Self-assembled Na12[WZn3(ZnW9O 34)2] as an industrially attractive multi-purpose catalyst for oxidations with aqueous hydrogen peroxide

Peter T. Witte, Paul L. Alsters, Walther Jary, Ruth Müllner, Peter Pöchlauer, Dorit Sloboda-Rozner, Ronny Neumann

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

Eleven W-based catalyst systems for alkene epoxidation with aqueous H 2O2 were compared under identical conditions and at equal level of 0.1 mol % W-atoms. Of these, those based on a combination of H 2WO4 and a methyltrioctylammonium phase transfer catalyst turned out to be most active in particular systems that contain a source of phosphate. Evidence is presented that under our conditions the actual epoxidizing species in H2WO4-based catalyst systems without phosphate source is mononuclear [WO(OH)(O2)2] - rather than binuclear [{WO(O2)2} 2O]2- that is usually thought to be active. For large-scale applications, however, the polyoxometalate Na12[WZn 3-(ZnW9O34)2] (NaZnPOM) in combination with a suitable phase transfer catalyst such as methyltrioctylammonium chloride is preferred over H2WO 4-based catalysts. This preference results from the fact that use of H2WO4 requires a catalyst activation step that is troublesome on a large scale, whereas epoxidations catalyzed by NaZnPOM start without induction period on addition of H2O2. Optimizations of epoxidations catalyzed by QCl/NaZnPOM or QCl/H 2WO4 have shown that the optimum Q/W ratio depends on the alkene that is epoxidized and differs from that expected from catalyst stoichiometry. An attractive feature of NaZnPOM from the viewpoint of industrial applicability is that epoxidations and other reactions with H2O 2 are efficiently catalyzed by a readily available aqueous solution of NaZnPOM prepared through self-assembly. A 1 mol scale example is provided of an epoxidation catalyzed by a combination of self-assembled NaZnPOM and Luviquat mono CP as a multifunctional cocatalyst with emulsifying, buffering, and phase-transferring properties.

Original languageEnglish
Pages (from-to)524-531
Number of pages8
JournalOrganic Process Research and Development
Volume8
Issue number3
DOIs
Publication statusPublished - May 1 2004

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry

Fingerprint Dive into the research topics of 'Self-assembled Na<sub>12</sub>[WZn<sub>3</sub>(ZnW<sub>9</sub>O <sub>34</sub>)<sub>2</sub>] as an industrially attractive multi-purpose catalyst for oxidations with aqueous hydrogen peroxide'. Together they form a unique fingerprint.

  • Cite this