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  • 1
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    Formation of Chloro-Organics During Chlorine Bleaching of Softwood Kraft Pulp. Part 2. Chlorination of Pine Kraft Lignin Fractions (1996)
    De Gruyter
    Details
    Publication Date: 1996-01-01
    Print ISSN: 0018-3830
    Electronic ISSN: 1437-434X
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by De Gruyter
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  • 2
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    Oxidative Ammonolysis of Technical Lignins. Part 3. Effect of Temperature on the Reaction Rate (2002)
    De Gruyter
    Details
    Publication Date: 2002-06-27
    Description: Summary The effect of the reaction temperature on the kinetics and the reaction mechanism of oxidative ammonolysis of Repap organosolv lignin have been studied. The reaction was conducted in 0.8 M Nh4oh solution under oxygen pressure of 12 bar and at three different temperatures, 70 °C, 100 °C and 130 °C. The resulting N-modified lignins were analyzed by elemental and methoxyl group. About 20–25% of maximum nitrogen content is incorporated into the lignin very fast, in 1–2 min of the reaction. The reaction kinetics then follows a pseudo-first order reaction law and consists of two phases. The activation energies for nitrogen incorporation and lignin solubilization are rather low, in the range of 33–34 kJ/mol. Linear correlation between nitrogen incorporated into the lignin and molecular oxygen uptake, oxygen incorporation, CO2 formation, O-demethylation and total carbon loss was analyzed at the different reaction temperatures. On the basis of kinetic data obtained so far, we have postulated that the reaction temperature affects the reaction rate, but not the reaction pathways. The reaction temperature also affects the ratios between different reaction pathways, though the effect is not very strong. The results obtained are discussed in the terms of competitive reactions of lignin oxidation followed by nitrogen incorporation and lignin deactivation involving nitrogen
    Print ISSN: 0018-3830
    Electronic ISSN: 1437-434X
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by De Gruyter
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  • 3
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    Confirmation of the Presence of Formaldehyde and N-(Methylene)morpholinium Cations as Reactive Species in the Cellulose/NMMO/Water System by Trapping Reactions (2000)
    De Gruyter
    Details
    Publication Date: 2000-01-28
    Description: Summary The presence of formaldehyde (4) in solutions of cellulose in N-methylmorpholine-N-oxide (NMMO, 1) has been shown by trapping formaldehyde as dimedone adduct 8 in a two-phase system. o-Dichlorobenzene was used as an inert solvent to extract the trapping product as soon as it had formed. Morpholine is a degradation product of NMMO and is always present in systems containing NMMO. Formaldehyde can react with morpholine to form an intermediate carbenium-iminium ion, N-(methylene) morpholinium (6). The occurrence of 6 in the system cellulose/NMMO was demonstrated by trapping this intermediate in a Mannich type reaction with 2-acetonaphthone (9). Both formaldehyde and N-(methylene)morpholinium cations are highly reactive species readily undergoing further reactions with nucleophiles. These processes might contribute to the observed discoloration of the reaction mixture, and might also be responsible for the decomposition of NMMO that is inducible by carbenium-iminium ions.
    Print ISSN: 0018-3830
    Electronic ISSN: 1437-434X
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by De Gruyter
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  • 4
    Electronic Resource
    Electronic Resource
    Darstellung und Oxydation von Hydroxybenzylalkoholen (1972)
    Springer
    Monatshefte für Chemie 103 (1972), S. 1178-1193 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Eine Reihe von Hydroxybenzylalkoholen wurde durch Reaktion von Phenolen mit Formaldehyd bzw. durch NaBH4-Reduktion der entsprechenden Hydroxybenzaldehyde dargestellt. Die Oxydation mit K3Fe(CN)6 führte in den meisten Fällen unter Abspaltung von Hydroxymethylgruppen als Formaldehyd zu polymeren Kupplungsprodukten, im Falle von 2,6-disubstituierten p-Hydroxybenzylalkoholen zu linearen Polyphenylenäthern. p-Hydroxybenzylalkohole mit elektronenanziehenden Substituenten ergaben die entsprechenden p-Hydroxybenzaldehyde. Die Oxydation mit O2 inDMSO in Gegenwart von Cu(I)Cl führte im Falle der o-Derivate meist zu oligomeren Produkten, die p-Derivate hingegen ergaben neben Oligomeren und p-Chinonen zumeist die entsprechenden Benzaldehyde als Hauptprodukte.
    Notes: Abstract Several hydroxy benzyl alcohols were prepared by reaction of phenols with formaldehyde, or by reduction of the corresponding hydroxy benzaldehydes with NaBH4. Oxidation with K3Fe(CN)6 yielded mainly polymeric products by radicalic coupling and loss of hydroxymethyl groups as formaldehyde (in case of 2,6-disubstituted p-hydroxy benzyl alcohols linear poly-phenyleneoxides were obtained). p-Hydroxybenzyl alcohols with electran withdrawing substituents gave the corresponding benzaldehydes. Oxidation with O2 inDMSO in the presence of Cu(I)Cl afforded in the case of o-hydroxy derivatives mainly oligomeric products, whilst in the case of p-derivatives the corresponding benzaldehydes were obtained as main products besides some oligomeres and p-quinones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00905194
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  • 5
    Electronic Resource
    Electronic Resource
    Zur Oxydation von14C-markierten Phenolen (Ligninmodellen) in wäßrig-alkalischer Lösung mit Sauerstoff (1967)
    Springer
    Monatshefte für Chemie 98 (1967), S. 891-904 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract o-Methoxyphenols withp-side chains labelled with14C at the α-C-atoms were synthesized and mildly oxygenated in dilute aqueous NaOH (0.2n, 1–2 mole equivalents NaOH) at 70° C. Derivatives with α-C-atoms in different states of oxidation exhibit different reaction patterns. In contrast top-alkyl-substitutedo-methoxyphenols which dimerize too,o′-dihydroxybiphenyls, eliminations of side chains according to theDakin reaction could be observed in the case of α-carbonyl, and α-carbinol derivatives, respectively. The carbon dioxide formed in the course of oxidation of models labelled with14C in α-position proved to be inactive and does definitely not originate from α-C-atoms. Possible reaction mechanisms are discussed, and to the importance of these particular elimination reactions in lignin chemistry is referred to.
    Notes: Zusammenfassung o-Methoxyphenole mit para-ständigen Seitenketten (an den α-C-Atomen mit14C markiert) wurden dargestellt und einer milden Sauerstoffoxydation in verd. wäßr. NaOH (0,2n, 1–2 Moläquivalente NaOH) bei 70° unterworfen. Das Reaktionsverhalten hängt dabei von der Struktur (Oxydationsstufe) am α-C-Atom der Seitenkette ab. Im Gegensatz zup-alkylsubstituierteno-Methoxyphenolen, die zuo,o′-Dihydroxydiphenylverbindungen dimerisiert werden, konnten bei den α-Carbonyl- bzw. α-Carbinolderivaten Seitenketteneliminierungen im Sinne derDakin-Reaktion beobachtet werden. Das bei diesen Oxydationen abgespaltene CO2 erwies sich bei den Versuchen mit α-14C-markierten Modellen als inaktiv und entsteht daher mit Sicherheit nicht aus den α-C-Atomen. Mögliche Reaktionsmechanismen werden diskutiert; auf die Bedeutung dieser Eliminierungsreaktionen für die Ligninchemie wird hingewiesen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00901392
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  • 6
    Electronic Resource
    Electronic Resource
    Der β-Guajacyläther des Guajacylglycerins, seine Umwandlung in Coniferylaldehyd und verschiedene andere Arylpropanderivate (1959)
    Springer
    Monatshefte für Chemie 90 (1959), S. 771-782 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Zusammenfassung Eine Variante derAdlerschen Synthese für den β-Guajacyläther des Guajacylglycerins (VI) wird beschrieben. Die Spaltung mit Na-fl. NH3 nachSchorygina lieferte neben anderen phenolischen Substanzen etwas Guajacyl-propanol-(2) (X) und Dihydroeugenol (XI), ähnlich dem Fichtenholz. Bei der hydrolytischen Spaltung gibt VI, neben Guajacylaceton (XVIII) und Vanillin Coniferylaldehyd (XIV). Da man aus Holz durch ähnliche hydrolytische Abbaumethoden (Goldschmidt) mehr Coniferylaldehyd erhält, als vor der Hydrolyse nachweisbar war, scheint die Konfiguration (VI) nicht nur der Progenitor derHibbertschen Ketone (Adler), sondern auch eine Maskierung des Coniferylaldehydsystems im Lignin darzustellen, wie Verf. es am Guajacylglycerin (XII) bereits 1946 formuliert hatte. Dies zeigen besonders die Sulfitierung und alkalische Hydrolyse. Der Sulfitaufschluß von VI lieferte Sulfosäuren, die bei anaerober alkalischer Hydrolyse hohe Ausbeuten an Vanillin und Acetaldehyd ergaben, welche formale Spaltprodukte des Coniferylaldehyd XIV bzw. reale der Sulfosäure XV darstellen. VI gibt bei alkalischer Hydrolyse allein (also ohne vorhergehenden H-Ioneeinfluß bzw. Sulfitierung) keinen Acetaldehyd und kein Vanillin. Erst durch Sulfitierung wird das spaltbare System gebildet. Der Guajacylglycerin-baustein (verknüpft vorwiegend in β-Stellung durch Ätherbindung), der nachAdler zu etwa 30% im Lignin vorhanden ist und auch die Hauptmenge der Zwischenprodukte der biochemischen Dehydrierung des Coniferylalkohols (Freudenberg) darstellt, dürfte somit für sehr viele Reaktionen verantwortlich sein, die zu einfacheren Bruchstücken des Lignins führen. So lassen sich zwanglos die wichtigsten Abbauprodukte, z. B. Vanillin (Oxydation), Cyclohexylpropanole (Hydrogenolyse),Hibbertsche Körper (Äthanolyse, Acidolyse), Vanillin+ Acetaldehyd (Sulfitierung und alkalische Hydrolyse), Acetovanillon+ Formaldehyd (Hydrolyse), Guajacylpropanole (Na+ fl. NH3),Hibbertsche Körper und Coniferylaldehyd (saure wäßrige Hydrolyse) usw., ableiten. Aber auch für einen großen Teil des reaktiven Verhaltens des Lignins, z. B. bei der Sulfitierung (Lindgreen, Adler) und Methylierung (Adler, Gierer) sowie Sulfidierung (Lindgreen, Gierer), ist vorwiegend die Benzylalkoholgruppe des Guajacylglycerinsystems in freier oder eventuell verätherter Form verantwortlich.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00905664
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  • 7
    Electronic Resource
    Electronic Resource
    Topochemistry of delignification in Douglas-fir wood with soda, soda-anthraquinone and karft pulping as determined by SEM-EDXA (1982)
    Springer
    Wood science and technology 16 (1982), S. 139-153 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Delignification studies on 0.5 μm sections of Douglas-fir earlywood tracheids pulped by soda, soda-anthraquinone (soda/AQ) and kraft pulping processes were performed by determining bromine concentrations in various morphological regions with SEM-EDXA technique. Soda/AQ pulping was much more selective in removing lignin from the middle lamella regions than either soda or kraft pulping. However, up to 50% delignification, more lignin was removed from the secondary wall by soda or kraft, compared to soda/AQ pulping. The kinetics of lignin removal in the various morphological regions were established. Addition of AQ and sodium sulfide resulted in an earlier transition from a slow initial to a rapid bulk delignification, particularly in the middle lamella, and in an enhanced bulk delignification in the secondary wall. Anthraquinone was also found to promote residual delignification in the secondary wall, where sodium sulfide was not effective. The opposite was observed for the bulk delignification in the middle lamella, where only sodium sulfide addition improved the rate significantly. The great differences observed in the bulk delignification rates between middle lamella and secondary wall in soda pulping as well as their response to additives suggest structural differences between middle lamella and secondary wall lignins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00351099
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  • 8
    Electronic Resource
    Electronic Resource
    Model studies on reactions occurring in oxidations of lignin with molecular oxygen in Alkaline Media (1974)
    Springer
    Wood science and technology 8 (1974), S. 35-49 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Basic reactions governing the degradation of lignin in oxidation with molecular oxygen are discussed emphasizing the radical (homolytic) or one-electron transfer-oxidations in the initial phase. The critical oxidation potentials (COP) according to Fieser were found to represent a useful measure for the ease of electron release from lignin-related phenolic models. At low alkalinity rough correlations were observed between the measured COPs and the initial oxygenation rates. The results obtained from quantum mechanical calculations of critical oxidation potentials are briefly discussed. The importance of phenoxy radicals and the hypothetical cyclohexadienone hydroperoxides as intermediates is outlined in view of such degradation reactions as oxidative side-chain eliminations, demethoxylations, and splitting of aromatic rings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350641
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