VANILLIN PRODUCTION reduction

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. 

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. 

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]. 

The method is said to be more reproducible than a direct vanillin acylation as uncontrolled losses of this volatile intermediate product are obviated. Esselman and Clagett [187] determined the position of the oxygen atom in the chain of polyfunctional fatty acids. The method is based on the reduction of keto, hydroperoxy, epoxy and carboxyl groups to the corresponding alcohols with LiAlH4, subsequent silylation with BSA and the analysis by GC—MS using OV-1 at 225°C. 

As mentioned previously (Chap. 2.2.2.4.1), the major purpose of the GC-MS analysis of a nitrobenzene or cupric oxide oxidation mixture is to verify the identity of the oxidation products established previously by GC or HPLC analysis, and to elucidate the structure of unknown constituents. For example, GC-MS analysis of the nitrobenzene oxidation mixture of milled bamboo lignin from Phyllostachys pubescence showed unequivocally that compounds (l)-(3) in the total ion chromatogram of the oxidation mixture (Fig. 6.2.2) are indeed p-hydroxybenzaldehyde, vanillin, and syringaldehyde, respectively (Tai et al. 1990) (see Chap. 9.1 for a discussion of the GC-MS technique). In addition, the unknown compound in the chromatogram was identified as p-hydroxyazobenzene (15) (Fig. 6.2.1), one of the phenolic reduction products of nitrobenzene. 

On reduction with sodium borohydride, product II yielded a pair of radioactive products that were tentatively identified as 2-deoxy-L-Zyxo-hexose and 2,6-dideoxy-L-arafeino-hexose. This result, together with the chromatographic properties of II, and its reaction on chromatograms with vanillin-perchloric acid to give a blue color, are consistent with the structure of 2,6-dideoxy-L-Zyxo-hexos-4-ulose (20) for II. This structure is also consistent with the concept that II (20) is, very probably, the precursor of III (19). 

It seemed desirable to point out the connection between these two phenomena— namely, autoxidation and production of ozonides, which at first glance seem to have nothing whatsoever to do with each other. This connection is of practical interest, because it is useful to know that aldehydes, such as anisaldehyde or vanillin, are already present to a considerable extent in the prefabricated state— that is, before the reductive hydrolysis to which the ozonization products are finally submitted with a view to scission of the ozonides formed. 

Examples illustrate the rapidly-growing and promising uses of cydodextrins in various operations the intensification of the conversion of hydrocortisone to prednisolone, the improvement in the yield of fermentation of lankaci-dine and podophyllotoxin, the stereoselective reduction of benzaldehyde to L-phenylacetyl carbinol, and the reduction in toxicity of vanillin to yeast, or organic toxic substances to detoxificating microorganisms. In the presence of an appropriate cyclodextrin derivative (e.g., 2,6-dimethyl-(3-cyclodextrin), lipid-like inhibitor substances are complexed. The propagation of Bordatella pertussis and the production of pertussis toxin therefore increases up to hundred-fold. Cydodextrins and their fatty acid complexes can substitute for mammalian serum in tissue cultures. 

For the synthesis of vanillin itself, there follows, in a separate step, a further enzymatic reduction ofthe carboxylic function. To recover the NADP+, the reaction product is stirred for 7 hours at 30 °C together with glucose in the presence of the arylaldehyde-dehydrogenase from Neurospora crassa and glucose phosphate dehydrogenase. 

Aryl-aldehyde dehydrogenase was purified from Neurospora crassa to remove a dehydrogenase that reduces vanillin to vanillyl alcohol 23). Vanillic acid, isovanillic acid, and PCA were extracted from a fermentation broth with ethyl acetate. Reprecipitation of the isolated products increased the vanillic acid PCA ratio from 1 2 to 2.5 1 (mol/mol). Incubation of the resulting mixture with aryl aldehyde dehydrogenase, NADP, and ATP for 7 h at 30 C resulted in a 92% reduction of vanillic acid to vanillin but only a 33% reduction of PCA to protocatechualdehyde. Vanillin was extracted from the reaction with CH2CI2, affording a product with 10 mol % isovanillin as the only detected contaminant. Based on the concentration of vanillic acid in the fermentation broth, reduction of vanillic acid through purification of vanillin proceeded in 66% overall yield. 

Cantarella et al. (2004) determined the effects of several ehemicals in the three main classes of toxins mentioned above, on subsequent enzymatic hydrolysis and simultaneous saccharifieation and fermentation (SSF) for the production of ethanol by Saccharomyces cerevisiae. Vanillin (0.5 g/1) was found to be the most potent inhibitor in SSF when compared to similar concentrations of 5-HMF and acetic acid. Longer lag phases and the most pronounced reduction in fermentation productivity were found when higher concentrations of acetic acid (i.e. 2 g/1) were used, while levulinic and formic acids at 1 g/1 were found to reduce ethanol production by 38% and 48%, respectively. Efficient and selective removal or substantial dilution of vanillin and the organic acid inhibitors found in steam-exploded hydrolysates were concluded to be the most important pretreatment considerations for improving process productivity. 

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