Anodic methoxylation of cinnamate esters

Abstract

Este trabalho descreve a oxidação eletroquímica do 4-metóxi-cinamato de metila e de outros ésteres metílicos do ácido cinâmico die tri-metoxilado, em solução metanólica neutra ou alcalina. Nos estudos eletroquímicos foram empregadas voltametria cíclica, bem como eletrólises preparativas a potencial ou corrente controlados, em celas de um ou dois compartimentos. A influência de parâmetros tais como densidade de corrente, tipo de cela, material do eletrodo, solvente, concentração do substrato e base foi investigada para o 4-metóxi-cinamato de metila. Os produtos observados foram resultantes de metoxilações nucleares e/ou na cadeia lateral, entretanto com o aumento do número de metoxilas no anel aromático foram observados principalmente produtos referentes à metoxilação no anel aromático. As estruturas dos produtos também dependem do tipo de procedimento empregado no seu isolamento. The present work describes the electrochemical oxidation of methyl cinnamate ring methoxylated derivatives in neutral or basic methanolic solution. In the electrochemical studies cyclic voltammetry and preparative electrolyses under controlled potential or current conditions in divided or undivided cells were used. The influence of current density, cell type, electrode material, solvent, substrate and base concentration was investigated for methyl 4-methoxycinnamate.The products result from aromatic ring and side chain methoxylation, however, nuclear methoxylation products were observed in higher yields when the number of methoxy groups in the aromatic ring was increased. The structure of the products is dependent on the work-up procedures.

Ferricyanide-based analysis of aqueous lignin suspension revealed sequestration of water-soluble lignin moieties

“…The high ferricyanide reactivity of VA and SA was attributed to the inuence of the electro-negative oxygen atom of the methoxy groups on ionization or deprotonation of adjacent phenolic hydroxyl groups as previously reported. [47][48][49] The reactivity of VA and SA also correlated with the reported 47 oxidation potential (E pa ) of their phenolic hydroxyl groups (0.73 and 0.49 V respectively) relative to HBA (0.87). a 100 mL of 0.1 mg mL À1 solution of the substrate were diluted with 100 mL of DI-water prior to the reactions which was initiated by the addition of 10 mL 1% ferricyanide reagent.…”

Free Radical Metabolism of Methyleugenol and Related Compounds

“…30 (All oxidation potentials have been corrected to volts vs the standard hydrogen electrode.) The oxidation potential of 1,2-dimethoxybenzene is reported as 1.69 V, 28 while that for allylbenzene is about 2.6 V. 39 The structurally similar compound (3,4-dimethoxy)methylcinnamate has an oxidation potential of 1.7 V. 42 The oxidation potential of HRP Compounds I and II is about 0.9 V near pH 7.4 depending on the isozyme, 43 which suggests that MEU might be oxidized successfully by HRP.…”

Poly[3-(3,4-dihydroxyphenyl)glyceric Acid] from Anchusa italica Roots

“…The extent of methyl esterification was calculated by comparing the integral intensity of the methyl ester signal (δ 3.85, 0.5 H) to that of the aliphatic proton signal at H1 (δ 5.24, 0.7 H) in a 1 H NMR experiment that included a WATERGATE water suppression routine. The presence of methoxy groups at C3'' and/or C4'' in the aromatic ring is excluded as there are no downfield shifts of the signals of C3'' (δ 145.25) and/or C4'' (δ 144.46), which would be expected from methylation of any of these hydroxyl groups [14,15]. Moreover, the 2D DOSY experiment gave similar diffusion coefficients for the methylated and non-methylated signals.…”

“…HM-AI was further characterized by using different NMR spectroscopy techniques. The 1 H NMR, 13 C NMR, and 2D heteronuclear 1 H/ 13 [11][12][13][14][15]. About 70 % of the carboxyl groups of the polymer chain were methylated (MeO: 13 C, δ 54.86; 1 H, δ 3.85).…”