Syringyl phenols

Hristea EN, Covaci-Cimpeanu IC, Ionita G, Ionita P, Draghici C, Caproiu MT, Hillebrand M, Constantinescu T, Balaban AT (2009) Reactions of 2,2-diphenyl-1-picrylhydrazyl (DPPH) with two syringylic phenols or one aroxide derivative. Eur J Org Chem 626-634... 

Vanillyl phenols Syringyl phenols Cinnamyl phenols p-Hydroxyl phenols Sum of phenols ( Lig/g organic carbon) % phenol carbon totd organic carbon ... 

Table XII. The ratio of acid to aldehyde for vanillyl and syringyl phenols from stream, foam, and foam-extract humic substances from Como Creek and the Suwannee River.

High-temperature cupric oxide (CuO) oxidation of vascular plant lignins yields the eight simple phenols illustrated here as major reaction products. These reaction products comprise monomethoxylated (vanillyl) and dimethoxylated (syringyl) phenols, which occur primarily as aldehydes, along with smaller amounts of the corresponding ketones and acids. Two cinnamyl phenols (p-coumaric and ferulic acid) are also produced that retain the three-carbon side chain of the original structural units and terminate in a carboxyl. 

In addition to changes in stable isotope composition, photoreactions also cause decreases in lignin content of DOC [21,145,146]. Such decreases, especially loss (compared to freshwater DOC) of photochemically-sensitive molecular indicators such as syringyl phenols [142], also are observed in coastal DOC samples, indicating that UV-induced oxidation of part of the terrestrial DOC is rapid. 

M Ragnar, CT Lindgren, N-O Nilvebrant. pKa-values of Guaiacyl and Syringyl Phenols Related to Lignin. J Wood Chem Technol 20 277-305, 2000. 

Syringyl/vanillyl ratio (S/V ratio) The S/V ratio is calculated as the concentrations of syringyl phenols divided by the sum of vanillyl phenols. It is a measure of the relative contributions of gymnosperm residues and angiosperm residues to sediment organic matter. 

To ascertain whether syringyl derivatives IV, V, and VI could be converted to phenoxy radicals under biological conditions, we treated water solutions of the phenols with hydrogen peroxide and peroxidase. All three phenols formed transient green species in contrast to the vanillin compounds (which yielded brown precipitates). The aqueous solutions turned red within a few minutes after initial reaction. If these solutions were quickly frozen in liquid nitrogen a few seconds after the reactants had been mixed, a blue solid was obtained. When the solid was examined by EPR spectrometry, radicals were observed whose half-lives were estimated at 30-60 seconds. The radicals appeared to be identical to those generated in benzene. 

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. 

In the course of the previous work we have prepared compounds for comparative purposes, one of which has been reported by Gierer. He and his co-workers 15) synthesized an unsymmetrical diphenylmethane by acid-catalyzed condensation of syringyl alcohol and 2-methoxy-4-methyl-phenol and assumed substitution in the 6-position of the guaiacol nucleus. We repeated this synthesis and prepared an isomeric material by base-catalyzed condensation of the same starting materials. Our interpretation of the modes of synthesis and the NMR spectra of the two compounds is that Gierer s compound most probably is 3, 4-dihydroxy-6 -methyl-3,4, 5-trimethoxydiphenylmethane and that the compound prepared under basic conditions is 2, 4-dihydroxy-5 -methyl-3,3, 5-trimethoxydiphenylmethane, the structure claimed by Gierer. We do not, however, have unequivocal structural evidence and our data are summarized under Experimental. 

Figure 9.45 Eleven dominant phenolic monomers, yielded from the oxidation of lignin using the CuO oxidation method these compounds can be separated into four families p-hydroxyl, vanillyl (V), syringyl (S), and cinnamyl (C) phenols. (Modified from Hedges...

Figure 9.47 Concentrations of acid aldehyde ratios in vanillyl (Ad/Al)v and syringyl (Ad/Al phenols during the subaqueous decay of lignin in vascular plants in a 4-year laboratory incubation study. (Modified from Opsahl and Benner, 1995.)...

Figure 9.48 Lignin-phenol concentrations in (a) water column POC and (b) the syringyl-to-vanillyl (S/V) and cinnamyl-to-vanillyl (C/V) ratios of POC at stations in the Baltic Sea from Lulealven River (Lu) to Baltic proper (Bp)—situated from the head (north) to the mouth (south) of the estuary. Other stations are An = Angermanalven BB = Bothnian Bay BSN = Bothnian Sea north BSS = Bothnian Sea south. (Modified from Bianchi et al., 1997.)...

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