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The Strained Sesquiterpene β‐Caryophyllene as a Probe for the Solvent‐Assisted Epoxidation Mechanism
Author(s) -
Steenackers Bart,
Neirinckx Alexander,
De Cooman Luc,
Hermans Ive,
De Vos Dirk
Publication year - 2014
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201300981
Subject(s) - chemistry , reactivity (psychology) , solvent , moiety , hydrogen bond , catalysis , organic chemistry , photochemistry , molecule , medicine , alternative medicine , pathology
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 H 2 O 2 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 OO bond of H 2 O 2 in the transition state through hydrogen‐bond donation to the leaving OH moiety of H 2 O 2 . α‐Humulene was found to possess similar reactivity as β‐caryophyllene whereas isocaryophyllene—the unstrained isomer of β‐caryophyllene—was unreactive.