Isoeugenol, oxidation

Isoeugenol is converted to vanillin through an epoxide-diol pathway leading to vanillyl alcohol as a precursor. The intermediates isoeugenol oxide and isoeugenol diol were identified in the biotransformation of isoeugenol with Bacillus pumilus S-1, which afforded 3.75 gl yield of vanillin in preparative biotransformation [39]. 

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. 

Isodurene, t98 Isoeugenol, ml08 Isohexane, m357 Isoleucinol, a211 Isomesityl oxide, m370... 

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. 

Already in 1897 Klason [52] suggested that gymnosperm lignin is derived from coniferyl alcohol. On the basis of experiments using isoeugenol as a model substance, Erdtman [53] advanced the hypothesis that lignin is a product of the oxidative polymerization of coniferyl alcohol ... 

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

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 ... 

Nakatsubo F, Higuchi T (1975) Synthesis of 1,2-diarylpropane 1,3 diols and determination of their configurations Holzforschung 29 193-198 Ralph J, Ede RM, Robinson NP, Main L (1987) Reactions of /f-aryl lignin model quinone methides with anthrahydroquinone and antranol J Wood Chem Technol 7 133 160 Ralph J, Young RA (1983) Stereochemical aspects of lignin model (S aryl ether quinone methide reactions J Wood Chem Technol 3 161-182 Sarkanen KV, Wallis AFA (1973) Oxidative dimerizations of (E)- and (Z) isoeugenol (2 methoxy-4-propenylphenol) and (E) and (Z)-2,6-dimethoxy-4-propenylphenol JCS Perkin I 1973 1869-1878... 

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. 

A biomimetic method was developed by Arnoldi and coworkers to synthesize propacin (31). Oxidation of an equimolar mixture of 35 and isoeugenol in toluene/ methanol with Ag20 at room temperature provided 30% of 31. A similar reaction has also been attempted with coniferyl alcohol (45) to synthesize 9 and 10 (72). 

Oxidation of olefinic side chains with ozone to form aromatic aldehydes gives erratic results and therefore other oxidants are employed. For this purpose, the most widely used oxidant is nitrobenzene in dilute alkali the mixture is allowed to react at moderate temperatures for several hours. Thus, hydroxy benzaldehydes may be obtained from propenyl-phenols, which in turn are readily prepared by the Claisen rearrangement of Oalkyl ethers (method 100). Sodium dichromate in the presence of sulfanilic acid, which removes the aldehyde as it is formed, gives yields as high as 86% in the oxidation of isoeugenol and isosafrole. ... 

Nitro compounds in alkaline medium are used for rather specific oxidations. 2-Nitropropane in the form of its sodium salt converts benzylic halides into aromatic aldehydes under fairly mild conditions [987. Nitrobenzene transforms isoeugenol [95S] and similar aromatic compounds with side chains that contain double bonds conjugated with the aromatic rings into aldehydes [988, 989], In the Skraup synthesis, nitrobenzene dehydrogenates the dihydroquinoline intermediate to quinoline. 

Mixtures of para- and ortho-substitutQd products are sometimes obtained, as in the anodic oxidation of electron-deficient tetrahydronaphthol (XLII), which gave a 5 2 mixture of para- and ortho-( umo acetates (XLIII and XLIV), as in Eq. (17) [46]. Similar results were reported for the anodic methoxylation of eugenol and isoeugenol [47]. 

Two useful groups of related reactions may be discerned here, both of which are observed for prope-nyl-phenols. The first type is illustrated by the oxidation of isoeugenol (255) with aqueous iron(IIl) chloride,which yields the threo- and erythro-stereomers (55%) of the hydroxy ether (256), presum-... 

The formation of Cp—Car bonds is illustrated by the generation of dehydrodiisoeugenol (286) from ( )-isoeugenol (257), enzymically with a mushroom juice (45%) yield, with horseradish peroxidase (65%), ° with iron(III) chloride (53%), by photooxidation (20%) and by (-)-a-phenylethylamine-copper(ll) nitrate (21%). In the last case a low enantiomeric excess was recorded. Coniferyl alcohol can be oxidized to dehydrodiconiferyl alcohol (287) with various enzyme oxidases. The cis... 

T Oki, K Oknbo, and H Ishikawa. The peracetic acid oxidation of isoeugenol and dehy-drodiisoeugenol. Mokuzai Gakkaishi 20 89-97, 1974. 

Aldehydes can also sometimes be obtained from olefins by oxidation with chromic acid or nitric acid, e.g., acetylvanillin from isoeugenol.111... 

Isoeugenol to Vanillin. The formation of vanillin from eugenol is an example of an oxidation of a side chain to an aldehydic group in which it is convenient to protect one substituent against oxidation. Eugenol obtained from oil of cloves is heated with an alkali such as sodium hydroxide to convert it to isoeugenol, the hydroxyl group is protected by acetylation, and the substance is oxidized and then saponified to vanillin. 

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