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.     

Dioxane lignins of kenaf bast and tow

Summary 1. Dioxane lignins have been isolated from the outer (bast) and inner (tow) parts of kenaf of the variety Uzbekskii 15–74, and the semiempirical formulas of the phenylpropane structural units of these dioxanes have been calculated on the basis of elementary and functional analyses.2. It has been shown by measurements of molecular-weight distribution that the DLAKK was more polydisperse than the DLALK.3. A study of the products of alkaline nitrobenzene oxidation and of decomposition by metallic sodium in liquid ammonia has shown that the DLAKK and DLALK were constructed of p-coumaryl, guaiacyl, and syringyl structural units, with the latter predominating.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 74–82, January–February, 1979.     

Establishment of an ester bond in kenaf lignins

Summary Four dioxane lignins from kenaf have been subjected to alkaline hydrolysis, and the presence of esterified p-coumaric and p-hydroxybenzoic acids in them has been shown.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 216–218, March–April, 1979.     

Cleavage by sodium in liquid ammonia of kenaf lignins and the biological activity of the cleavage products

The natural lignin of kenaf stems and fractions of the dioxane lignin of kenaf stems isolated previously were cleaved by sodium in liquid ammonia in order to study their structure. It was established that the kenaf lignins consist of three types of structural units: p-coumaryl, guaiacyl, and syringyl, with a predominance of the guaiacyl types. An antioxidation activity of the monomeric products of the degradation of the kenaf lignins has been found.Institute of the Chemistry of Plant Substances of the Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 738–742, September–October, 1987.     

Cleavage by sodium in liquid ammonia of kenaf lignins and the biological activity of the cleavage products

The natural lignin of kenaf stems and fractions of the dioxane lignin of kenaf stems isolated previously were cleaved by sodium in liquid ammonia in order to study their structure. It was established that the kenaf lignins consist of three types of structural units: p-coumaryl, guaiacyl, and syringyl, with a predominance of the guaiacyl types. An antioxidation activity of the monomeric products of the degradation of the kenaf lignins has been found.     

A study of the phospholipids of kenaf

Summary The fatty-acid composition of the combined phospholipids and also of the main and two minor components of the phospholipids have been studied. On the basis of the results of acid hydrolysis and also IR spectroscopy, the glycerophospholipid structure of the main components of the total material has been confirmed. These main components have been subjected to enzymatic hydrolysis: the position distribution of the fatty acids have been determined and, from these, the possible diglyceride compositions of the phosphatidylcholines, phosphatidylethanolamines, and phosphatidylinositols have been calculated. It has been shown that the phospholipids are accompanied by 35–40% of carbohydrates which have been characterized qualitatively as disaccharides.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 289–293, May–June, 1976.     

A study of the anthocyanins of kenaf

Chemistry of Natural Compounds -     

A CNDO CI study of the electronic structure and spectrum of nitrobenzene

The electronic spectrum of nitrobenzene is investigated by means of the modified CNDO method of Del Bene and Jaffé.     

Mechanistic study of the oxidation of -ascorbic acid by chloranil at the nitrobenzene water interface

The redox reaction between -ascorbic acid in water and chloranil in nitrobenzene has been studied by means of polarography with an ascending water electrode as well as cyclic voltammetry with a stationary interface. Through accurate measurement of the limiting currents, it has been suggested that the redox reaction should be a two-electron reaction rather than a one-electron reaction described previously. A spectrophotometric technique has also been used to observe that the redox reaction proceeds spontaneously under certain conditions even without electrochemical control. Based on these findings, it has been concluded that the present heterogeneous charge transfer reaction is the ion transfer of chloranil semiquinone radical, which is driven by the homogeneous electron transfer between ascorbic acid and chloranil in the aqueous phase.     

A comparative study of the dioxane lignins ofAlthea

Summary 1. The dioxane lignins have been extracted from three species ofAlthea for the first time. On the basis of elementary and functional analyses, the semiempirical formulas of the phenylpropane structural units have been calculated.2. The molecular weight distributions have shown that the DLAs of these species ofAlthea are polydisperse, and in the case of the DLAs of the wild-growing species —A. rhyticarpa andA. nudiflora — the high-molecular weight fraction is predominant, while for the DLA ofA. rosea the low-molecular-weight fraction is predominant.3. In a study of the products of nitrobenzene oxidation it has been established that the DLA of all three species ofAlthea includes p-coumaryl, guaiacyl, and syringyl structural units.4. In the products of decomposition with metallic sodium in liquid ammonia 18 phenols have been identified the structures of which show the presence in the initial lignins of guaiacyl- and syringylpropane units with free OH groups in the side chains in the - and -positions to the aromatic nucleus.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 93–100, January–February, 1977.     

A photoelectrochemical study of the anodic oxidation of lead in alkaline solution

The oxidation of lead in sodium tetraborate and in sulphuric acid solution has been studied. The analysis of photocurrent spectra has shown that tetragonal PbO is formed in both electrolytes. Evidence for photoemission from the metal substrate into the anodic oxide film is presented and discussed. The photocurrent behaviour is related to changes in electrode impedance which accompany the interconvertion of PbO and PbO₂.     

A study of the structure of the dioxiane lignins of the cotton plant of variety 108-F by proton magnetic resonance

Analysis of the PMR spectra of acetylated dioxane lignins of the cotton plant collected in various vegetation periods have shown that the DLAs have different degrees of substitution of the C₃ side chain and different degrees of condensation through the aromatic nuclei. With an increase in the time of extraction of the dioxane lignins from the plant, condensation of the lignins isolated takes place. It has been shown that in the DLAs studied the amounts of -alcoholic hydroxyls are different.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 388–392, May–June, 1979.     

Obtainment of chelating agents through the enzymatic oxidation of lignins by phenol oxidase

Oxidation of lignin obtained from acetosolv and ethanol/water pulping of sugarcane bagasse was performed by phenol oxidases: tyrosinase (TYR) and laccase (LAC), to increase the number of carbonyl and hydroxyl groups in lignin, and to improve its chelating capacity. The chelating properties of the original and oxidized lignins were compared by monitoring the amount of Cu²⁺ bound to lignin by gel permeation chromatography. The Acetosolv lignin oxidized with TYR was 16.8% and with LAC 21% higher than that of the original lignin. For ethanol/water lignin oxidized with TYR was 17.2% and with LAC 18% higher than that of the original lignin.