acetate and acetic acid syntheses both from ethylene, utilize silicotungstic acid, alone and together with Pd, respectively, carefully supported on silica, and exhibit high performance from green chemical and economical viewpoints. The layer structure of heteropolyacid on silica and physical properties of silica are among the key factors of the high performance. (ii) Pd/perovskite catalyst is applied for the treatment of automotive emission, where the catalyst life is very much elongated by embedding Pd into the perovskite lattice and hence resulted in much reduced usage of Pd. These are good examples of green catalytic technology that will contribute to the sustainable society.

H 4 SiW 12 O 40 ·xH 2 O catalyzed the one-pot three component condensation reactions of aldehydes, 1,3-dicarbonyl compounds and urea in refluxing acetic acid leading to 3,4-dihydropyrimidin-2(1H)-one in high yields.

Using a Microscal flow microcalorimeter, integral sorption and desorption enthalpies of ammonia on silicotungstic acid H4SiW12O40 dehydrated at 433 K and 483 K were determined. The quantitative coverage determination enabled us to estimate the amounts of the irreversibly as well as (much smaller) reversibly bonded ammonia at its equilibrium state in the gas phase (pNH3 = 1.01 kPa). It has been shown that irreversible sorption at 373 K results in the formation of NH4+ ions while at 298 K two NH3 molecules are adsorbed per one proton in heteropolyacids. This suggests the formation of an NH4+·NH3 adduct which is also present in N2H7I, the only known solid salt of a diammonium ion.

As part of a study of hydrogen transfer reactions over alumina, the reactions of acetophenone with methanol over η-alumina at 300–500 °C were studied. In addition to styrene arising from reductive dehydration, products arising from methylation (propiophenone, β-methylstyrene) were also observed. At higher conversion, secondary reactions like dealkylation of higher ketones and alkylation, dealkylation, and hydrogenation of olefins were also observed. Reactions have also been carried out with modified alumina (fluorided and Na+-doped) catalysts, HY-zeolite, phosphotungstic acid, and silicotungstic acid to study the effect of acidity on the selectivity for these reactions. Reactions of methanol with aralkyl ketones and with olefins were also studied. Acetophenone conversion was found to increase with increasing catalyst basicity while the selectivity for reductive dehydration decreased. Conclusions have also been drawn, on the basis of these studies, regarding the nature of the active catalytic sites responsible for the different reactions and mechanisms have been proposed for the surface reactions.