Vanillin Eugenol

For the manufacture of vanillin, eugenol is first isomerised to iso-eugenol, in which a rearrangement in the side chain has taken place. 

Vanillin Eugenol Serratia species, Klebsiella species, Enterobacter species Vanilla... 

Keywords antioxidant activity, citral oxidation, linalool, lemonene, octyl acetate, anise aldehyde, vanillin, eugenol, capillary gas chromatography. 

Tolutaimm balsamum Tolu balsam Myroxylon balsamum (L.) HARMS var. balsamum Fabaceae Leguminosae HELV VII, USP XXII, MD About 7.59I1 cinnamein , a mixture of benzoyl benzoate (4%-13%) and cinnaraoyl benzoate (1-3%) about 80% resin (mostly cinnamic esters of toiuresitannol), citmamic acid, benzoic acid, vanillin, eugenol... 

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. 

Other commonly occurring chemical groups ia essential oils iaclude aromatics such as P-phenethyl alcohol, eugenol, vanillin, ben2aldehyde, cinnamaldehyde, etc heterocycHcs such as iadole (qv), pyra2iaes, thia2oles, etc hydrocarbons (Liaear, branched, saturated, or unsaturated) oxygenated compounds such as alcohols, acids, aldehydes, ketones, ethers and macrocyclic compounds such as the macrocyclic musks, which can be both saturated and unsaturated. 

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. 

The typical flavour of sour cherries is produced during processing into wine, liqueur, juice, jam or fruit sauce. Benzaldehyde has been determined to be the most important aroma compound in sour cherries [82], but benzyl alcohol, eu-genol and vanillin are also important flavour compounds (Table 7.2, Fig. 7.5) [83]. Growing and storage conditions affect the concentration of benzaldehyde, benzyl alcohol, eugenol and vanillin [83, 84], and cold and rainy weather produces sour cherries with a less delicate sour cherry aroma [83]. 

In this chapter chemical conversions of natural precursors resulting in flavour chemicals are discussed. The main groups of natural precursors are terpenes for all kinds of terpene derivatives, vanillin precursors like lignin and eugenol, sugars for Maillard-associated flavour chemicals, amino acids and molecules obtained by fermentation or available as residual streams of renewable resources. 

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. 

The bioconversion of eugenol and ferulic acid to vanillin was first characterised in Pseudomonas fluorescens (Scheme 26.4) [36, 37]. However, an enzyme of the pathway, vanillin NAD+ oxidoreductase, catalysed the removal of vanillin from the medium through the formation of vanillic acid [38]. Deletion of the oxidoreductase was, however, only partially successful, largely because vanillin is also the substrate of coniferyl aldehyde dehydrogenase, an enzyme of the eugenol degradative pathway present in Pseudomonas sp. [39]. 

Scheme 26.4 Cloned genes and characterised enzymes involved in the conversion of eugenol and ferulic acid to vanillin in Pseudomonas sp. (adapted from [35])...

For example, vanillin can be obtained via at least five different ways (i) by isolation from the orchid (Vanilla planifolia), which is a very expensive method (ii) by tissue culture followed by extraction (iii) by microbial transformation of eugenol, the main compound of clove (iv) from lignine by synthesis, and (v) from guaiacol, a natural aroma compound, with comparable molecular structure. Only the vanillin obtained via the first three methods is natural. The other routes afford a nature-identical vanillin. 

Exercise 26-12 Devise a reasonable sequence of synthetic steps for conversion of eugenol to the flavoring material vanillin, which is 3-methoxy-4-hydroxybenzene-carbaldehyde (Section 26-5). 

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