Reaction of syringyl alcohol with alkali

Effect of Oxygen on the Reaction of Syringyl Alcohol with Alkali. Ethanolic solutions of syringyl alcohol (0.0545M in 5 ml.) and sodium hydroxide (0.0923M in 5 ml.) were placed separately in each leg of an inverted Y-tube. After the system was exhaustively evacuated, the solutions were mixed and allowed to react at room temperature. For comparison, an identical experiment was conducted in the presence of air. 

Effect of Oxygen on the Reaction of Syringyl Alcohol with Alkali. Preliminary experiments 18) on the reaction of white birchwood meal with alkali in the presence and absence of oxygen indicated that in the presence of oxygen a red-brown color was formed while in its absence (total pressure 1 X 10-4 mm.), the reaction mixture was yellow-brown. 

Products from the Reaction of Syringyl Alcohol with Aqueous Alkali. Table I shows the locations on the paper chromatogram of products from the reaction of syringyl alcohol with alkali in aqueous medium. The chromatograms were developed using a modified FR-L II system (see Experimental), and the Rf values were compared with the Rf values of reference compounds also shown in Table I. 

Table I. Reaction of Syringyl Alcohol with Alkali...

After the reaction product at the Rf value of 0.40 was eluted with water from the chromatogram, its spectrum in neutral solvent and its ionization Ac curve were recorded. The neutral spectrum and the ionization Ac curve of bis-4-hydroxy-3,5-dimethoxyphenylmethane in 47.5% ethanol were also recorded the wavelengths of the ultraviolet absorption maxima of the two compounds—eluted product and reference compound—are given in Table II. The spectra of the compounds possess maxima at nearly identical wavelengths. Thus, paper chromatography and ultraviolet spectroscopy indicate positively that bis-4-hydroxy-3,5-dimethoxyphenylmethane is a product of the reaction of syringyl alcohol with alkali in aqueous solution. 

In addition to the products discussed above, Table I shows that there are other reference compounds for which there are no corresponding reaction products. Experimental evidence has indicated that 3,3, 5,5 -tetra-methoxy-4,4 -diphenoquinone (coerulignone), 4,4 -dihydroxy-3,3, 5,5 -tetramethoxystilbene and 2,6-dimethoxyphenol are not products of the reaction of syringyl alcohol with alkali while additional experimental work... 

A modification of Sawicki s method (22) was used to help prove that 2,6-dimethoxyquinone was a product of the reaction of syringyl alcohol with aqueous alkali. The coupling of the quinone and 1-ethylquinaldinium iodide to form a dye, measured by spectral absorption in the 725 m/x region, was done as follows. 

Syringaldehyde. Table I shows that the reference compound, syringaldehyde, is located at an Rf value of 0.58 and that one of the products of the reaction of syringyl alcohol with aqueous alkali is also located at the same Rf value. These compounds were located on the chromatograms most easily using a long wave ultraviolet lamp after applying the location sprays, and they appeared as violet spots under these conditions. 

At present the only colored product that has been identified in the reaction of syringyl alcohol with aqueous alkali is 2,6-dimethoxyquinone. No evidence exists that dimeric chromophoric structures such as a dipheno-quinone or a stilbenequinone, which have been found to be products in the oxidative reactions of phenols in other studies (/, J, I5y 23), are also products of this reaction. However, with the identification of 2,6-dimethoxyquinone and the two colorless products, bis-4-hydroxy-3,5-dimethoxyphenylmethane and syringaldehyde, one of the logical pathways for the reaction is suggested and discussed. 

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. 

The color characteristics of the reaction mixtures in aqueous and ethanolic solutions were also interesting. In ethanol, the mixture of syringyl alcohol and alkali turned pale violet within 15 minutes after preparation, and the color slowly became more intense with time until a deep violet color was formed, which persisted for approximately 2 months after this time, the violet color slowly faded, and the solution became brown. Concomitant with the appearance of the brown color, a brown polymeric substance settled out of solution. The same reaction mixture in aqueous medium turned yellow in about 15 minutes and then slowly changed to... 

The validity of the reaction presented in Scheme II has been partially proved at this time. When bis-4-hydroxy-3,5-dimethoxyphenylmethane reacts with aqueous alkali under conditions similar to the reaction between syringyl alcohol and aqueous alkali in this study, 2,6-dimethoxyquinone and syringaldehyde are found amTong the reaction products. 

---