Novel access to verbenone via ruthenium nanoparticles-catalyzed oxidation of α-pinene in neat water

Abstract

Graphical abstractResearch Highlights  Ruthenium nanoparticles proved to be active in pinene oxidation in neat water. An average yield towards verbenone of 41% was achieved. Radical species are involved in the allylic oxidation.This catalytic process used eco-respectful reagent (t-BHP) and solvent (H2O). AbstractAqueous suspensions of Ru(0) nanoparticles, stabilized with hydroxyethylammonium salts and possessing sizes around 2 nm, proved to be active and selective in the mild oxidation of -pinene in the presence of tert-butylhydroperoxide, in neat water. Verbenone, a product of great interest for fine chemistry, was obtained as major product with yield up to 41% under optimized conditions. 2-hydroxy-3-pinanone was identified as a co-product of the reaction, but with very low amount (< 7%). Kinetic investigations allowed determining the potential reaction intermediates and by-products. Moreover, mechanistic studies with radical scavengers confirmed that -pinene oxidation mainly implies both carbon-and oxygen-centered radicals.

Fabrication of Bimetal CuFe2O4 Oxide Redox-Active Nanocatalyst for Oxidation of Pinene to Renewable Aroma Oxygenates

“…The direct catalytic upgrading of turpentine still remains a challenge because of the high variety of its constituent’s reactivity, therefore various pre-treatment steps are required to separate individual components [6,7,8,9,10]. On the other hand, the oxidation and epoxidation of terpenes C–C (alkane) and C=C (olefin) bonds has become an efficient chemical transformation for upgrading their inert hydrocarbon C–H bond into valuable oxygenated chemical derivatives [11,12,13]. As a result, the liquid-phase oxidation of pinene provide an attractive route to the synthesis of the high-value aroma oxygenates such as verbenone, verbenol and pinene oxide (Scheme 1) [5].…”

Catalytic Oxidation Processes for the Upgrading of Terpenes: State-of-the-Art and Future Trends

“…Catalysts 2019, 9, 893 32 of 38 Figure 16. Ammonium surfactant-stabilized ruthenium nanoparticles for oxidation of α-pinene 1 in neat water (adapted from reference [90]).…”

“…Moreover, most of the oxidation processes still suffer from various drawbacks, such as the use of too sophisticated catalysts, toxic organic solvents, and high amounts Although many works have been carried out for the allylic oxidation of olefinic terpenes, most processes still suffer from some drawbacks such as moderate conversions and/or selectivities, sophisticated catalytic systems, toxic organic solvent as well as huge amounts of oxidant, long reaction times and difficult catalyst's recycling. It is noteworthy to underline that two examples for the allylic oxidation of α-pinene 1 were carried out in water as a green reaction media, with polymer-supported nickel catalyst [41] or with aqueous suspensions of ruthenium nanoparticles [90].…”

“…Although Co 3 O 4 nanoparticles in organic media (DMF) were reported for the epoxidation of α-pinene 1 [87], the use of metallic nanoparticles finely dispersed in water, as a cheap, available and benign solvent [88,89], has not been described yet. In that context, our team have very recently developed aqueous suspensions of ruthenium (0) nanoparticles, stabilized with a hydroxyethylammonium salt (HEA16Cl) and possessing sizes around 2.0 nm, for the mild allylic oxidation of α-pinene, with tert-butylhydroperoxide in neat water ( Figure 16) [90]. After optimization of the reaction conditions, verbenone 8 was obtained as major product with a yield up to 41%, alongside 2-hydroxy-3-pinanone 54 (<7%) as co-product.…”

Selective Allylic Oxidation of Terpenic Olefins Using Co-Ag Supported on SiO2 as a Novel, Efficient, and Recyclable Catalyst

“…e allylic oxidation of mono and sesquiterpenic natural olefins, cheap constituents of essential oil extracted from plants [9], constitutes a great route for the synthesis of a wide range of oxygenated products with high added values such as aldehydes, alcohols, ketones, esters, ethers, and phenols [10].…”