Abstract
Catalyzed organic solvent-free (ep)oxidation were achieved using H3PM12O40 (M = Mo or W) complexes ionically grafted on APTES-functionalized nano-silica beads obtained from straightforward method (APTES = aminopropyltriethoxysilane). Those catalysts have been extensively analyzed through morphological studies (Dynamic Light Scattering (DLS), TEM) and several spectroscopic qualitative (IR, multinuclear solid-state NMR) and quantitative (1H and 31P solution NMR) methods. Interesting catalytic results were obtained for the epoxidation of cyclooctene, cyclohexene, limonene and oxidation of cyclohexanol with a lower [POM]/olefin ratio. The catalysts were found to be recyclable and reused during three runs with similar catalytic performances.
Highlights
Oxidation of olefins and alcohols are important reactions in organic chemistry, with fundamental and applicative interest of those chemical transformations [1,2,3,4,5,6,7,8,9,10]
Tetraethyl orthosilicate (TEOS, 98% Aldrich), ammonium hydroxide solution (25%, Aldrich), 3-aminopropyltriethoxysilane (APTES, 99%, Aldrich), cis-cyclooctene (CO, 95%, Alfa Aesar, Ward Hill, MA, USA), cyclooctene oxide (COE, 99%, Aldrich), cyclohexene (CH, 99%, Acros, Geel, Belgium), cyclohexene oxide (CHO, 98%, Aldrich), 2-cyclohexen-1-ol (CHol, 95%, TCI, Tokyo, Japan), 2-cyclohexen-1-one (CHone, 96%, TCI), cis-1,2-cyclohexanediol (CHD, 99%, Acros), limonene (Lim, 98%, Aldrich), limonene oxide (LO cis/trans mixture, 97%, Aldrich), (1S, 2S, 4R)-(+)-limonene-1,2-diol, L-carveol (Col cis/trans mixture, 95%, Aldrich), (R)-(-) Carvone (Cone 98%, Aldrich), cyclohexanol (CYol, 99%, Alfa Aesar, Karlsruhe, Germany), cyclohexanone (CYone, 99.8%, Acros), phosphotungstic acid hydrate, molybdatophosphoric acid hydrate and TBHP (70% in water, Aldrich) were used as received
Powder X-ray diffraction: The solids were analyzed by X-ray diffraction (XRD) with a Bruker (Karlsruhe, Germany) D2 X’Pert PRO diffractometer using Cu Kα radiation (40 kV and 40 mA)
Summary
Oxidation of olefins and alcohols are important reactions in organic chemistry, with fundamental and applicative interest of those chemical transformations [1,2,3,4,5,6,7,8,9,10]. Epoxides can be obtained using very efficient organic oxidants (m-CPBA [11], NaClO [12] and RCO3 H [13,14]) but with procedures needing long workup, detrimental for ecological and economical purposes Those issues can be diminished using metal-based catalysts, but some drawbacks of those processes come from the use of (toxic) metals and/or the use of (toxic) organic solvent(s). An elegant way to circumvent those issues, in straight line with the principles of green chemistry [17,18,19], is to diminish/suppress the use of organic solvent within the oxidation process We demonstrated it in several organic solvent-free processes we published with active (pre)catalysts (Mo, V or W based, complexes with tridentate ligands and/or polyoxometalates (POMs)), giving a first step towards a cleaner process [20,21,22,23,24,25,26,27,28,29,30,31]. Some of those cited processes could not allow an easy separation
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