Hydrogenolysis of rice husk lignin. IV

The hydrogenolysis of rice husk protolignin and of rice husk hydrolysis lignin in the presence of catalyst D-101, which is used in the hydrocracking of petroleum, has been studied. A substantial amount of products with syringyl structures has been found in the lignin cleavage products. The hydrogen content of the hydrol lignins isolated was considerably higher than that of the analogous lignins obtained on hydrogenolysis with the use of other catalysts. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan. Scientific-Research Chemical and Technical Institute of the Medical and Microbiological Industry, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 602–605, July–August, 1993.     

Hydrogenolysis of rice husk protolignin. II

It has been established that the partial hydrogenolysis of rice husk protolignin (RHP) takes place at a temperature of 180°C and an initial hydrogen pressure of 10 atm in an alkaline medium. Conditions have been selected under which the greatest yield of low-molecular-weight products (91% on the Komarov lignin) is obtained: hydrogenolysis in an alkaline medium in the presence of an anthraquinone (AQ) catalyst. The addition of AQ increases the yield of low-molecular-weight products by a factor of 1.8. Semiempirical formulas have been derived for incompletely hydrolyzed lignin residues. A study of the molecular-weight distribution of these lignins has shown that they are polydisperse. It has been established that in the process of hydrogenolysis AQ promotes the demethoxylation of structural units with syringyl nuclei.Institute of the Chemistry of Plant Substances of the Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 734–738, September–October, 1987.     

Hydrogenolysis of rice husk lignins

The hydrogenolysis of the protolignin, the hydrolysis lignin, and the dioxane lignin of rice husks in the presence of demethylated lignin as catalyst has been studied. The breakdown of the lignins into low-molecular-mass compounds took place with yields comparable with those obtained by hydrogenolysis using other catalysts.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 611–613, July–August, 1995. Original article submitted November 21, 1994.     

Hydrogenolysis of rice husk protolignin. II

It has been established that the partial hydrogenolysis of rice husk protolignin (RHP) takes place at a temperature of 180°C and an initial hydrogen pressure of 10 atm in an alkaline medium. Conditions have been selected under which the greatest yield of low-molecular-weight products (91% on the Komarov lignin) is obtained: hydrogenolysis in an alkaline medium in the presence of an anthraquinone (AQ) catalyst. The addition of AQ increases the yield of low-molecular-weight products by a factor of 1.8. Semiempirical formulas have been derived for incompletely hydrolyzed lignin residues. A study of the molecular-weight distribution of these lignins has shown that they are polydisperse. It has been established that in the process of hydrogenolysis AQ promotes the demethoxylation of structural units with syringyl nuclei.     

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.     

Oxidation of lignin in aqueous alkaline solution

Conclusions The hydrogenolysis and hydrolysis of lignin in an aqueous alkaline medium must be considered as an oxidative degradation of the lignin macromolecule by hydroxyl radicals. This process takes place even in a reducing medium in the presence of a catalyst. This was shown by a study of the hydrogenolysis process using model compounds. The oxidative processes in lignin are connected with the appearance in the system (lignin or its model) of alkali-induced quinoid structures which, being electron-acceptors, abstract electrons from hydroxyl ions and form hydroxyl radicals. The latter lead to oxidative processes through the the hydroxylation of the system. The correctness of this has been confirmed by studying the composition of the products, which shows the oxidative nature of the hydrogenolysis process.Scientific-Research Institute for the Chemistry and Technology of Cotton Cellulose, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 512–517, September–October, 1970.     

Change in the structural elements of cotton-plant lignins in the various vegetation periods

Summary 1. The dioxane lignins of the cottonplant of various vegetation periods have been studied, and it has been shown that the lignin changes in the course of the development of the plant: the amount of methoxy groups increases and the amount of phenolic hydroxy groups decreases.2. Gel chromatography of the lignins has shown that they are all polydisperse with a predominance of the high-molecular-weight fraction.3. The 3,4-diethoxybenzaldehyde detected in the products of the alkaline nitrobenzene oxidation of dioxane lignin of the early vegetation period after its ethylation with diethyl sulfate is a direct proof of the presence of catechol structural units in cotton-plant lignin.4. A quantitative determination of the catechol structures in the lignins of the cottonplant has shown that their amount decreases as the plant develops.5. By decomposing the lignins with sodium and liquid ammonia, the presence in them of guaiacyl, syringyl, and p-coumaryl structural units has been confirmed and it has been shown that the lignin becomes less condensed as the plant grows, which is apparently connected with an increase in the degree of its methoxylation.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 100–107, January–February, 1977.     

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.     

Hydrogenolysis of Willst?tter lignin

Summary 1. The hydrogenolysis of Willstätter spruce lignin has been performed under the optimum conditions. It has been shown that on hydrogenolysis in an aqueous alkaline medium in the presence of an inhibitor (phenol) the lignin macromolecules can be converted into low-molecular-weight ether-soluble products with a yield of about 80%.2. A comparative study of the ether-soluble fractions of Willstätter spruce lignin and hydrolysis spruce lignin has shown that hydrogenolysis takes place similarly in the two cases: the yields of phenols and the proportion of cresols in them are similar. In the Willstätter spruce lignin, the yield of acids is higher and that of neutral products lower than in the hydrolysis spruce lignin.3. Investigations of the group compositions of the hydrogenolysis products and of model substances have permitted the hypothesis that the Willstätter lignin contains a considerable amount of biphenyl structures.Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 106–112, January–February, 1972.     

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.     

Functional composition and IR spectra of cottonseed husk hydrolysis lignin and its derivatives

The functional compositions of cottonseed husk hydrolysis lignin and its derivatives have been determined and their IR spectra have been studied. A possible formation of stronger hydrogen bonds in derivatives of hydrolysis lignin has been shown.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. 3, pp. 392–397, May–June, 1999.     

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.     

Hydrogenolysis of the protolignin from rice husks. III

The hydrogenolysis of the protolignin of rice husks in the presence of a polymetallic catalyst that is used in the hydrocracking of petroleum has been investigated. The dependence of the yield of low-molecular-mass compounds on the reaction conditions has been found. It has been established on the basis of experiments with model compounds that on hydrogenolysis with the use of the polymetallic catalyst both alkyl-aryl C-O-C and C-C bonds are cleaved.Institute of Chemistry of Plant Substances, Academy of Science of the Uzbek SSR, Tashkent. All-Union Scientific-Research Chemical and Technological Institute of the Medicinal and Microbiological Industry, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 679–683, September–October, 1990.     

The lignin of the sea island cotton plant of variety S-6030 affected by fusarial wilt. I

A comparative study of the dioxane lignins isolated from healthy and wilt-affected cotton plant stems has shown thatFusarium fungi demethylate lignin and make it more oxidized than the lignin from healthy stems.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 825–827, November–December, 1985.     

Sorption of polar components of cottonseed oil by hydrolysis lignins and modified lignins

The sorption activities of hydrolysis lignins from wood and from rice and cottonseed hulls and of modified lignins relative to the polar components of crude cottonseed oil in a nonpolar solvent have been studied.Institute of Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 414–416, May–June, 1991.     

Reductive cleavage by metallic sodium in liquid ammonia of cotton lignin

Twofold cleavage with sodium in liquid ammonia of the dioxane lignin and fourfold cleavage of the native lignin from cotton stems have shown that the uncleaved parts of lignin have molecular masses 2–4 times lower than the initial lignins and consist of 15–17 phenylpropane structural units.Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 412–416, May–June, 1989.     

Lignin of the fine-fibered cotton plant of variety S-6030 affected by fusarial wilt. II

A comparative study of the products of cleavage by sodium in liquid ammonia of the dioxane lignins (DLAs) from healthy and fusarial-wilt-affected stems of the fine-fibered cotton plant of variety S-6030 and a study of the PMR spectra of both lignins has shown that the DLA from the healthy stems is more highly condensed than the DLA of the stems affected by wilt. The main structures of DNA wilt are of the guaiacyl type. In the DLA from the affected stems, the amount of p-coumaryl structures had increased, which confirms the demethylating action of fusarial wilt on cotton-plant lignin.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 364–366, May–June, 1986.     

Study of the lignin of cotton plants of the variety AN Bayaut-2. I

The dioxane lignin has been isolated from ripe stems of a cotton plant of the variety AN Bayaut-2. Its developed empirical formula has been derived, its UV, IR, and PMR spectra have been recorded, and its molecular weight has been determined. It has been shown that the dioxane lignins of the stems of cotton plants of different varieties differ in chemical structure.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 101–104, January–February, 1986.     

Sulfomethylation of lignins

Water-soluble derivatives have been obtained by the sulfomethylation of technical lignins. Their semiempirical formulas have been calculated and the introduction of a sulfomethyl group into the lignin macromolecule is discussed on the basis of these formulas.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. 2, pp. 222–225, March–April, 1998.     

Refinement of the structure of asperumine

Summary 1. Asperumine has been isolated from the combined alkaloids ofSymphytum caucasicum.2. The hydrolysis and hydrogenolysis of asperumine has given heliotridine, acetone, and angelic and asperuminic acids.3. The structure of asperumine has been refined on the basis of the products of hydrolysis and hydrogenolysis and also of features of the mass and NMR spectra.4. It has been established that asperumine is an isomer of heliosupine in the 2,3,4-trihydroxy-2-methylpentane-3-carboxylic acid moiety.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 478–480, July–August, 1974.