Vanillin reduction

FIGURE 13.14 Reduction kinetics of vanillin reduction by TBAB at various pH and temperature. (From Pellerin, C., Pedneault, C., and Roberf S., J Pulp Paper Sci, 26(12), 436 0, 2000.)... 

Reduction Products. Glyoxyhc acid [298-12 ], HOOCCHO, mol wt 74.04, is produced as aqueous solution by the electrolytic reduction of oxahc acid. It is used for the manufacture of vanillin. 

Reduction of vanillin by means of platinum black in the presence of ferric chloride gives vanillin alcohol in excellent yields. In 1875, Tiemann reported the reduction of vanillin to vanillin alcohol by using sodium amalgam in water. The yields were poor, however, and there were a number of by-products. High yields of vanillin alcohol have been obtained by electrolytic reduction. 

Vanillin, being an aldehyde, is able to form acetals and hemiacetals. Therefore, in flavor formulations using high concentrations of vanillin in conjunction with carriers such as propylene glycol, a glc analysis often shows a reduced vanillin peak after storage of the compounded flavor, and the presence of new peaks indicating acetal formation. Addition of about 0.5% of water to the formula reverses the reaction, ie, there is a reduction of acetal, and the reappearance of vanillin peaks. 

Guaiacols. Cresote, obtained from the pyrolysis of beechwood, and its active principles guaiacol [90-05-1] (1) and cresol [93-51-6] (2) have long been used ia expectorant mixtures. The compounds are usually classed as direct-acting or stimulant expectorants, but their mechanisms of action have not been well studied. Cresol is obtained by the Clemmensen reduction of vanillin (3), whereas guaiacol can be prepared by a number of methods including the mercuric oxide oxidation of lignin (qv) (4), the ziac chloride reduction of acetovanillone (5), and the diazotization and hydrolysis of o-anisidine (6). 

Monsanto s commercial route to the Parkinson s drug, L-DOPA (3,4-dihydroxyphenylalanine), utilizes an Erlenmeyer azlactone prepared from vanillin. The pioneering research in catalytic asymmetric hydrogenation by William Knowles as exemplified by his reduction of 24 to 25 in 95% ee with the DiPAMP diphosphine ligand was recognized with a Nobel Prize in Chemistry in 2001. ... 

Reductive amination of vanillin with ammonia leads to benzylamine 94. Acylation of that compound with (Z)-9-octadecenoyl chloride affords the analgesic olvanil (95) [23]. 

The reduction of vanillin by the Clemmensen method using toluene as an auxiliary solvent has been reported.3 By following these directions, a yield of 49% of creosol was obtained with large amounts of tar. 

Creosol (also called 2-methoxy-jb-cresol, 4-methylguaiacol, and 3-methoxy-4-hydroxytoluene) has been obtained by the fractionation of beach creosote tar,4 by the reduction of vanillin by electrolytic methods,6 6 by hydrogen and palladium on charcoal or barium sulfate,7 8 with hydrazine,9 and by amalgamated zinc and hydrochloric acid.3 10 11 It has also been prepared by methyl-ation of 4-methylcatechol with methyl iodide 12 13 or with methyl sulfate 14 and is reported to be formed by the distillation of the calcium salt of 3-methoxy-4-hydroxyphenylacetic acid.16... 

The reduction of vanillin has been studied by the FR polarographic technique.107 The FR summit peaks are conspicuous up to 200-250 Hz at all pH s. With an increase in pH, the FR summit peak potential tends to be more cathodic. The FR wave is invariably obtained on the negative side of the abscissa, indicating that a is less than 0.5. The FR polarograms at pH 10.5 are shown in Fig. 31. 

The reduction of vanillin is accompanied by a two-electron charge transfer and the mechanism of the reaction can be explained as follows ... 

The biocatalytic reduction of carboxylic acids to their respective aldehydes or alcohols is a relatively new biocatalytic process with the potential to replace conventional chemical processes that use toxic metal catalysts and noxious reagents. An enzyme known as carboxylic acid reductase (Car) from Nocardia sp. NRRL 5646 was cloned into Escherichia coli BL21(DE3). This E. coli based biocatalyst grows faster, expresses Car, and produces fewer side products than Nocardia. Although the enzyme itself can be used in small-scale reactions, whole E. coli cells containing Car and the natural cofactors ATP and NADPH, are easily used to reduce a wide range of carboxylic acids, conceivably at any scale. The biocatalytic reduction of vanillic acid to the commercially valuable product vanillin is used to illustrate the ease and efficiency of the recombinant Car E. coli reduction system." A comprehensive overview is given in Reference 6, and experimental details below are taken primarily from Reference 7. 

Most of the vanillic acid was reduced by E. coli containing Car in 2 h to vanillin (80 %) and vanillyl alcohol (20 %). Car does not reduce aldehydes to alcohols. However, E. coli s endogenous aldehyde reductase/dehydrogenase reduces vanillin to vanillyl alcohol. The broad substrate specificity of Car enables the wide application of this biocatalyst to other important applications, such as enantiomeric resolution of isomers such as ibuprofen and the reductions of many other natural and synthetic carboxylic acids. 

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]. 

Reduction. The reductive capacity of P. chrysosporium has been known for a long time. For example, veratraldehyde, veratric acid, vanillin, vanillic acid and analogous structures were converted into the corresponding... 

The impact of MOX upon reductive odors was included in the study of McCord (2003) for MOX at 5-10 mL/L/month over 5 months on a Cabernet Sauvignon wine in commercial scale tanks. Lower concentrations of methyl mercaptan and ethyl mercaptan were observed in the oxygenated wines, but no impact was seen upon disulfides, in spite of the suggestion that concentrations of the disulfides could increase due to direct oxidation of sulfides. Dimethyl sulfide concentrations were not affected, except that lower concentrations were seen in wines with added toasted oak staves or segments, with or without MOX. The concentrations of various oak extracted compounds were also measured in this study, with similar levels seen with and without MOX alongside appreciable increases due to the presence of the oak staves or segments in some cases (e.g., lactones and vanillin), oxygenation appeared to enhance aroma extraction. 

Although many substances have been produced by oxidation methods anthraquinone, vanillin, saccharin oxidation is not so easily graduated as the reduction processes. The overvoltage of oxygen is relatively high at most anodes, and frequently the compound to be oxidised is decomposed during treatment and carbon dioxide formed. 

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