Syringic acid, oxidation

This type of cement has been further improved by the substitution of -hexyl van ill ate [84375-71-3] and similar esters of vanillic acid [121 -34-6] and/or syringic acid [530-57 ] for eugenol (93—95). These substituted cements are strong, resistant to dissolution, and, unlike ZOE and EBA cements, do not inhibit the polymerization of resin-base materials. Noneugenol cements based on the acid—base reaction of zinc and similar oxides with carboxyhc acids have been investigated, and several promising types have been developed based on dimer and trimer acids (82). 

Laccase (PCL) as well as peroxidases (HRP and SBP) induced a new type of oxidative polymerization of the 4-hydroxybenzoic acid derivatives, 3,5-dimethoxy-4-hydroxybenzoic acid (syringic acid) and 3,5-dimethyl-4-hydroxybenzoic acid. The polymerization involved elimination of carbon dioxide and hydrogen from the monomer to give PPO derivatives with molecular weight up to 1.8 x lO (Scheme 22). - ... 

All cements that contain eugenol inhibit the polymerization of acrylates, and those of EBA-eugenol are no exception. In order to remedy this and other defects, Brauer and his coworkers examined alternatives to eugenol (Figure 9.7). These included the esters of vanillic acid (3-methoxy-4-hydroxybenzoic acid, HV) and syringic acid (3,5-dimethoxy-4-hydroxy-benzoic acid). Both are 3-methoxy-4-hydroxy compounds and are thus chemically related to eugenol and guaiacol. Both are solids and have to be dissolved in EBA where they form satisfactory cements with EBA zinc oxide powder. The vanillate (EBA-HV) cements are the more important. 

Brauer, G. M. Stansbury, J. W. (1984a). Cements containing syringic acid ester-o-ethoxybenzoic acid and zinc oxide. Journal of Dental Research, 63, 137 0. 

Wang et al. (62) reported the oxidative polymerization of a mixture of phenolic compounds in aqueous solution containing mont-morillonlte, illite, and kaolinite, each of which had been mixed with quartz in a 3 7 ratio, and by quartz alone. The mixture of phenolic compounds contained gallic acid, pyrogallol, protocatechuic acid, caffeic acid, orcinol, ferulic acid, p-coumaric acid, syringic acid, vanillic acid, and p-hydroxybenzoic acid. The oxidative... 

The fungal enzyme from R. praticola was able to catalyze the oxidative coupling of pentachlorophenol (PCP) and syringic acid, a representative of phenol carboxylic acids from lignin occurring in HS structures. 

In 2006, International Olive Oil decided to validate a method for phenolic snbstance evalnation and the decision was to validate both a colorimetric and a HPLC method. The HPLC method is the one already validated by the Italian Technical Committee for Fats and Oils, based on the Cortesi s method. Phenolic substances are extracted by means of methanol/water 80/20 and injected on a RP C18 Spherisorb ODS-2 type colnmn, 25x0.46 cm, 5 jm particle size, and the detection is carried out at 280 nm. Syringic acid is used as the internal standard. 27 peaks are separated and identified, enclosing some oxidized forms of aglycones. 

Ikeda R, Uyama H, Kobayashi S (1996) Laccase-catalyzed oxidative polymerization of syringic acid. Macromolecules 29 3053-3054... 

Fusion with Alkali Alone. Alkali lignin was first fused with potassium hydroxide at 180°-190°C. under standard conditions used previously for converting vanillin to vanillic acid (10) and syringaldehyde to syringic acid (14). Under these conditions, protocatechuic and vanillic acids were the chief oxidation products, but over 70% of the lignin was recovered as a lignin-like polymeric product. Longer fusion times helped... 

The presence of syringic acid as the methyl ether ester under all conditions of oxidation and of syringaldehyde and acetosyringone as the methyl... 

S/V = Syringaldehyde + syringic acid/vanillin + vanillic acid, from nitrobenzene oxidation. 

Oxidation of the syringic acid is considered to result in the formation of an unstable semiquinone, which undergoes decarboxylation with concurrent uptake of O2 to form the 2,6-dimethoxy-l,4-benzoquinone (41). The third peak from 475 to 521 ppm, with maxima at 483, 504, and 515 ppm, corresponds to azobenzene nitrogens. These most likely arise from nitrogen to nitrogen coupling reactions between the anilino radicals and free aromatic amino groups in the fulvic acid molecules ... 

Surface plasmon resonance 1000 Surfactants 948, 972 Suzuki coupling 1406, 1424 Sympathomimetic drugs 995 Synergism 889-891 Syringic acid, irradiation of 1079 Syringyl alcohol, catalytic oxidation of 1205, 1208... 

The benzoic acid derivatives such as 4-hydroxybenzoic acid, vanillic acid, and syringic acid are generally synthesized from the corresponding cinnamic acid derivatives by g-oxidation of the propenyl side chain after ester formation with coenzyme A (Fig. 5). 

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