Linalool to geraniol/nerol isomerization catalyzed by (RO)3VO complexes: studies of kinetics and mechanism

Abstract

Abstract Highly selective catalytic system {(RO)3VO+[(Bu)4N+]OH} for the process of linalool to geraniol + nerol isomerization within the temperature range of 413–513 K is reported. Using the 51 V NMR spectroscopy, composition and reactivity of vanadium complexes formed in the catalytic system were investigated. Mononuclear vanadium complexes (RO)3−n(R′O)nVO, where RO-linalyl and R′O-geranyl/neryl ligands, n=0, 1 and 2, are active in the isomerization reaction. The reaction of the ligand {linalool/(geraniol+nerol)} exchange is very fast and reversible, the equilibrium constant of this reaction was estimated. The rate determining step of the isomerization process is the rearrangement of the coordinated to vanadium linalyl- to geranyl/neryl ligands which, probably, proceeds via reduction–oxidation mechanism. The isomerization of linalool is a reversible reaction and two isomers (geraniol and nerol) are formed by the parallel routs. The equilibrium constant of the linalool/(geraniol+nerol) as well as geraniol/nerol isomerization slightly depends on temperature. The reaction rate is of the first-order on linalool, geraniol and nerol concentrations. The kinetic scheme and mechanism of linalool to geraniol+nerol isomerization are suggested.