Isomerization eugenol

As described above, however, some rather small differences could be observed, taking into account the superheating effect of the solvent under the action of micro-waves in the absence of any stirring. This probably occurs in the isomerization of sa-frole and eugenol in ethanol under reflux [31] (MW 1 h, A 5 h to obtain equivalent yields). 

Eugenol is a natural product available from a variety of essential oils (cinnamon-tree or pimentos leaves). Its isomerization (Eq. 49) into isoeugenol, the starting material for synthetic vanillin, is rather difficult and proceeds in modest yields under relatively harsh conditions. It can, however, be very efficiently prepared by use of 2.2 molar equivalents of base and catalytic (5 %) amounts of Aliquat in the absence of solvent. 

Eugenol undergoes MW-assisted isomerization to isoeugenol under solvent-free condition in the presence of potassium tert-butoxide, t-BuOK, and a catalytic amount of phase transfer reagent [34]. 

Synthesis from Eugenol. The sodium or potassium salt of eugenol is isomerized to isoeugenol by heating. Isomerization can also be carried out catalytically in the presence of ruthenium [164] or rhodium [165] compounds. 

Keywords eugenol KOH, phase transfer catalyst, microwave irradiation, isomerization, isoeugenol... 

Another occasionally useful transformation of allylphenols is the isomerization to propenylphenols by strong alkali, as in the well-known isomerization of eugenol to isoeugenol. For example, 2-methoxy-6-allylphenol (LXXI) is changed to the propenyl compound LXXII by... 

Since isoeugenol is the important intermediate in the vanillin production from eugenol, the isomerization of eugenol attracted a considerable amount of attention. The first report on the isomerization reaction appeared in 1891, in which Tiemann reported 50% conversion in 24 hours using an ethanolic KOH solution at 80°C [13]. 

Peterson et al (1933) applied this method to study the kinetic of eugenol isomerization by chromatographic and spectroscopic techniques [14]. Lampman et al (1977) used the same alkaline solution method run in dimethyl sulfoxide, and obtained 80% conversion after 2 hours reaction at temperatures higher than 170°C [7]. Andrieux et al (1977) obtained 92% isoeugenol with 2 hours of reaction time using RhCU as a catalyst run at 20 oC [15]. Isoeugenol could also be obtained by adding KOH and hexa-decyl-tributylphosphonium bromide to clove oil at 150°C [16]. 

Isomerization of safrole and eugenol is reported to occur when these alkenes are irradiated in the presence of iron carbonyls. Co-ordinatively unsaturated iron carbonyls are first formed and subsequently give iron carbonyl-alkene complexes whose alkene ligands are then isomerized. A further reported photoinduced isomerization involves Fe(fnb-Ti -cot)(CO)3 (cot = cyclo-octatetraene), which on irradiation in a CH4 matrix at 12 K is converted into Fe(cfiair-Ti -cot)(CO)3 via Fe(T -cot)(CO)3 as intermediate. The results of these studies are related to the fluxional behaviour of Fe(i7 -cot)(CO)3 in solution. ... 

Safrol, eugenol methyl ether, apiol and isoapiol yield a mixture of two isomeric acetates, one of which is crystalline, the other syrupy. 

Derivation From eugenol by isomerization with caustic potash. 

The Y, P and M zeolites with Si02/Al203 ratios of 3.9, 24 and 32, respectively, produced via recrystallization from the natural clinoptiolite in palladium form (0.62 - 6.16% Pd) at 413-458K in He, H2 and air atmosphere isomerize jC-eugenol basically into traw-woeugenol with 70-93% selectivity dihydroeugenol is also produced in the H2 atmosphere. The Pd-forms M and p are most active in the He atmosphere. Induction period at the beginning of the reaction observed in the helium atmosphere at temperature over 425 K is reduced in the air atmosphere and with 2-6% Pd content in the catalyst the condensation and oxidation reactions are rather intensive. 

P-26 - Isomerization ofp-eugenol on palladium-containing zeolites Ts.M. Ramishvili, M.K. Charkviani andL.D. Kashia... 

The phenolic primary alcohols derived in this way from phenylalanine (Phe, F) and in some systems from tyrosine (Tyr, Y) are incorporated into structural plant materials by linking carbohydrates (Chapter 11) together to form Ugnins. The same alcohols give rise to phenylpropenes, such as eugenol and safrole, which are commonly referred to as essential oils, while further oxidation and double-bond isomerization of p-coumaric acid leads to umbeUiferone (Figure 12.6). 

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