Selective Formation of Epoxylimonene Catalyzed by Phosphonyl/Arsonyl Derivatives of Trivacant Polyoxotungstates at Low Temperature

Abstract

The catalytic performances of three organophosphonyl/arsonyl derivatives of POMs were evaluated for the epoxidation of limonene in acetonitrile, using aqueous H2O2 as the oxidant. All three W‐based POMs catalysts operated without any additional transition‐metal ions and displayed excellent conversion for limonene at temperatures varying from 4 to 50 °C. Furthermore, the use of B,α‐[NaHAsW9O33{P(O)R}2]3– (R = tBu, ‐CH2CH2CO2H) complexes led to the complete conversion of limonene to epoxylimonene at 4 °C. The selectivity of the reaction was modulated by varying the reaction solvent, and it was found that allylic reactions were favored in ethanol. The effect of the catalyst protonation was also investigated by DFT calculations, highlighting the role of protons in the epoxidation process.

DFT Studies of the Activity and Reactivity of Limonene in Comparison with Selected Monoterpenes

“…In 2003, in accordance with the European directive (2003/15/EC), limonene was classified as an allergen [11]. Pure limonene has no allergic properties; however, in the presence of molecular oxygen in the form of long-term contact with air, its autoxidation is possible, and the limonene hydroperoxides formed as a result of this reaction are responsible for allergic reactions [12].…”

“…Compared to products obtained using dioxygen as an oxidant, diepoxide (DLO), 8,9-LO, or polymer were additionally formed. For HOOH, the following complexes were used: cobalt sandwich-type polyoxometalates [39], tungstophosphates [2], polyoxotungstates [11], Schiff base complexes with Co(II) and Cu(II) and the same compounds but immobilized in zeolite-Y [40], manganese(II) acetylacetonate on MCM41 [41], Al 2 O 3 [42], the ions of non-transition metal [1], methyltrioxorhenium with different ligands [43], activated carbon where the active phase was the magnetite Fe 3 O 4 [44] or MoO 2 [45], complexes of VO and copper(II) with Schiff base ligands entrapped in the supercages of zeolite-Y [46], homogeneous and heterogeneous VO and iron(II) with Schiff base ligands [47], γ-Fe 2 O 3 /SiO 2 -NHFeP prepared from nanospheres and 5,10,15,20-tetrakis (pentafluorphenylporphyrin) iron(III) [48], heterogeneous Mn(III), Fe(III), and Co(III) porphyrin-based complexes immobilized on zeolite [49] or others complexes based on zeolite-Y [50][51][52] in which enclosing the catalyst in the porous structure of the support prevents the dimerization of the complexes, ensuring their catalytic activity. Catalysts used with t-butyl hydroperoxide as the oxidant are also zeolites, e.g., zeolite-Y with entrapped VO with Schiff base ligands [50], organic hybrid materials [26,53], Ti-MCM-41, and Ti-MWW compounds [54], iron(II) [55], molybdenum(II) complexes [56], salen-like Jacobsen's catalysts with manganese(III) [57] or carbon-based complexes with cobalt(II) acetylacetonate [58].…”

Halide-free CO2 cycloaddition onto styrene oxide catalysed by first row transition-metal derivatives of polyoxotungstates

“…4 In particular, their utilization allowed the reaction of CO 2 with epoxides under mild conditions, a prerequisite for a one-pot oxidative carboxylation. 5 Regarding epoxidation, efficient catalysts (OxCat) were reported for decades, including polyoxometalates (POMs) or their transition-metal substituted derivatives (M-POMs) 6 which are a widely studied class of molecular compounds allowing the activation of O 2 7 or H 2 O 2 8 under mild conditions. However, to date, publications dealing with the global oxidative cycloaddition cascade remain scarce.…”