Vanillin synthesis

FIGURE 9.29. Catalytic vanillin synthesis Rhodia process. 

Aroma. Chemicals. Specialty chemicals produced either by extraction from natural sources or by synthesis, such as vanillin [121 -33-5],... 

Guyot and Gey have prepared vanUlin by a synthesis depending on the property possessed by compounds containing t-wo carbonyl groups in juxtaposition, of condensing with guaiacol giving products from which it is easy to pass to vanillin. 

The opiate alkaloid, papaverine, from Papaver somniferum is an anti-spasmodic, vasodilator, and smooth muscle relaxant. Its total synthesis has been studied since Pictet and Gams early work in 1909 and has since been followed up by various industrial syntheses up till the early 1950s using important industrial commodities as vanillin, acetovanillone, veratraldehyde (methylvanillin), and homoveratric acid as starting materials (see Figure 4.50). Table 4.23 summarizes the results of the five synthetic plans for this natural product. All are convergent... 

Several syntheses exist for vanillin. A process recently developed by Rhodia seems to be superior [11]. The process (Scheme 5.2) involves four catalytic steps starting from phenol aromatic ring hydroxylation, O-methylation, hydroxymethyl-ation, and oxidation. The process combines elegance and precision in organic synthesis. 

Another example of the substitution of classic routes for chemical synthesis by multistep catalytic processes is the Rhodia vanillin process (Figure 9.10), which involves four steps, all employing a heterogeneous catalyst. 

The chemical and enzymatic oxidative degradation of lignin (and coal) is used to obtain not only vanillin and benzoic acid, but also other aromatics (Baciocchi et al. 1999, references therein). In principle, lignin could be a major nonfossil and renewable source of aromatic compounds, a feedstock for synthesis of useful products. The problem deserves finding new ion-radical routes to cleave lignin. At present, there is some shortage in oil, gas, and even coal, which had usually been well-available natural sources of aromatics. In the near future, biomass may (and must) replace fossil-originated materials in the manufacture of commercial carbon-based products. 

Validation of the role of femloyl-CoA in the synthesis of the vanillin precursor will be detection of the appropriate intermediates and/or enzyme activities in placental extracts that could account for the production of the predicted levels of capsaicinoids. The presence of low levels of monolignol intermediates could be explained by lignin biosynthesis. An alternate route from phenylalanine to vanillin has been considered by some investigators Orlova et al. [68] demonstrated the role of the benzenoid pathway in petunia flowers for the biosynthesis of phenylpropanoid/benzenoid volatiles. 

Tyramine is derived by using 4-hydroxybenzaldehyde as the starting material. Vanillin and 0-vanillin can also be used in this synthesis to make the tyramine analogs 2-hydroxy-3-methoxy-B-phenylethylamine and 3-methoxy-4-hydroxy-B-phenylethylamine, respectively. Vanillin is less suspicious to purchase and the potency and elfects of the vanillin made drug are about the same as Tyramine. 

Hydroxy-3-methoxy-B-nitrostyrene. A mixture of methylamine hydrochloride (7 g, see precursor section for synthesis) and 10 g of sodium carbonate in 100 ml of methanol is stirred well, filtered, and added to a solution of 219 g of vanillin and 85 ml of nitromethane in 600 ml of ethanol. Keep this solution in the dark at room temp for 71 hours to make the nitrostyrene crystallize out. Filter and wash with cold methanol. Yield 225 grams, nip 166-168°. This and the other two nitriles are reduced by the method listed in the reduction section, JACS, 72, 2781. This reduction can be used to reduce many of the nitro type compounds. 

Methods of synthesis of levodopa from vanillin [8-14] have been suggested. According to one of them, condensation of vanillin with hydantoin and the subsequent reduction of the double bond in the formed product (10.1.4), after hydrolysis, gives racemic DOPA from which levodopa is isolated [8]. 

Figure 4.3. Using the example of one synthetic route to vanillin (see Figure 4.1), one problem of the lack of specificity of chemical reagents is revealed—two products, not one, are produced, if a long sequence of chemical reactions is needed to convert a cheap, readily available starting material into a valuable substance, the percentage of the desired intermediate gained at each stage is one of the major factors in judging the economic viability of the synthesis (another major factor is the cost of ridding the final desired product of the inevitable impurities produced by the side reactions).

Properties. Vanillin is a colorless crystalline solid mp 82-83 °C) with a typical vanilla odor. Because it possesses aldehyde and hydroxyl substituents, it undergoes many reactions. Additional reactions are possible due to the reactivity of the aromatic nucleus. Vanillyl alcohol and 2-methoxy-4-methylphenol are obtained by catalytic hydrogenation vanillic acid derivatives are formed after oxidation and protection of the phenolic hydroxyl group. Since vanillin is a phenol aldehyde, it is stable to autoxidation and does not undergo the Cannizzarro reaction. Numerous derivatives can be prepared by etherification or esterification of the hydroxyl group and by aldol condensation at the aldehyde group. Several of these derivatives are intermediates, for example, in the synthesis of pharmaceuticals. 

Veratraldehyde can be prepared by methylation of vanillin. It is used in oriental and warm-woody fragrances, as well as in flavor compositions for vanilla notes. It is an intermediate in, for example, the synthesis of pharmaceuticals. 

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