Heterogeneous epoxidation with hydrogen peroxide

A shortcoming of these catalysts, in common with supported titanium catalysts, is their hydrophilicity which precludes effective catalysis with hydrogen peroxide. Hence, much effort has been devoted to the synthesis of hydrophobic analogs of these materials [54] but this has not yet resulted in the synthesis of truly effective catalysts for epoxidations with hydrogen peroxide. Apparently, hydrophobicity is not the only requirement for an effective heterogeneous Ti catalyst for epoxidations with hydrogen peroxide. 

Dilute (30%) hydrogen peroxide is less hazardous than organic hydroperoxides. Also, because water is an innocuous by-product, from an environmental point of view, the use of hydrogen peroxide rather than organic hydroperoxide is desirable. Indeed, the heterogeneous catalytic process for the manufacture of PO is based on the use of TS-1 and 30% hydrogen peroxide. The basic mechanism of epoxidation with hydrogen peroxide is very similar to that of reaction S.5.2.3. 

General G. Centi, F. Cavani, F. Trifiro, Selective Oxidation by Heterogeneous Catalysis, Kluwer Academic/Plenum Publishers, New York, 2001 G. Ertl, H. Knotzinger, J. Weitkamp, (Eds.), Handbook of Heterogeneous Catalysis, Volume 5, Wiley-VCH, Weinheim 1997 R.A. Sheldon, J.K. Kochi, Metal Catalyzed Oxidations of Organic Compounds, Academic Press, New York, 1981 G. Strukul (Ed.), Catalytic Oxidations with Hydrogen Peroxide as Oxidant, Kluwer, Dordrecht, 1992 K. Weissermel, H.-J. Arpe, Industrial Organic Chemistry, 4th Edition, Wiley-VCH, Weinheim 2003. Epoxidations J.C. Zomerdijk, M.W. Hall, Catal. Rev. Sci. Eng., 1981, 23, 163 ... 

Whereas so far oxidation reactions with O2 have been discussed, an important heterogeneous catalytic oxidation reaction is the epoxidation of propylene to propylene epoxide. Using hydroperoxide the reaction can be done over Ti dispersed on silica [133]. Ti becomes 4 coordinated as Si in Si02. With hydrogen-peroxide the reaction has been found to occur for Ti incorporated in the lattice of MFI zeolite [134]. The unique property of these systems is that the electrophilic nature of oxygen intermediates does not cause reaction with the allylic CH bond. It is proposed that the adsorbed intermediate is ... 

K. Yamaguchi, C. Yoshida, S. Uchida, N. Mizuno, Peroxotungstate immobilized on ionic liquid-modified silica as a heterogeneous epoxidation catalyst with hydrogen peroxide, J. Am. Chem. Soc. 127 (2005) 530. 

Epoxides are versatile intermediates in organic synthesis. The most general reagents for conversion of aUcenes to epoxides in homogeneous conditions are peroxycarboxyUc acids. The oxidation is believed to be a concerted process. Moreover, a process to avoid acidic conditions involves reaction with hydrogen peroxide. There is a clear demand for solid materials that catalyze epoxidations, therefore heterogeneous epoxidation remains a very active field of research [51]. 

While TS-1 is an ideal candidate for epoxidation of small linear alkenes with hydrogen peroxide, it has been reported to be less successful for large bulkier alkenes. This has been attributed to size/diffusion limitations associated with its microporous structure. Despite this limitation, the development of TS-1 assisted in the creation of a new type of solid, recyclable catalyst called a redox molecular sieve and subsequently enabled selective organic oxidation reactions to encompass many principles of green chemistry via heterogeneous catalysis. 

Yamaguchi, K., Yoshida, C., Uchida, S., et al. (2005). Peroxotungstate Immobilized on Ionic Liquid-Modified Silica as a Heterogeneous Epoxidation Catalyst with Hydrogen Peroxide,... 

A particularly interesting system for the epoxidation of propylene to propylene oxide, working under pseudo-heterogeneous conditions, was reported by Zuwei and coworkers [61]. The catalyst, which was based on the Venturello anion combined with long-chained alkylpyridinium cations, showed unique solubility properties. I11 the presence of hydrogen peroxide the catalyst was fully soluble in the solvent, a 4 3 mixture of toluene and tributyl phosphate, but when no more oxidant was left, the tungsten catalyst precipitated and could simply be removed from the... 

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