Direct Oxidative Conversion of Benzoyl Chlorides to 2-Imidazoles Using Heteropolyacids

The reaction of benzoyl chlorides with ethylenediamine in the presence of catalytic amounts of Keggin-type heteropolyacids led to oxidative conversion of benzoyl chlorides to the corresponding 2-imidazoles in good yields.     

One‐Pot Synthesis of 2‐Arylbenzoxazoles Promoted by Heteropolyacids

Benzoxazole derivatives were obtained in high yields with excellent purity from the condensation of 2‐aminophenol with benzaldehydes and benzoic acids in the presence of a catalytic amount of heteropolyacids (HPAs).     

A direct oxidative route for the synthesis of pyrimidines using heteropolyacids

Pyrimidines are synthesized via a direct oxidative one-pot, three-component, reaction between 1,3-diketone, benzaldehydes, and ammonium acetate in the presence of catalytic amounts of Keggin-type heteropolyacids under refluxing conditions in good yields.     

Hydroformylation of alkyl alkenes catalyzed by rhodium supported on MCM-41: The effect of H3PW12O40 on the catalytic activity and recycling

Heteropolyacids impregnated with rhodium(I) or (III) complexes were prepared and used as supported catalysts in the hydroformylation of alkyl alkenes. Two general types of catalysts were prepared and tested: rhodium(I) or (III) in the presence and in the absence of the heteropolyacid H₃PW₁₂O₄₀, 25H₂O (adopted as HPW₁₂) supported on MCM-41 (30 Å). 1-Octene was chosen as a model substrate. Different types of supported catalysts were tested in the hydroformylation of 1-octene and other alkyl alkenes. The effects of the temperature and the type of solvent on the reaction were studied. The results showed that the supported catalysts containing the heteropolyacid H₃PW₁₂O₄₀, 25H₂O (HPW₁₂) along with rhodium(I) or (III) gave higher catalytic activity. In addition, the recycling of the supported catalysts was studied and the results showed again the important effect of the presence of HPW₁₂ on the recycling of the rhodium catalysts.     

Synthesis and physicochemical properties of Zr-MCM-41 mesoporous molecular sieves and Pt/H3PW12O40/Zr-MCM-41 catalysts

For the first time, modifications of the surface and framework of Si-MCM-41 by depositing a heteropolyacid on the surface and by introducing foreign Zr⁴⁺ ions into the framework are investigated. The Zr-modified Si-MCM-41 mesoporous materials (hereafter referred as WSZn, n=Si/Zr=25, 15, 8, 4) were synthesized through a surfactant-templated preparation approach, using low-cost fumed silica as the Si precursor. After impregnation with 25 wt% of H₃PW₁₂O₄₀, the surface Brönsted acidity of the Pt/H₃PW₁₂O₄₀/WSZn catalysts was greatly enhanced by 2-10 times relative to the bare WSZn support. Two kinds of supported heteropolyacids were formed: (i) bulk-like heteropolyacid crystals with unchanged Keggin structures, and (ii) highly dispersed heteropolyacid with distorted Keggin units. The formation of various kinds of heteropolyacid structures is closely related to the interaction between the heteropolyanions and the hydroxyl groups in the host support.     

杂多酸的固载化研究(II)

研究了以多种方法化学改性的不同活性炭表面化学特性及十二硅钨酸（SiW_(12)）在相应表面的吸附. 首次提出，不同原料来源和改性的活性炭对SiW_(12)的吸附有不同的等温线形式和吸附力. 活性炭表面的羰基有利于SiW_(12)的吸附，而表面的羧基则是不利的．     

Rapid and efficient synthesis of 4(3H)-quinazolinones under ultra sonic irradiation using silica-supported Preyssler nano particles

A new synthesis of 4(3H)-quinazolinone from the reaction of 2-amino-benzamide, and acylchlorides in the presence of catalytic amounts of silica-supported Preyssler nano particles as green, reusable and efficient catalyst under ultra sonic irradiation is reported.     

Synthesis of 1,8-dioxooctahydroxanthenes utilizing PMA-SiO_2 as an efficient reusable catalyst

PMA-SiO2 has been utilized as an efficient catalyst system in preparation of 1,8-dioxooctahydroxanthenes.     

Electro-oxidation of CO on Pd black in phosphotungstic acid

Electro-oxidation of CO by Pd black in phosphotungstic acid (PWA) has been studied on porous gas-diffusion electrodes. Galvanostatic steady-state polarization data show that the reaction proceeds under strong activation control at low current densities. The current density at 0.5 V_NHE is found to be three times higher than that in a H₂SO₄ reference electrolyte. X-ray photoelectron spectroscopic data on various electrochemically tested electrodes show lower oxidized Pd species in PWA than in H₂SO₄. It is conjectured that an increase in the electron density around Pd sites is ameliorated by PWA in relation to H₂SO_4, with a consequent promoting effect of the heteropolyacid towards CO electro-oxidation. Received: 29 July 1998 / Accepted: 15 September 1998     

Comparison of H3PW12O40 and H4SiW12O40 heteropolyacids supported on silica by H MAS NMR

The H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀ heteropolyacids supported on silica were studied by ¹H MAS NMR as a function of both the coverage and the dehydroxylation temperature. The signal at ca. 8 ppm attributed to the highly acidic protons of the anhydrous form of the heteropolyacid was never observed in the case of the phosphotungstic polyanion supported on silica while it was clearly present in the case of the silicotungstic species. These results explain the different activities of the two supported heteropolyacids in acid reactions involving strong acid sites. To cite this article: A. Thomas et al., C. R. Chimie 8 (2005).