170,078 research outputs found
SINGLET OXYGEN IN THE PHOTODEGRADATION OF LIGNIN MODELS
No full textThe photochemical oxidation of lignin models in the presence of singlet
oxygen nas studied. The treatment of the non-phenolic beta-O-4 aryl
ether derivatives 6, 7, and 8 in the presence of both oxygen and Rose
Bengal gave products deming from a formal beta-C-O cleavage formation.
By this way the derivatives 12. 13, and 15 were obtained, The
photochemical oxidation of the phenolic beta-O-4 aryl ehter 9 gave the
same type of product confirming that, in this case, the presence of the
carbonyl group is not indispensable to have the cleavage reaction. The
use of the model compound 10 showed that. When the phenoxy part of the
molecule shows a lower reactivity towards singlet oxygen, the oxidation
of the phenol moiety to hydroquinone call occur. The photochemical
behaviour of these model compounds can be rationalised from a reaction
of singlet oxygen with the phenoxy part of the molecule. (C) 1997
Published by Elsevier Science Ltd
Photodegradation of lignin: The role of singlet oxygen
No full textThe photochemical irradiation of some phenoxyacetophenone derivatives in
the presence of oxygen by using visible light did not produce any
decomposition product. In the presence of singlet oxygen, sensitized by
using Bengal Rose, decomposition products were obtained. The products
obtained were similar to those obtained by direct beta-C-O cleavage on
the substrate. In this case, the observed behavior can be explained
assuming an attack of singlet oxygen on a phenoxy part of the molecule
Prodotti ad elevato valore aggiunto e nuovi materiali mediante ossifunzionalizzazione selettiva di biomasse
No full textChemistry and materials. Italic 4. Wood, 100 years of structural studies
No full textNonostante la prima caratterizzazione strutturale della lignina risalga al 1908 molto è ancora ignoto circa la struttura dei materiali lignocellulosici. Italic 4 ha dedicato una sessione agli avanzamenti nel settore, focalizzata principalmente sull’identificazione e caratterizzazione di interazioni supramolecolari in biopolimeri vegetali
Reactivity of phenolic and nonphenolic residual kraft lignin model compounds with Mn(II)-peroxidase from Lentinula edodes
No full textOn the role of 1-hydroxybenzotriazole as mediator in laccase oxidation of residual kraft lignin
No full textA novel and efficient catalytic epoxidation of monoterpenes by homogeneous and heterogeneous methyltrioxorhenium in ionic liquids
No full textA convenient and efficient synthesis of monoterpene epoxides by application of methyltrioxorhenium and heterogeneous poly(4-vinylpyridine)/methyltrioxorhenium and microencapsulated polystyrene/methyltrioxorhenium catalytic systems in ionic liquids is described here. It was found that even highly sensitive terpenic epoxides were obtained in excellent yields. Environmentally friendly, easily available and low cost (UHP) urea hydrogen peroxide adduct was used as the primary oxidant. Catalysts were stable systems for at least four recycling oxidations. Experimental results showed that the reactions performed in ionic liquids were more selective and efficient than the ones performed in molecular solvents. (c) 2009 Elsevier B.V. All rights reserved
Catalytic MTO-based C-H insertion reactions of hydrogen peroxide: An investigation on the polymeric support role in heterogeneous conditions
No full textPolymer-supported methyltrioxorhenium (MTO) compounds are shown to act as efficient and selective catalysts for the oxy-functionalization of C-H bonds in representative hydrocarbon derivatives (leading to the corresponding alcohols or ketones), using H2O2 as oxidant. The different supports used for the heterogenation of MTO, such as poly(4-vinylpyridine), poly(4-vinylpyridine)-N-oxide and polystyrene resins, all showed different catalytic behaviour in terms of substrate conversion and product yield, depending on the experimental conditions used. It is noteworthy that the novel heterogeneous catalysts were found to be stable, it being possible to effect their recover and recycle at least five times without appreciable loss of activity
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