A study of the structure of kenaf lignins by alkaline nitrobenzene oxidation

Summary 1. The nitrobenzene oxidation of the natural lignins of kenaf stems and of DLA fractions has been performed. A study of the oxidation products by gas-liquid chromatography has shown that the kenaf lignins are constructed of three types of structural units: p-coumaryl, guaiacyl, and syringyl, with the latter predominating.2. Among the products of the nitrobenzene oxidation of fractions of kenaf dioxane lignin paper chromatography has shown the presence of dihydrodivanillin, which is a representative of structures with a biphenyl bond.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 641–645, September–October, 1978.     

Cotton plant lignins

This paper generalizes the results of studies on lignins isolated from the stems, bolls, and seed hulls of cotton plants of a number of varieties as functions of the vegetation periods of the plants. The UV, IR and¹H and¹³C NMR spectra of the lignins have been studied. The dioxane lignin (DLA) and the natural lignins have been subjected to nitrobenzene oxidation and to cleavage with sodium in liquid nitrogen. A structure of the lignin macromolecules consisting of 18 phenylpropane structural units has been done up. Information is given on the use of lignins in agriculture, the food industry, and the paint and varnish industry. The anticorrosion and sorption properties of hydrolysis and modified hydrolysis lignins have been studied.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 40 64 75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 465–496, July–August, 1997.     

Oxidation in Acidic Medium of Lignins from Agricultural Residues

Agricultural residues as sugarcane straw and bagasse are burned in boilers for generation of energy in sugar and alcohol industries. However, excess of those by-products could be used to obtain products with higher value. Pulping process generates cellulosic pulps and lignin. The lignin could be oxidized and applied in effluent treatments for heavy metal removal. Oxidized lignin presents very strong chelating properties. Lignins from sugarcane straw and bagasse were obtained by ethanol–water pulping. Oxidation of lignins was carried out using acetic acid and Co/Mn/Br catalytical system at 50, 80, and 115 °C for 5 h. Kinetics of the reaction was accomplished by measuring the UV-visible region. Activation energy was calculated for lignins from sugarcane straw and bagasse (34.2 and 23.4 kJ mol⁻¹, respectively). The first value indicates higher cross-linked formation. Fourier-transformed infrared spectroscopy data of samples collected during oxidation are very similar. Principal component analysis applied to spectra shows only slight structure modifications in lignins after oxidation reaction.     

Nitrobenzene oxidation of lignins from several plants of the family Gramineae

It was found based on results from alkaline nitrobenzene oxidation of natural and isolated dioxane lignins from several plants of the family Gramineae such as rice husks, rice straw, and corn and sorghum stems that the studied lignins consisted of three types of structural units with the predominance of guaiacyl structures.     

Isolation of soil lignins by combination of ball-milling and cellulolysis: Evaluation of purity and isolation efficiency with pyrolysis/GC/MS

CuO oxidation is traditionally used for soil lignin study, although, like other degradation methods it might give access only to a part of the lignin polymers. For structural characterization, lignins are conventionally isolated from plant material by combining ball-milling, cellulolysis and solvent extraction to recover a milled wall enzymatic lignin (MWEL) fraction. This method might isolate condensed lignins, which are not accounted for CuO oxidation. MWELs are still associated with polysaccharides. This study aimed to evaluate if the MWEL method can be used complementary to CuO oxidation for soil lignin studies. We assessed the purity of isolated lignins by pyrolytic characterization of MWEL as well as the efficiency of the isolation method by characterization of the MWEL-free residues. MWELs isolated from maize stems and leaves and soil were primarily composed of lignin units, with few associated polysaccharides. MWELs isolated from soils were more degraded and contained less polysaccharides than MWEL from maize tissues. Fewer lignin-derived pyrolysis products were detected in the soil residue compared to the residues obtained from plant tissues. The MWEL method appeared very efficient in isolating relatively pure lignins from soil, most probably because the lignin–polysaccharide complex is less intact than in plants.     

A study of the structure of lignins of healthy and wilt-affected cotton plants of the variety Tashkent-1

Continuing a study of the dioxiane lignins of healthy and wilt-affected cotton plants of variety Tashkent-1 (DLCT) according to vegetation period, we have performed nitrobenzene oxidation and cleavage with sodium in liquid ammonia of the natural and isolated dioxane lignins. It has been established that in the wilt-affected samples of cotton-plant stems the amount of guaiacyl and syringyl structural units increases.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 392–396, May–June, 1979.     

Thermal behaviour of lignins extracted from different raw materials

The thermal degradation of lignins extracted from bagasse, rice straw, corn stalk and cotton stalk, have been investigated using the techniques of thermogravimetric analysis (TG) and differential thermal analysis (DTA), between room temperature and 600°C. The actual pyrolysis of all samples starts above 200°C and is slow. The results calculated from TG curves indicated that the activation energy, Efor thermal degradation for different lignins lies in the range 7.949–8.087 kJ mol^?1. The DTA of all studied lignins showed an endothermic tendency around 100°C. In the active pyrolysis temperature range, thermal degradation occurred via two exothermic process at about 320 and 480°C, and a large endothermic pyrolysis region between 375 and 450°C. The first exothermic peak represents the main oxidation and decomposition reaction, the endothermic effect represents completion of the decomposition and the final exothermic peak represents charring.     

Electrochemical Oxidation of Hydrolytic Lignins in Fluoride-Containing Aqueous Electrolytes

Russian Journal of General Chemistry - Electrochemical oxidation of hydrolytic lignins from different natural sources in fluoridecontaining alkaline and acidic electrolytes was studied. An...     

PMR spectra of the lignins ofCystoseira barbata at different ages

The PMR spectra of the dioxane lignins from the brown algaCystoseira have been studied. It has been established that the lignins isolated from specimens ofCystoseira of different ages have different degrees of substitution of the C₃ side chain and differ in their degree of condensation. The most highly condensed is the dioxane lignin of young specimens ofCystoseira (age up to one year) and the least condensed the Björkman lignin ofCystoseira aged more than three years. All the PMR spectra of preparations of the lignin of the alga under investigation contain the signals of protons present in coumaran structures, their amount being the greatest in the lignins of the youngest samples and decreasing with increasing age of the alga.Odessa Institute of Structural Engineering. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 91–94, January–February, 1983.     

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.     

Use of lignins as components of background electrolyte in capillary electrophoresis

The electrophoretic behavior of two lignins of different compositions, i.e., spruce dioxane lignin and lignosulfonate, is studied. The lignins are shown to affect the electrophoretic behavior of negatively charged analytes, such as carboxylic acids and phenols; their migration time increases. The addition of lignins improves the analytical parameters of phenol quantification by capillary electrophoresis. By means of a simple non-modified capillary, a mixture of six phenols was separated (simple phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, and perchlorophenol) with the high resolution (up to 20) and efficiency [(1–5) × 10⁵ TPM]. The separation of six phenols takes 10 min, the lower limit of the analytical range makes 1 μg/mL, the relative standard deviation does not exceed 3%. The potency for the determination of simple phenol and m-cresol is shown on an example of the Verrukatsid medication within 7 min.     

Solution and solid state13C-NMR of barley straw lignins

Grass lignins are formed by the polymerization of phenoxy radicals and contain a variety of carbon-carbon and carbon-oxygen bonds. They are similar to the hardwood lignins, but differ by containing a substantial proportion of esterified cinnamic acids. Detailed nuclear magnetic resonance studies in conjunction with chemical analysis have given new information on the structure of grass lignins. Milled straw lignins (MSL) from barley were examined by both solution and solid-state (CP/MAS) NMR before and after acetylation. The assignment of the carbon-13 (100 MHz) solution spectra was achieved using model compound data, nuclear Overhauser enhancement (NOE) suppression, and insensitive nuclei enhanced by polarization transfer (INEPT) techniques. The NOE suppression permitted quantitative analysis of lignin, giving information on the ratio of specific carbon atoms. Use of the relaxation agent, chromium acetylacetonate, enabled accumulation of sufficient spectral data to give a spectrum suitable for integration after 90 h. The INEPT technique, which had not previously been used for lignin analysis, was successfully applied to acetylated MSL. This technique increased signal intensities 3–4-fold and simplified the spectrum by inverting methylene carbons and eliminating or inverting quaternary carbons. Comparison of this spectrum with the normal spectrum permitted accurate assignment of quaternary and methine carbons. The solid-state carbon-13 CP/MAS NMR was used to examinein situ lignin and the isolated MSL. The¹³C-CP/MAS spectrum ofin situ lignin shows that cellulose and hemicellulose resonances dominate with little evidence ot the aromatic structure of lignin. the¹³C-CP/MAS of MSL shows reduced carbohydrate resonances and increased aromatic resonances. The extent of modification to the barley straw was estimated and results indicate the presence oflignin-carbohydrate complexes. Detailed information on the nature of the linkages between lignin components and between lignin and carbohydrate components has been obtained from these spectra.     

Oxidation of organosolv lignins in acetic acid

The oxidation of four lignins obtained by organosolv pulping of eucalyptus wood (Acetosolv-eucalyptus Acetosolv lignin [EAL]), sugarcanebagasse (Acetosolv-bagasse Acetosolv lignin [BAL] and in acetone/water/FeCl₃-bagasse acetone/water lignin [BAWL]), and a softwood mixture (Organocell, Munich, Germany) was performed to obtain vanillin, vanillic acid, and oxidized lignin. Experiments were carried out in a cetic acid under oxygen flow using HBr, cobalt(II), and manganese(II) acetates as catalysts. After 10 h the total vanillin and vanillic acid yields were BAL 0.05 mmol, EAL 0.38 mmol, BAWL 0.45 mmol, and Organ ocell 0.84 mmol. Acetosolv lignins are crosslinked, which explains the lower yields in mononuclear products. The reaction volume (Δ V) of this reaction is −817 cm³/mol, obtained in experiments performed under oxygen pressure, showing the high influence of pressure on the oxidation. The major part of the, lignin stays in solution (oxidized lignin), which was analyzed by infrared spectroscopy, showing an increased in carbonyl and hydroxyl groups in comparison with the original lignin. The oxidized lignin can be used as chelating agent in the treatment of effluents containing heavy metals.     

An investigation of the lignins of healthy and wilt-affected cotton plants of variety Tashkent-1 according to the vegetation periods

Summary 1. The dioxane lignins of healthy and wilt-affected cotton plants of variety Tashkent-1 have been isolated and have been studied comparatively in relation to the vegetation period. On the basis of elementary and functional analysis, semiempirical formulas of the dioxane lignins isolated (DLCT-I to -VII) have been determined and it has been established that the dioxane lignins isolated from the wilt-affected plants contain more OCH₃ groups per phenyl-propane structural unit than the lignins of healthy plants.2. The molecular-weight distributions of the dioxane lignins have been studied and it has been shown that all the dioxane lignins isolated are polydisperse, those of the affected plants to a greater degree.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 260–264, March–April, 1978.     

Lignins from annual grassy plants

Lignins isolated from the annual grassy plants oats Avena sativa, rye Secale sp., wheat Triticum sp., and barley Hordeum sp. were characterized chemically. It was found that the grassy lignins belonged to a class of compositionally heterogeneous GSH-type biopolymers and consisted of monomeric units of the guaiacyl, syringyl, and p-coumaryl types.     

Thermal decomposition and glass transition of industrial hydrolysis lignin

Thermal properties of industrial hydrolysis lignin (HL) obtained from bio-ethanol production plants were investigated by thermogravimetry and differential scanning calorimetry. Thermal decomposition of HL was observed in two stages suggesting coexisting carbohydrates. Glass transition temperature (T _g) was observed in a temperature range from 248 to 363 K. T _g values were lower than that of other industrial lignins, such as kraft lignin or lignosulfate. Enthalpy relaxation was observed as sub-T _g, which is not as prominent as other industrial or laboratory scale isolated lignins. T _g of HL decreased in the presence of water and saturated at water content (W _c) of 0.18 (mass of water/mass of dry HL). The amount of bound water calculated from melting enthalpy of water and W _c was ca. 0.18. Thermal decomposition and molecular motion of as obtained industrial HL are affected by coexisting carbohydrates.     

Infra-red spectroscopic study of lignins

Infra-red spectra from 200–4000cm⁻¹ of lignin precipitated from black liquor produced from different pulping processes of bagasse, e.g. soda, kraft, sulfite, peroxyacid and butanol, have been characterized. Peroxyacid lignins are more degraded than other lignins. However, peroxyacid lignin has a higher intensity band at 1720cm⁻¹ than other types of lignins. At the same time, the aromatic ring of lignin produced from peroxyacid pulping of bagasse undergoes severe degradation. Syringyl type of lignin is predominant in all isolated lignins. Peroxyacid and butanol lignins have lower quantities of syringyl lignin shown by the lower ratio of relative absorbance of band intensity at 1500cm⁻¹ to the band at 1600cm⁻¹ than other lignins. Kraft lignin has a broad weak band at about 630cm⁻¹ that is probably due to a C---S bond. A sharp band at 655cm⁻¹, which is due to SO₃H, is characteristic of lignosulfonate, which is precipitated from black liquor produced from sulfite pulping process of bagasse. Generally, degradation of different lignins during pulping of bagasse with different processes has the following sequence: peroxyformic > peroxyacetic > butanol-water > butanol-alkali > kraft > sulfite > soda.     

On the Role of Retroaldol Reaction in the Process of Lignin Oxidation into Vanillin. Kinetics of the Vanillideneacetone Cleavage in Alkaline Media

Kinetics and selectivity of the retroaldol reaction of vanillideneacetone in the alkaline media were studied. The reaction is of first order with respect to substrate and alkali concentration. The pH dependencies of the rates of vanillin formation in the processes of lignosulfonates and vanillideneacetone oxidation agree almost quantitatively. This indicates that the retroaldol reaction plays an important role in the alkaline oxidative destruction of lignins.     

Analytical methodology for sulfonated lignins

There is a significant need to characterize and classify lignins and sulfonated lignins. Lignins have so far received a good deal of attention, whereas this is not true for sulfonated lignins. There is a clear demand for a better understanding of sulfonated lignins on a chemical as well as physical level. Many of the analytical methods have been developed with different goals in mind, for example, detection of sulfonated lignins in pulp‐mill effluents, elucidation of structural changes in lignosulfonates during a pulping process, or identification of properties that may affect a formulation when sulfonated lignins are used as a dispersant. When sulfonated lignins are used in industrial applications, analytical data obtained using different techniques may be necessary to enable prediction of their behavior in the target application. In the present review, a critical discussion of established and promising analytical techniques for the characterization of sulfonated lignins is presented.     

Chemical,Thermal and Antioxidant Properties of Lignins Solubilized during Soda/AQ Pulping of Orange and Olive Tree Pruning Residues

Some agroforestry residues such as orange and olive tree pruning have been extensively evaluated for their valorization due to its high carbohydrates content. However, lignin-enriched residues generated during carbohydrates valorization are normally incinerated to produce energy. In order to find alternative high added-value applications for these lignins, a depth characterization of them is required. In this study, lignins isolated from the black liquors produced during soda/anthraquinone (soda/AQ) pulping of orange and olive tree pruning residues were analyzed by analytical standard methods and Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (solid state ¹³C NMR and 2D NMR) and size exclusion chromatography (SEC). Thermal analysis (thermogravimetric analysis (TGA), differential scanning calorimetry (DSC)) and antioxidant capacity (Trolox equivalent antioxidant capacity) were also evaluated. Both lignins showed a high OH phenolic content as consequence of a wide breakdown of β-aryl ether linkages. This extensive degradation yielded lignins with low molecular weights and polydispersity values. Moreover, both lignins exhibited an enrichment of syringyl units together with different native as well as soda/AQ lignin derived units. Based on these chemical properties, orange and olive lignins showed relatively high thermal stability and good antioxidant activities. These results make them potential additives to enhance the thermo-oxidation stability of synthetic polymers.