A catalytic, environmentally benign method for the epoxidation of unsaturated terpenes with hydrogen peroxide

Sodium tungstate-catalyzed “On-water” synthesis of β-arylvinyl bromides

“…Water is a promising choice (28Á34) as the medium of organic reactions from the standpoint of sustainability and chemical safety. From the environmental perspective, hydrogen peroxide is a good choice as oxidant which was used for eco-friendly oxidation of olefins, alcohols, and sulfides (35), a-bromination of active methylene compounds with KBr in HCl (36), hydroxylation of haloarenes and heterohaloarenes (37), free radical bromination in aqueous HBr (38), and oxidation of alkenesÁarenes to ketones in aqueous HBr (39) (41), electrophilic bromination across olefin, acetylene, and ring bromination of aromatic rings using KBr, HBr, and NH 4 VO 3 (42). Inspired by the above literature precedence, we have ventured to explore the catalytic activity of relatively less-toxic Na 2 WO 4 for the ecocompatible synthesis of (E)-vinyl bromides in aqueous medium using KBr as a non-toxic brominating agent and H 2 O 2 as an eco-friendly oxidant.…”

Grafting of Molecularly Ordered Mesoporous Phenylene‐Silica with Molybdenum Carbonyl Complexes: Efficient Heterogeneous Catalysts for the Epoxidation of Olefins

“…[39,40] Conventional manufacturing processes based on stoichiometric peracid (RCO 3 H) routes are becoming increasingly unacceptable in the context of green chemistry (since equivalent amounts of acid waste are produced), and can suffer from the non-selective formation of mono-and diepoxides as well as cleaved products. [41][42][43] This has motivated the search for alternative methods based on catalytic epoxidation using either homogeneous or (preferably) heterogeneous catalysts. [39,41,[43][44][45] The oxidation of (R)-(+)-limonene with anhydrous TBHP using materials 2a or 2b as the heterogeneous pre-catalysts gave limonene oxide in 95% yield at 3 h reaction and no byproducts were detected, which reveals an outstanding regioselectivity to the epoxidation of the endocyclic double bond (Table 1).…”

“…[41][42][43] This has motivated the search for alternative methods based on catalytic epoxidation using either homogeneous or (preferably) heterogeneous catalysts. [39,41,[43][44][45] The oxidation of (R)-(+)-limonene with anhydrous TBHP using materials 2a or 2b as the heterogeneous pre-catalysts gave limonene oxide in 95% yield at 3 h reaction and no byproducts were detected, which reveals an outstanding regioselectivity to the epoxidation of the endocyclic double bond (Table 1). Comparable results were ob- tained for complex 1.…”

Kinetic Modeling of Limonene Epoxidation over PW-Amberlite

“…1 Several alternative heterogeneous catalytic systems have been reported to diminish the negative effects of processes that use environmentally unacceptable stoichiometric amounts of peracids. [2][3][4][5] For example, limonene conversions and selectivities higher than 80% and 90%, respectively, can be achieved under mild reaction conditions (24 h, 38°C) with hydrogen peroxide as the oxidant (eq 1 6,7 ) over PW-Amberlite, a catalyst obtained by the immobilization of a phosphotungstate complex on a commercial macroreticular ion-exchange resin. Because of the low solubility of aqueous hydrogen peroxide in limonene, a solvent is required to obtain high epoxide yields.…”