Discoloration of α-Carbonyl-Free Lignin Model Compounds Under UV Light Exposure

Castellan, Alain; Colombo, N.; Nourmamode, Aziz; Zhu, Jonathan J. H.; Lachenal, Dominique; Davidson, R. S.; Dunn, L. A.

doi:10.1080/02773819008050252

Cited by 54 publications

(10 citation statements)

References 26 publications

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“…trans-3,3',4,4'-Tetramethoxystilbene (trans-1) and trans-4-hydroxy-3,3',4'-trimethoxystilbene (trans-2) were synthesized according to the method of Castellan et al (8). They exhibited melting points (trans-1; mp 154.6-155.0°C; trans-2; mp 129.6-130.1°C) and spectroscopic data that were similar to the reported data in both cases.…”

Section: Methodsmentioning

confidence: 99%

“…Castellan et al have described qualitative results from the irradiation of several model compounds of this general type, stilbenes, benzofurans, biphenyls, diarylmethanes, and alkenylphenols, adsorbed on filter paper and in solution (8). This study was confined to measurements of the rates of photoinduced discolouration of the paper as a function of adsorbate and photolysis time.…”

Section: Introductionmentioning

confidence: 99%

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The photochemistry of 3,3′,4,4′-tetramethoxy-and 4-hydroxy-3,3′,4′-trimethoxystilbene — models for stilbene chromophores in peroxide-bleached, high-yield wood pulps

Leigh¹,

Lewis²,

Lin³

et al. 1996

Can. J. Chem.

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The photochemistry of the title compounds has been investigated in ethanol and tetrahydrofuran solution under aerobic and anaerobic conditions. Direct irradiation of trans-3,3',4,4'-tetramethoxystilbene (tra~zs-1) in deoxygenated ethanol leads to the rapid establishment of a photostationary state with the cis isomer, and the slower formation of the ethyl ether corresponding to addition of ethanol across the olefinic C=C bond and cyclobutane dimers. The same products are formed upon photolysis in the presence of oxygen under the same conditions but, in addition, two isomeric tetramethoxyphenanthrenes and 3,4-dimethoxybenzaldehyde are formed. Photolysis of trans-1 in oxygenated tetrahydrofuran leads to the same products in different relative yields. Quantum yields for cis,rra~ls photoisomerization, phenanthrene formation, and addition of ethanol have been determined by ferrioxalate actinometry. Direct irradiation of trans-4-hydroxy-3,3',4'-trimethoxystilbene (tratls-2) in ethanol solution also results in rapid cis-tra~ls isomerization and the formation of (three) isomeric phenanthrene derivatives in photolyses carried out in the presence of oxygen, although the material balance is low. The various products of photolysis of trans-2 have been independently synthesized by desilylation of the products isolated from photolysis of trclns-4-tertbutyldimethylsiloxy-3,3',4'-trimethoxystbene (trans-3) under similar conditions. Fluorescence-quenching experiments have been carried out to determine the relative rates of quenching of the excited singlet states of trans-1 and tmtzs-2 by alcohols and oxygen. The formation of aldehydes is proposed to arise via reaction of superoxide ion with stilbene radical cations, which are formed by electron-transfer quenching of the stilbene excited singlet state by oxygen.Key words: stilbenes, lignin, photochemistry, photooxidation.RCsumC : On a CtudiC la photochimie des composCs mentionnks dans le titre en solutions dans 1'Cthanol et le titrahydrofurane, dans des conditions tant akrobiques qu'anakrobiques. L'irradiation direct du tmtzs-3,3',4,4'-tCtramkthoxystilbkne (tratzs-1) dans de 1'Cthanol dCsoxygCnC conduit h la crCation rapide d'un Ctat photostationnaire avec l'isomere cis et h une formation plus lente de l'tther Cthylique correspondant ii l'addition de 1'Cthanol sur la double liaison C=C olCfinique ainsi que des dimkres cyclobutanes. Les m&mes produits se forment lors de la photolyse dans les m&mes conditions, en prCsence d'oxygkne; toutefois, il se forme de plus deux tCtramtthoxyphCnanthrbnes isomkres ainsi que du 3,4-dimCthoxybenzaldthyde. La photolyse du tratzs-1 dans du titrahydrofurane oxygCnC conduit h la formation des m&me produits avec des rendements relatifs diffkrents. On a dCterminC les rendements quantiques de la photoisomCrisation cis, trans, de la formation du phknanthrkne et de l'addition de l'tthanol par actinomCtrie feriioxalate. L'irradiation directe du tmrzs-4-hydroxy-3,3',4'-trimCthoxystilbbne (trans-2) en solution dans 1'Cthanol effectuke en prtsence ...

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The photochemistry of 3,3′,4,4′-tetramethoxy-and 4-hydroxy-3,3′,4′-trimethoxystilbene — models for stilbene chromophores in peroxide-bleached, high-yield wood pulps

Leigh¹,

Lewis²,

Lin³

et al. 1996

Can. J. Chem.

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“…Wengert (1966) (Dirckx et al, 1992 (fig 21 a) Vincent, 1964;Leary, 1967;Dirckx, 1988) que sur les pâtes à papier mécanique (Nolan et al, 1945) ou chimique (Claesson et al, 1967), sur le papier (Leary, 1968a et b;Lenest et al, 1982) et surtout sur des modèles de lignine (Lin et Brunow et Eriksson, 1971;Brunow et Sivonen, 1975; Pettersson, 1975 et (Dirckx, 1988;Dirckx et al, 1992). Les (Leary, 1968 Le rôle des phénols dans la photodégra-dation des lignines n'est pas encore clairement élucidé (Castellan et al, 1990;Heitner et Schmidt, 1991). L'étude de la photolyse en solution des molécules modèles des lignines a montré que la pré-sence de groupes phénoliques libres n'est pas nécessaire pour induire une forte coloration (Scalbert et al, 1987); -la structure des lignines : la structure des lignines de feuillus contient un nombre plus important d'unités syringyles (Nimz, 1974) alors qu'il y a beaucoup plus de gaïacyls pour les résineux (Adler et Marton, 1959;Adler, 1977 (Hon et Ifju, 1978 (Wengert, 1968;Schmitt, 1984 (Dirckx, 1988 (Bergman, 1969) (Dirckx, 1988;Dirckx et al, 1992) …”

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Modification de couleur du bois de chênes européens exposés à la lumière solaire

Mazet¹,

Triboulot-Trouy²,

Merlin³

et al. 1993

Ann. For. Sci.

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(fig 22) to take into account the discoloration of wood under solar-type light exposure at the molecular level. In this paper, this model was extended to European species of oak (Quercus robur and petraea) with high levels of colored extractable substances and for which the color characteristics are a quality criterion. In addition to the observed and analyzed yellowing in Abies grandis wood, a color lightening corresponding to a lowered absorption over the spectral range (500-600 nm) (figs 2, 6) has been observed. Lignin photodegradation is certainly in part responsible for this decoloration. It has also been shown that oak sapwood and heartwood undergo different kinds of photodecoloration (fig 3). For color photostabilization of oak wood under solar light, the results indicate that it is necessary to use UV absorbers to lower the yellowing due to UV light and antioxidants to inhibit color lightening due to reactions with oxygen.

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“…'~u t h o r to whom correspondence may be addressed. solution and in heterogeneous environments has been studied as a model for the P-cleavage processes in lignin (7)(8)(9)(10)(11)(12).…”

Section: Introductionmentioning

confidence: 99%

Photochemistry of lignin model compounds on solid supports

Hurrell¹,

Johnston²,

Mathivanan³

et al. 1993

Can. J. Chem.

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. Can. J. Chem. 71, 1340 (1993).The photochemistry of several substituted a-(aryloxy)acetoveratrones that are models for chromophores in lignin has been studied using a combination of laser flash photolysis and product studies in solution and on silica, Na-X zeolite, and cellulose. The lifetimes of the triplet ketones vary substantially with the electron-donating ability of the substituents in the a-aryloxy ring, with values ranging from 30 ns for the 4-methoxy derivative to 5.5 ps for the 4-cyano ketone in acetonitrile. The triplet ketones are considerably longer lived on a silica surface than in solution and do not decay with first-order kinetics; however, they are all shorter lived than triplet acetoveratrone under the same conditions, indicating that P-phenyl quenching and (or) P-cleavage dominate their decay. The same triplets show quite different kinetic behavior in Na-X or cellulose and there is no indication in these systems for the importance of either P-phenyl quenching or P-cleavage in determining the rates of triplet decay. Product studies for a-guaiacoxyacetoveratrone indicate that Pcleavage from the singlet excited state is responsible for product formation; in contrast to solution results, the phenacyl-phenoxyl radical pairs react exclusively by geminate recombination to give rearranged ketones resulting from ortho and para ring coupling of the two radicals. Product formation is very inefficient for this ketone in cellulose, indicating either a low singlet reactivity or efficient geminate recombination of the initial radical pair to regenerate starting material. Utilisant une combinaison de photolyse Cclair au laser et une Ctude des produits en solution, sur de la silice, sur une zColite Na-X et sur de la cellulose, on a CtudiC la photochimie de plusieurs a-(aryloxy)acCtovCratrones qui sont des modkles pour les chromophores de la lignine. Les temps de vie dcs cCtones triplet varient beaucoup avec les capacitts des substituants du cycle aryloxy ?i donner des Clectrons; les valeurs varient de 30 ns pour le dCrivC 4-mtthoxy 5 5,5 ps pour la 4-cyanocCtone dans I'acCtonitrile. Les cCtones triplet ont des temps de vie beaucoup plus ClevCs sur une surface de silice qu'en solution et leur dCgCnCrescence n'est pas du premier ordre; toutcfois, leurs temps de vie sont tous plus courts que celui du triplet de I'acCtovCratrone dans les mCmes conditions et ces rksultats indiquent que la relaxation P-phknyle et (ou) un clivage P dominent leur dCgCnCrescence. Les mCmes triplets prtsentent un comporternent cinCtique trks diffCrent avec Na-X ou la cellulose et il ne semble pas que, dans ces systi-mes, la relaxation P-phCnyle ou un clivage P joue un r6le important dans la determination de la vitesse de dCgCnCrescence de I'Ctat triplet. Des etudes de produit pour l'a-guai'acoxyacttovCratrone indiquent que le clivage P B partir de 1'Ctat singulet excitC est responsable pour la formation des produits; par opposition aux rksultats obtenus en solution, Ics paires de radicaux phenacyle-phCnoxyle rkagissent exclusivement p...

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Discoloration of α-Carbonyl-Free Lignin Model Compounds Under UV Light Exposure

Cited by 54 publications

References 26 publications

The photochemistry of 3,3′,4,4′-tetramethoxy-and 4-hydroxy-3,3′,4′-trimethoxystilbene — models for stilbene chromophores in peroxide-bleached, high-yield wood pulps

The photochemistry of 3,3′,4,4′-tetramethoxy-and 4-hydroxy-3,3′,4′-trimethoxystilbene — models for stilbene chromophores in peroxide-bleached, high-yield wood pulps

Modification de couleur du bois de chênes européens exposés à la lumière solaire

Photochemistry of lignin model compounds on solid supports

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