Phosphotungstic acid catalyst

HIGHLY ACTIVE SILICA SUPPORTED PHOSPHOTUNGSTIC ACID CATALYST FOR ACYLATION REACTIONS... 

Highly active silica supported phosphotungstic acid catalyst 223... 

In this work, various Ru-BINAP catalysts immobilized on the phosphotungstic acid(PTA) modified alumina were prepared and the effects of the reaction variables (temperature, H2 pressure, solvent and content of triethylamine) on the catalytic performance of the prepared catalysts were investigated in the asymmetric hydrogenation of dimethyl itaconate (DMIT). 

The preparation of this type of catalyst is quite simple. HPAs such as phos-photungstic acid were adsorbed onto inorganic supports such as clays, alumina, and active carbon. Subsequently, the metal complex was added to form the immobilized catalyst. If necessary, the catalyst can be pre-reduced. These types of catalysts were developed mainly for enantioselective hydrogenations. For instance, a supported chiral catalyst that was based on a cationic Rh(DIPAMP) complex, phosphotungstic acid and alumina showed an ee-value of 93% with a TOF of about 100 IT1 in the hydrogenation of 2-acetamidoacrylic acid methyl ester (Fig. 42.4 Table 42.2). 

To examine the effect on the catalysis of the anion of the metal complex, Brandts [96] immobilized the two different catalyst precursor complexes [Rh(COD)2]BE4 and [Rh(COD)Cl]2 on phosphotungstic acid-modified alumina to form 7-AI2O3/... 

Sulfated zirconia catalysts showed selectivities comparable to those of AICI3 in the alkylation of benzene with 1-alkenes to linear alkylbenzenes.396 The mesopor-ous sulfated zirconia sample could be regenerated by solvent extraction or thermal treatment. Phosphotungstic acid supported on sulfated zirconia doped with Fe proved to be very active and highly selective in the alkylation of benzene with propylene at 100-150°C to produce cumene both monoalkylation and cumene formation have better than 90% selectivity.397 It can be regenerated at moderate temperature (350°C). 

The solid acid catalyzed adamantylation of substituted benzene derivatives was studied with the aim to achieve high para regioselectivities. Of various acidic resins, zeolite HY, sulfated zirconia, perfluorolkanesulfonic acids, and phosphotungstic acid, Amberlyst XN-1010 was found to be the catalyst of choice to afford para-substituted alkylbenzenes with selectivities exceeding 70%.398 In further systematic studies with a Nafion-H-silica nanocomposite catalyst,399 and various... 

The problem of heavy metal contamination of effluent streams which can result from the use of homogeneous catalysts, whilst not insurmountable, can be eliminated by the use of heterogeneous catalysts such as titanium silicalite205 and phosphotungstic acid on alumina206 with hydrogen peroxide as the primary oxidant. 

The following catalyst preparations are described phosphotungstic acid on y-aiumina, ammonium molybdate on a cross-linked polystyrene anionic exchange resin, metal(IV) phosphates, and chromium silicalite. 

Phosphotungstic acid (3 g) was dissolved in demineralized water (25 ml). To this solution was added y-alumina (20 g), and the mixture stirred at ambient for 4 h. The slurry, was then filtered at the pump, and the residue dried in an oven at 60 °C for 18 h. The air dried solid was then calcined at 500 °C for 4 h. in a muffle furnace. The catalyst produced had a nominal polyoxometalate loading of 10 % w/w. 

Penicilin-G (4 g, 10.8 mmol), water (40 ml), and the catalyst ((NH4)eMo7024-A26) (0.5 g) were charged to a three necked flask, fitted with, thermometer, cooling bath, overhead stirrer, and peristaltic pump, was equilibrated to 20 °C. H2O2 (35 % w/w. 1.04 g, 10.8 mmol) was added via the pump over 45 mins. On completion of the H2O2 addition, the reaction was maintained under these conditions for a further 45 mins. Analysis of the reaction was via H.P.L.C. and comparison to the authentic compound. Benzenethiol was also oxidized using phosphotungstic acid on alumina. However, the solvent was t-butanol, and the reaction temperature was 80 °C for 4 h. 

Epoxidation processes currently account for around 30 % of H2O2 consumption in the chemical industry. Present processes are mainly peracid based and have limitations in scope and safety, as well as incurring high capital investment. Consequently, we have attempted to develop heterogeneous catalyst systems for such transformations. A system which has been extensively studied has been the epoxidation of cyclic aikenes with H2O2 in the presence of supported phosphotungstic acid. Table 3 illustrates our results. 

As can be seen from the results the order of reactivity was cyclic aikenes greater than linear aikenes. The order is the expected one, and illustrates that the substrate had no difficulty in reaching the catalytically active sites on the solid surface. The immobilized phosphotungstic acid material complements a titanium silicalite type (TS-1) catalyst, which is much more effective towards the epoxidation of linear aikenes in the presence of aqueous H2O2, and particularly... 

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