Chemphyschem

Publication date: 2014-01
Volume: 15 Pages: 966 - 973
ISSN: 1439-4235, 1439-7641 PMID: 24615908
DOI: 10.1002/cphc.201300981
Publisher: Wiley

Author:

Steenackers, Bart
Neirinckx, Alexander ; De Cooman, Luc ; Hermans, Ive ; De Vos, Dirk

Keywords:

density functional calculations, epoxidation, hydrogen bonds, kinetics, solvent effects, Science & Technology, Physical Sciences, Chemistry, Physical, Physics, Atomic, Molecular & Chemical, Chemistry, Physics, SOLVATOCHROMIC COMPARISON METHOD, SOLVATION ENERGY RELATIONSHIPS, PI-STAR SCALE, HYDROGEN-PEROXIDE, FLUORINATED ALCOHOLS, OLEFIN EPOXIDATION, CATALYTIC ROLE, ACTIVATION, ALPHA, REACTIVITY, 0306 Physical Chemistry (incl. Structural), 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics, 0307 Theoretical and Computational Chemistry, Chemical Physics

Abstract:

In our attempt to synthesize β-caryophyllene oxide in food-compatible conditions, we observed the uncatalyzed and highly selective epoxidation of β-caryophyllene, a strained bicyclic sesquiterpene, in ethanol with aqueous H2 O2 under radical-suppressing conditions without the addition of a catalyst. The unusual reactivity of β-caryophyllene allowed us to use it as a probe for the mechanism of the solvent-assisted epoxidation in a wide range of organic solvents. A kinetic study was performed to investigate the epoxidation mechanism; an excellent correlation was found between the observed epoxidation rates in different solvents and the Abraham's hydrogen bond formation parameters of these solvents. By means of computational analysis, it was found that the main role of the solvent consists of the stabilization of the elongated OO bond of H2 O2 in the transition state through hydrogen-bond donation to the leaving OH moiety of H2 O2 . α-Humulene was found to possess similar reactivity as β-caryophyllene whereas isocaryophyllene-the unstrained isomer of β-caryophyllene-was unreactive.