Alkylation catalysts heteropolyacids

Cesium salts of 12-tungstophosphoric acid have been compared to the pure acid and to a sulfated zirconia sample for isobutane/1-butene alkylation at room temperature. The salt was found to be much more active than either the acid or sulfated zirconia (201). Heteropolyacids have also been supported on sulfated zirconia catalysts. The combination was found to be superior to heteropolyacid supported on pure zirconia and on zirconia and other supports that had been treated with a variety of mineral acids (202). Solutions of heteropolyacids (containing phosphorus or silicon) in acetic acid were tested as alkylation catalysts at 323 K by Zhao et al. (203). The system was sensitive to the heteropoly acid/acetic acid ratio and the amount of crystalline water. As observed in the alkylation with conventional liquid acids, a polymer was formed, which enhanced the catalytic activity. 

Friedel-Crafts alkylations are among the most important reactions in organic synthesis. Solid acid catalysts have advantages in ease of product recovery, reduced waste streams, and reduction in corrosion and toxicity. In the past, people have used (pillared) clays (18), heteropolyacids (19) and zeohtes (20) for Friedel-Craft alkylations, with mixed success. Problems included poor catalyst stabihty and low activity. Benzylation of benzene using benzyl chloride is interesting for the preparation of substitutes of polychlorobenzene in the apphcation of dielectrics. The performance of Si-TUD-1 with different heteroatoms (Fe, Ga, Sn and Ti) was evaluated, and different levels of Fe inside Si-TUD-1 (denoted Fei, Fe2, Fes and Feio) were evaluated (21). The synthesis procedure of these materials was described in detail elsewhere (22). 

Since S03/H2S04 is clearly not the most desirable system for industrial applications, a formidable challenge is to find an oxidant that oxidizes Pt(II) much faster than S03 does, operates in an environmentally friendly solvent, and can be (like SVI/SIV) reoxidized by oxygen from air. Ideally, the reduced oxidant would get reoxidized in a continuous process, such that the oxidant acts as a redox mediator. In addition, the redox behavior has to be tuned such that the platinum(II) alkyl intermediate would be oxidized but the platinum(II) catalyst would not be completely oxidized. Such a system that efficiently transfers oxidation equivalents from oxygen to Pt(II) would be highly desirable. A redox mediator system based on heteropolyacids has been reported for the Pt-catalyzed oxidation of C-H bonds by 02, using Na8HPMo6V6O40... 

Friedel-Crafts alkylation processes were traditionally operated at 65-70°C with AICI3 and at 40-60°C with HF. A variety of solid acid catalysts have been developed at the laboratory level, mainly based on zeolites, heteropolyacids or sulfated zirconia (zirconia treated with sulfuric acid). The most recent industrial achievement is the Detal process (UOP-CEPSA) which is based on silica-alumina impregnated with HF. The selectivity towards linear alkylbenzenes exceeds 95%. The cymene processes use AICI3 in the liquid phase or supported phosphoric acid as catalysts. 

Zeolites (6,7), heteropolyacids (8,9), sulfated zirconia (10,11), and other materials (12) have already been explored. All of these materials deactivate in a rather short time, ranged in the order of minutes to hours, and therefore any process involving solid acid catalysts for isobutane alkylation would require frequent regenerations. 

Solid acids would be attractive, and an intermediate step has been the use of heteropolyacids as catalysts for the preparing alkyl glycosides [26]. 

Blasco, T., Corma,A., Martinez, A., and Martinez-Escolano, P. 1998. Supported heteropolyacid (HPW) catalysts for the continuous alkylation of isobutane with 2-butene the benefit of using MCM-41 with larger pore diameters. 

Keywords Oleic acid alkyl esters, biodiesel, heteropolyacids, tin catalysts, esterification, homogeneous and heterogeneous catalysis... 

In an attempt to combine acidity, stability, and easy catalyst regeneration, other solid acid catalysts, among which zeolites have been of particular interest, have been looked to. The following part of this article reviews some of the alkylation works carried out using zeolites as well as other solids with stronger acidities such as sulfated transition metal oxides and heteropolyacids (HPAs) and related compounds. 

Mizuno N, Misono M (1998) Heterogeneous eatalysis. Chem Rev 98 199-218 Briand LE, Baronelti LE, Thomas HJ (2003) The state ofthe artonWells-Dawson heteropoly-compounds a review of their properties and applications. J Mol Catal A Gen 256 37-50 Hemender K, Reddy A, Pandurange Reddy V, Veeragaiah V (1992) Versatile synthesis of 6-alkyl/aryl-l/7-pyrazolo[3,4-d]pyrimidin-4[5//]-ones. Ind J Chem 316 163 166 Misono M, Okuhara T (1993) Solid superacid catalysts. Chem Tech 23(1I) 23 29 Kozhevnikov IV (1987) Advances in catalysis by heteropolyacids. Russ Chem Rev 56 811-825 Izumi Y, Urabe K, Onaka M (1992) Zeolite, elay and heteropoly acid in organic reaction, vol 99. Kodansha, Tokyo... 

Zhao, Z. Sun, W. Yang, X. Ye, X. Wu, Y. (2000). Study of the catalytic behaviors of concentrated heteropolyacid solution. I. A novel catalyst for isobutane alkylation with butenes. Catal. Lett., 65,115-121, ISSN1011-372X. 

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