Vanillin isoeugenol

A number of other valuable aroma chemicals can be isolated from essential oils, eg, eugenol from clove leaf oil, which can also, on treatment with strong caustic, be isomerked to isoeugenol, which on further chemical treatment can be converted to vanillin (qv). Sometimes the naturally occurring component does not requke prior isolation or concentration, as in the case of cinnamaldehyde in cassia oil which, on dkect treatment of the oil by a retro-aldol reaction, yields natural ben2aldehyde (qv). This product is purified by physical means. 

The manufacture of vanillin shows the progress made in the chemistry and chemical engineering of the substance. Most commercial vanillin is synthesized from guaiacol the remainder is obtained by processing waste sulfite Hquors. Preparation by oxidation of isoeugenol is of historical interest only. 

By direct oxidation by means of ozone, isoeugenol is converted into vanillin. 

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is widely used in foods, beverages, perfumes and the pharmaceuticals industries. Biotransformation of isoeugenol from essential oil to vanillin represents an economic route for the supply of vanillin, which has a limited supply due to the availability of vanilli pod plants. The conversion yield of isoeugenol to vanillin by the whole-cell biotransformation process of Bacillus fusiformis was low due to the product inhibition effect. Adding resin HD-8 to the whole-cell biotransformation eliminated the product inhibition effect, yielding 8 gL 1 of vanillin in the final reaction mixture [27]. The resin HD-8 also facilitated the separation of vanillin from the used substrate. The recovered isoeugenol can be used for the subsequent biotransformation reaction. 

Zhao, L.-Q., Sun, Z.-H., Zheng, P. and He, J.-Y. (2006) Biotransformation of isoeugenol to vanillin by Bacillus fusiformis CGMCC1347 with the addition of resin HD-8. Process Biochemistry (Barking, London, England), 41, 1673-1676. 

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. 

Isoeugenol can be hydrogenated catalytically to form dihydroeugenol. Vanillin was formerly prepared by oxidation of isoeugenol. Additional fragrance materials are prepared by esterification or etherification of the hydroxyl group. 

Li YH, Sim ZH, Zao LQ, Xu Y (2005) Bioconversion of isoeugenol into vanillin by crude enzyme extracted from soybean. Appl Biochem Biotechnol 125 1-10... 

Zhao LQ, Sun ZFl, Zheng P, Zhu LL (2005) Biotransformation of isoeugenol to vanillin by novel strain of Bacillus fusiformis. Biotechnol Lett 27 1505-1509... 

Eugenol obtained from clove oil is an important precursor for the preparation of vanillin (Scheme 13.10). The reaction consists of two steps. First, eugenol needs to be converted into isoeugenol, which requires alkaline treatment or ruthenium or rhodium catalysis. Second, the isoeugenol is oxidised to vanillin using, for instance, chromic acid. This method results in nature-identical vanillin. 

Eugenol has been used as a feedstock in the production of isoeugenol, which is needed in the manufacture of vanillin. Methylation of eugenol yields methyleugenol, which acts as a sex attractant for a certain type of fly (Dacus dorsalis) [7,8]. 

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]. 

Scheme 5 MTO-catalyzed oxidative cleavage of isoeugenol and trans-iemlic acid to vanillin [89]...

The classical synthesis of vanillin from eugenol or isoeugenol was developed in 1896 and it remained the preferred method for about 50 years. Vanillin is now prepared industrially in large amounts by the Reimer-Tiemann reaction, starting with... 

Eugenol.—The firm v. Hey den Echfg.4 obtains vanillin elec-trolytically from eugenol. The latter is rearranged by alkalies into isoeugenol and then oxidized electrolytically in alkaline solution ... 

The earliest example of ozonation of a model compound with an alkene side chain is that of isoeugenol (Wood 1923). The anticipated product, vanillin, may be obtained in yields as high as 90% because of the retardation of further oxidation by the deactivating aldehyde group. Systematic studies on models of this type have been reported by Eriksson and Gierer (1985). The investigation by Kolsaker and Bailey (1967) is also relevant. 

Very similar phenomena have been studied and observed with other olefins, such as anethol and isoeugenol (10, 11, 24)- In these cases the CO bands which appear almost at the beginning of the ozonization likewise develop in a definite way, denoting the definite formation of anisaldehyde and vanillin, respectively. 

As has been shown by Quest International [31], lipoxygenases also accept a relatively broad spectrum of phenolic compounds as substrates. Of interest to the flavour industry are the lipoxygenase-catalyzed conversions of isoeugenol and coniferyl benzoate from Siam resin to vanillin (4-15% peld. Fig. 7.12). At present, the commercialization of these biotransformations is hampered by the... 

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