Reactions of vanillyl alcohol

Figure 2. The reaction of vanillyl alcohol (4) with a reactive phenol (5)-...

This research was undertaken to study aqueous alkaline reactions of monomeric structures, similar to polymeric wood constituents, from which color would be formed. Since hardwood pulps were of the greatest immediate interest, the reaction of syringyl alcohol, representing the hardwood lignin structure, in aqueous alkaline solution at room temperature has been studied extensively up to the present time, but the reactions of vanillyl alcohol and a-methylvanillyl alcohol, representing the softwood lignin structure, have also been studied to some extent under the same reaction conditions. 

Products from the Reaction of Vanillyl Alcohol with Aqueous Alkali. Table VI shows the results of a paper chromatography experiment comparing the R/ values of compounds formed by the reaction of vanillyl alcohol and sodium hydroxide with R/ values of reference com-... 

Table VI. Reaction of Vanillyl Alcohol with Alkali...

The maxima of the spectra of the eluted reference compound, diguaiacylmethane, and of the reaction product are located at almost identical wavelengths for both the neutral solvent and ionization Ac curve, as shown in Table VII. Furthermore, in both cases, the locations of the maxima of the ionization Ac curves agree well with the locations of the maxima of the ionization Ac curve of an ethanolic diguaiacylmethane solution (Table VII). Thus, paper chromatography and spectral analyses indicate that diguaiacylmethane is a product of the reaction of vanillyl alcohol with sodium hydroxide under aqueous reaction conditions. 

Vanillic Acid and Unknowns. The vanillic acid reference spot has an Rf value of 0.39 (Table VI) as does one of the compounds from the reaction mixture. However, as Table VI shows, the colors of these spots, after applying the location sprays, have been recorded as being slightly different. Therefore, although the results so far indicate that vanillic acid might be a product of the reaction of vanillyl alcohol and alkali, spectral analyses of the eluates of the chromatographic spots at the Rf value of 0.39 is necessary for confirmation. 

Table VI also shows that the mixture from the reaction of vanillyl alcohol and alkali contains at least two more unidentified compounds. These are represented by the spots located at the origin and at the Rf value of 0.16. It is possible that more than one compound, represented by the rust color, is located at the origin, but additional experimental work is necessary to verify this fact. These unknown compounds located at the low Rf values could be similar in structure to unknowns IV, V, VI, and VII, discussed previously.

The experimental work involving the determination of products in the reaction of vanillyl alcohol and sodium hydroxide was performed by William B. Mucklow. 

DR Dimmel, D Shepard, TA Brown. The Influence of Anthrahydroquinone and Other Additivies on the Condensation Reactions of Vanillyl Alcohol. J Wood Chem Technol 1 123, 1981. 

Color Characteristics of the Reaction Mixtures. Initial experiments in air involving the reactions of syringyl alcohol, vanillyl alcohol, and a-methylvanillyl alcohol with alkali showed both visually and spectro-photometrically that the reaction mixture of syringyl alcohol, the hardwood lignin model, and alkali was more intensely colored than either of the reaction mixtures of the guaiacyl compounds and alkali. 

Methoxyquinone. Although methoxyquinone has not been definitely established as a product, the experimental work to date strongly indicates its presence. Table VI shows that the reference compound, methoxyquinone, is located at an Rf value of 0.47 and that there is a corresponding compound at the same Rf value from the reaction mixture of vanillyl alcohol and alkali. Both compounds appear as yellow spots on the chromatogram. 

Hastbacka 13) proposed the first stage in the reaction between vanillyl alcohol and aqueous sodium hydroxide as the formation of the quinonemethide from vanillyl alcohol. Subsequently, a molecule of quinonemethide reacts with a molecule of vanillyl alcohol forming diguaiacylmethane. 

Goliath, M., and Lindgren, B. O. (1961). Reactions of thiosulphate during sulfite cooking. Part 2. Mechanism of thiosulphate sulphidation of vanillyl alcohol. Sven. Papperstidn. 64, 469-471. 

TLC analysis of samples was conducted on silica-gel plates carefully spotted with 10-20 pg of standard compounds, and 30 pL of bioconversion reaction samples. Plates developed with 75 25 1 (v/v/v) CH2CI2/CH3CN/HCOOH solvent may be visualized with a 254 nm UV lamp and/or by spraying with a 30 % w/v phosphomolybdic acid/ 95% ethanol spray reagent followed by gentle heating. Rf values of standards are vanillyl alcohol, 0.8 vanillic acid, 0.5 and vanillin 0.4. 

In flavin-dependent monooxygenases, a flavin-oxygen intermediate reacts with the substrate, also producing water in a second step, and requiring cofactors for regeneration of the flavin moiety. The unusual flavoprotein vanillyl-alcohol oxidase (EC 1.1.3.38), in which the flavin moiety is covalently bound, catalyzes the oxidation of p-substituted phenols as well as deamination, hydroxylation and dehydrogenation reactions [10]. 

Aromatic Ring Cleavage of Phenolic 0-0-4 Substructure Model Compounds by Laccase. When vanillyl alcohol was used as a substrate, only biphenyl formation (C5-C5 linked) occurred and no evidence for the formation of any ring-opened products was obtained (26). Hence, we also examined the effect of laccase on the sterically hindered 4,6-di-<-butylguaiacol substrate 50, as it would be unlikely to undergo such free-radical coupling 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. 

Preparation of Reaction Solutions. In general, the reaction solutions of the aromatic alcohols (syringyl alcohol, vanillyl alcohol, and a-methylvanillyl alcohol and their ethers were prepared by adding aromatic alcohol or ether (usually 2.5 X 10-4 mole) to the solvent (water or ethanol) in a 10-ml. volumetric flask. After the model compound was dissolved, the calculated amount of a sodium hydroxide solution was added to make the reaction solution 1 1 molar (model compound to alkali). The solution was then made up to the 10 ml. mark by adding solvent. These solutions were allowed to react at room temperature for given periods. 

The layer of K2C03 separated quantitatively, 0.2 ml of 2% periodate solution was added and the substrate was oxidized at 50°C for 30 min. The reaction was stopped by the addition of 0.2 ml of 10% sodium metabisulphite, the reaction mixture was cooled with water and vanillin was reduced to vanillyl alcohol by reaction with 100 ml of potassium boro-hydride at room temperature for 10 min. The pH was then adjusted to 7.0 with 5 N acetic acid and 0.6 ml of phosphate buffer (pH 7.2) was added. After mixing, the mixture was extracted with two 10-ml portions of ethyl acetate and the extracts were combined and evaporated to dryness at decreased pressure. In order to remove borate, methanol was added and the mixture again evaporated to dryness. The residue was transferred into a small vial with 2 ml of ethyl acetate and was treated with 0.5 ml of trifluoroacetic-anhydride at room temperature for 1 h. The contents of the vial were evaporated to dryness in an evacuated desiccator, the residue dissolved in 1 ml of ethyl acetate and 1 jul analysed on 3% OV-17 at 150°C. 

The 1H-NMR and 13C-NMR spectra were obtained for each of the three components. The spectra of the components are compared with those of methyl xyloside and saligenin in Tables I and II. The spectra are consistent with the three components having been formed by the reaction of one hydroxyl substituent on methyl xyloside with the methylol group of saligenin to form an ether linkage. Formation of similar compounds has been reported on reacting carbohydrates with vanillyl alcohol (12). 

Condensation reactions. The nature of phenyl units and reaction conditions has been shown to influence lignin condensation reaction [311-313]. Syringyl nuclei condensed more readily than guaiacyl nuclei with vanillyl alcohol [311]. Yasuda et al. [312] observed the formation of benzyl chloride on treatments of (3-0-4 dimers in hydrochloric acid this would reduce condensation at the benzyl position. They also observed an intramolecular condensation product of a phenylcoumaran type [313]. This intramolecular condensation was shown to be dominant in an 85% formic acid solution [314,315] and was insignificant in 50% aqueous ethanol containing 0.2 M HCl [306]. 

Vanillyl alcohol yields 93% of vanillic acid on heating with aqueous sodium hydroxide and silver oxide for a few minutes at 75 C. The oxidation most probably involves a Cannizzaro-type reaction [366]. 

A model system for the synthesis of lignin-like polymers showed that jols would react with the quinone-methlde intermediates in this system by a 1-6 addition (J ). Utilizing this model system, chloroanilines were copolymerized with coniferyl alcohol in the presence of horseradish peroxidase Type II enzyme, hydrogen peroxide, vanillyl alcohol initiator and pH 7.2 buffer (J57). The mechanism of this copolymerization reaction is shown in Equation 36. The... 

J Sipila, G Brunow. On the mechanism of formation of non-cyclic benzyl ethers during lignin biosynthesis. Part 2. The effect of pH on the reaction between a (3-0-4-type quinone methide and vanillyl alcohol in water-dioxane solutions. The stability of non-cyclic benzyl aryl ethers during lignin biosynthesis. Holzforschung 45 275-278, 1991. 

The reactions of peracetic acid with p-alkyl and p-hydroxyalkyl phenols can be attribnted to electrophilic reaction of nnionized peracetic acid. Phenol was nnreactive bnt degradation occnrred when methoxyl or other electron donating snbstituents were added. Creosol, gnaiacol, vanillyl alcohol, or apocynol (V) are more readily oxidized at pH near 9, confirming that ionized phenols are more snsceptible than nnionized phenols to electrophilic attack. An observed decline in the rate of reaction above pH 9 can be attribnted to the decreased concentration of peracetic acid dne to ionization to peracetate ions. 

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. 

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