Catalytic nitrobenzene oxidation of lignins

Alkaline nitrobenzene oxidation of hardwood and softwood lignins in the presence of redox and phase-transfer catalysts was studied. The selectivity of oxidation of lignins increased by 1.7 to 1.9 times. A possible mechanism of catalysis is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 3004–3007, December, 1996.     

An iboga alkaloid chemotaxonomic marker from endemic Tabernaemontana ternifolia with antitubercular activity

Abstract

Coronaridine (1) was isolated from the CH₂Cl₂ root extract of Tabernaemontana ternifolia. The structure of 1 was established from 1D- and 2D-NMR and HR-ESIMS experiments, and by comparison with reported spectroscopic data. To date, this is the first report of compound 1 from T. ternifolia, introduced as new Tabernaemontana species from Philippines in 2005 on the basis of morphological characters. Coronaridine, an iboga-type indole alkaloid, has been isolated from over 50 Tabernaemontana species and can thus be inferred as a chemotaxonomic marker of the genus. T. ternifolia has a distinct arrangement of leaves not known in the genus, but is variable in other genera. Its isolation from endemic T. ternifolia establishes its position in the genus and supports the claim that coronaridine is a chemical marker of the genus Tabernaemontana. Interestingly, coronaridine exhibited relatively weak activity against Mycobacterium tuberculosis H₃₇Rv (MIC 82.64?μg/mL) (Rifampicin MIC 0.05?μg/mL).     

Influence of lignin origin on the efficiency of the catalytic oxidation of lignin into vanillin and syringaldehyde

The oxidation of a number of lignin species by molecular oxygen was studied. The selectivity of the process was found to be close to that of the oxidation with nitrobenzene. The influence of lignin origin on the yields of vanillin and syringaldehyde as well as the correlation between the rates of wood delignification and the aldehydes formation are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 375–379, February, 1995.     

Recovery of Vanillin and Syringaldehyde from Lignin Oxidation: A Review of Separation and Purification Processes

Lignin is an underexploited side-stream of pulp and paper industry and biorefineries, being used for energy production at mill site or as low value material for dispersants or binding applications. However, an integrated process of reaction and separation can be implemented for the production of high added-value monomeric phenolic chemicals such as vanillin and syringaldehyde. In this review, the main research advances in the recovery of vanillin and syringaldehyde resulting from oxidation of lignin are addressed, covering various separation methodologies namely liquid-liquid extraction, supercritical fluid extraction, distillation, crystallization, membrane separation, and adsorption. Studies in this area started in the early years of the 20^th century, but in the last decades several processes have been suggested, mainly for vanillin separation. Finding the ultimate industrially feasible process is still a necessary task and this review points out the most promising technologies and sequence of processes.     

Added-Value Chemicals from Lignin Oxidation

Lignin is the second most abundant component, next to cellulose, in lignocellulosic biomass. Large amounts of this polymer are produced annually in the pulp and paper industries as a coproduct from the cooking process—most of it burned as fuel for energy. Strategies regarding lignin valorization have attracted significant attention over the recent decades due to lignin’s aromatic structure. Oxidative depolymerization allows converting lignin into added-value compounds, as phenolic monomers and/or dicarboxylic acids, which could be an excellent alternative to aromatic petrochemicals. However, the major challenge is to enhance the reactivity and selectivity of the lignin structure towards depolymerization and prevent condensation reactions. This review includes a comprehensive overview of the main contributions of lignin valorization through oxidative depolymerization to produce added-value compounds (vanillin and syringaldehyde) that have been developed over the recent decades in the LSRE group. An evaluation of the valuable products obtained from oxidation in an alkaline medium with oxygen of lignins and liquors from different sources and delignification processes is also provided. A review of C₄ dicarboxylic acids obtained from lignin oxidation is also included, emphasizing catalytic conversion by O₂ or H₂O₂ oxidation.     

木素碱性硝基苯氧化产物的高效液相色谱分析

- hydroxybenzaldehyde,vanillin and syringaldehyde etc. were separated on a Novapak C18 column (5μ 3. 9mm i. d.× 150mm) and eluted with MeOH-H2O (25:75, V/V) at a flow rate of 0. 6mL/min and detected at 254nm. Quantitative analysis was performed with piperonal instead of synthetic product . m-meconin,as the internal standard. Recoveries are 95%-98% and CV≤1%. The method is simple,rapid and reliable.