Bjorkman lignin

The second way consists of hot-water extraction of finely divided wood powder, previously extracted with aqueous dioxane for removing milled wood lignin. The resultant LCC-WE is obtained in 9.3-10.0% yield and does not differ from Bjorkman LCC in relation to chemical composition and molecular weight (11) (see Table I). This fact is very significant in demonstrating that LCC s containing up to 18% lignin are able to be extracted with hot water alone from wood powder. 

Hydrolysis of lignin in acidic and basic media has received attention due to the rather few and simple degradation products obtained. Acid-catalyzed hydrolysis reactions applied to isolated lignin have been studied by a number of workers. Lundquist (1), for example, subjected Bjorkman lignin to acidolysis and obtained significant yields of monomeric products. A review of the work prior to 1971 has been made by Wallis (2). 

Our constitutional scheme is based on different kinds of information. The first type of information comes from an analytical study of milled spruce wood lignin prepared according to Bjorkman (3). The analytical data considered comprise the elemental composition of lignin, its content of methoxyl groups and other ether bonds, the types and amount of its different hydroxyl groups, carbonyl, and lactone groups, and the kind and number of its biphenylyl linkages and other bonds in which the benzene nucleus is involved. The work that led to data of this kind has been carried out in various laboratories and has been described previously (9,11). 

Phenylcoumarone (VIII) has a characteristic ultraviolet and ioniza-tion-Ae spectrum, which enabled us to detect dimeric structures of this type in reaction mixtures obtained when Bjorkman spruce lignin was subjected to acidolysis for 20 hours. From the spectrophotometric estimation of the amount of the phenylcoumarone systems formed, we concluded that from a total of 100 phenylpropane units of Bjorkman lignin, about 20 are involved in phenylcoumaran systems (I) in other words, about every 10th phenylpropane unit is linked to one of its neighbors by the cyclic benzyl aryl ether linkage characteristic of I. 

The crude Bjorkman lignin acidolysis mixture contained both polymeric material and a number of more or less low molecular, chromato-graphically visible products in addition to ketol (XII) and was considered to be a potential source not only of further monomeric but also of dimeric and oligomeric degradation products. The polymeric material was readily removed by filtering the crude mixture of reaction products through a short silica gel column (solvent, dioxane-benzene 1 3). 

If a reaction mixture obtained after 4 hours acidolysis of Bjorkman lignin (spruce), after neutralization and removal of the polymeric material, were filtered through a Sephadex G 25 column, the elution curve (Figure 5) exhibited three peaks (26). The effluent fractions corresponding to peaks A and B were subjected to further fractionation by chromatography on silica gel columns. We found that fraction A contained only monomeric products while fraction B was a mixture of dimeric products (Figures 6 and 7). 

Finally, coniferaldehyde (XXI) was found 26) in fraction A in a quantity of about 0.5% of the lignin. The major portion of XXI probably originates from coniferaldehyde end groups linked to the lignin molecule by hydrolyzable ether bonds—i.e., a- and 0-aryl ether bonds. In agreement with this view, we found that borohydride-reduced Bjorkman lignin, when subjected to acidolysis, gave only traces of coniferaldehyde. 

The fraction of the Sephadex eluate, which corresponded to peak B (Figure 5), contained 5% of the weight of the Bjorkman lignin used in the acidolysis experiment. We expected it to contain dimeric acidolysis products. So far, five pure compounds (XXII-XXVI) have been obtained from fraction B. 

The color of kraft lignin as compared with the untreated Bjorkman milled wood lignin (spruce) is demonstrated by the curves for the Kubelka-Munk reflectance function F (R ) vs. the wavelength (Figure 1). The shoulder at around 500 mis particularly interesting since it is in the visible region. Sodium borohydride reduction of kraft lignin causes a certain... 

Softwood kraft lignin, 2) NaBH -reduced softwood kraft ligniny (3) Bjorkman spruce milled wood lignin... 

The ionization — Ae curve for untreated Bjorkman spruce milled wood lignin has a maximum at 357 m/z (Figure 5) which is attributed to phenolic a-carbonyl structures (31). Kraft-cooked Bjorkman lignin, however, has... 

Kraft-cooked Bjorkman spruce milled wood lignin, (2) Bjorkman spruce milled wood lignin. Solvents methylcellosolve-ethanol, 1 4 and IN NaOH in methylcello-solve-ethanol-water, 2 3 5. Curves recorded within 2 minutes after mixing the solutions. 

The p,0 -dihydroxystilbene III does not give any quinone on oxidation with H202/Cu+2, but the stilbene is destroyed. Neither do simple catechols give any significant color under the oxidation conditions used. Recently (75, 28) structures of type XI, or precursors of dienone type, have been demonstrated in Bjorkman lignin. Kraft cooking of XI presumably... 

The native Bjorkman milled wood lignin has a very slight yellow color and a low absorption in the visible part of the spectrum (Figure 2). If quinonemethides are present in the native lignin, as suggested by Harkin (20), the amount of such structures must be exceedingly small. 

Two lignin preparations were used in these experiments, milled wood spruce lignin (M.W.L.) prepared according to Bjorkman (< ), and a kraft pine lignin fraction. Both preparations were characterized earlier (M.W.L., (/, 8) kraft lignin (26)). Some pertinent data are given in Table I. 

Besides cellulolytic enzyme lignin, the so-called Bjorkman lignin, alternatively referred to as "milled wood lignin" (MWL) is the best preparation known so far, and it has been widely used for structural studies. When wood meal is ground in a ball mill either dry or in the presence of nonswelling solvents, e.g., toluene, the cell structure of the wood is destroyed and a portion of lignin (usually not more than 50%) can be obtained from the suspension by extraction with a dioxane-water mixture. MWL preparations always contain some carbohydrate material. 

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