Palladium-Catalysed Oxidation of Bicycle Monoterpenes by Hydrogen Peroxide in Acetonitrile Solutions: A Metal Reoxidant-Free and Environmentally Benign Oxidative Process

Abstract

Currently, the oxidative transformations of natural olefins are complicated for competitive reactions such as isomerization, skeletal rearrangements and nucleophilic addition. These concurrent reactions are promoted by metal reoxidant, normally a Lewis acid, and by protic solvent. In this article, the oxidation of terpenes, namely camphene, b-pinene, a-pinene and 3-carene were performed in PdCl 2 /H 2 O 2 /CH 3 CN system. This metal reoxidant-free system showed highly efficient, especially on camphene and b-pinene oxidation, which resulted in the selective conversion of these substrates into epoxy-derivates and allylic oxidation products, respectively. Additionally, the effects of the principal reactional parameters such as the peroxide/catalyst and substrate/catalyst molar ratio were also investigated.

New Sustainable Synthetic Routes to Cyclic Oxyterpenes Using the Ecocatalyst Toolbox

“…Although the yield of this reaction remained moderate, it was better than gold, palladium, molybdenum, niobium, titanium and tungsten systems, and equivalent to the yield using other manganese catalysts [ 47 , 54 , 55 , 56 , 57 ]. However, the conditions described here are eco-friendlier.…”

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

“…Oxidation of olefins by dioxygen, using Wacker-type systems (PdCl 2 /CuCl 2 ), is quite limited, owing to the formation of many co-products due to the Lewis acidity of CuCl 2 [15]. Alternatively, da Silva et al designed a CuCl 2 -free oxidative process based on a PdCl 2 /H 2 O 2 /CH 3 CN combination [16] that could improve the selectivity toward oxidation products (Table 1). First, a blank test on camphene 18 without catalyst afforded only 10% of epoxide 19 in 6 h, in standard conditions (Table 1, Entry 1).…”

“…Oxidation of camphene 18 catalyzed by palladium salts a (adapted from reference[16]). Reaction conditions: Camphene (2.5 mmol), H 2 O 2 , 60 • C, CH 3 CN (10 mL), 12 h. b Determined by GC analyses.…”

Pd(OAc)2/M(NO3)n (M=Cu(II), Fe(III); n=2, 3): Kinetic investigations of an alternative Wacker system for the oxidation of natural olefins

“…Recently, we have reported an oxidative system based on palladium where high selectivities and yields were also reached on terpenes oxidation [43]. However, the final oxidant employed was hydrogen peroxide in acetonitrile solutions.…”