Recyclable solid catalysts for epoxidation of alkenes: Amino- and oniumsilica-immobilized [HPO 4{W 2O 2( μ-O 2) 2(O 2) 2}] 2− anion

• Published in: Journal of catalysis Vol. 249; no. 1; pp. 1 - 14
• Main Authors: Kovalchuk, T., Sfihi, H., Zaitsev, V., Fraissard, J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-07-2007; Elsevier
• Subjects: 31P NMR; Anion exchanger; Catalysis; Chemistry; Cyclooctene; Epoxidation; Exact sciences and technology; General and physical chemistry; H 2O 2; HPA; Immobilized; Ion-exchange; Limonene; Peroxocomplex; Silica; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; H 2O 2; Peroxocomplex; Cyclooctene; 31P NMR; HPA; Anion exchanger; Epoxidation; Limonene; Immobilized; Silica; 1,8-p-Menthadiene; Hydrogen peroxide; Hydrocarbon; 31 PNMR; H2O2; Solid; Heterogeneous catalysis; Alkene; Ethylenic compound; Catalyst
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2007.03.018

We designed solid catalysts for liquid-phase epoxidation based on functionalized silica
Si(CH
2)
3Q
+ [Q:
NH
3,
NEt
3,
NC
5H
5,
PPh
3] and [HPO
4{W
2O
2(
μ-O
2)
2(O
2)
2}]
2−. The approach that we adopted allowed us to avoid the use of chlorocarbon solvent and enabled catalyst recycling. By using supports with 4 different linking chains between the anion and silica and different surface lipophilicities, we followed their influence on catalyst activity in the epoxidation of cyclooctene and (R)-limonene by H
2O
2 in
t-BuOH. All solids were active in cyclooctene epoxidation (conversion up to 100%; epoxide selectivity 100%; TOF 2–4 h
−1 anion
−1). The degree of surface coverage by organic functions was crucial for recycling performance. Catalysts with low densities of organic functions and hydrophilic surfaces were easily deactivated. End-capping improved their stability but decreased their activity. Catalysts with dense coverage of onium groups and the active site in a hydrophobic chloropropyl environment demonstrated high activity and excellent recycling stability. Less promising results were obtained in the epoxidation of (R)-limonene.