US3071570A - Oxidative demethylation of lignin - Google Patents

Description

3,971,570 Patented Jan. 1, 1983 This invention relates to alkali lignin derivatives possessing increased aromatic reactivity and relates particularly to a process for treating lignin recovered from spent alkaline cooking liquors whereby increased aromatic reactivity is imparted thereto.

Lignin, as it occurs in wood, has been extensively investigated in recent years to determine its botanical origin and chemical structure. Lignin has usually been considered to be composed of structural elements such as phenyl and furan groups with an assortment of hydroxyl and methoxyl groups, but, according to modern views on the structure of lignin as it occurs in coniferous woods, this natural product is built up of guaiacyl propane units which are linked together with different types of bonds, in some 2O propane unit and which are Typical compounds which incorporate the guaiacylbelieved to be proper models for building stones of softwood lignins, with probable types of linkages illustrated, are:

l O Qll ofi a? 3 'sa H4 k C F o Ju gi tsgaugasg u, E 552F1 HG CH 5 1 H-c o 3 case "a l Seli W i i 06H i L" new I R Hydrogen atom or carbon -a oom of another guaiacyl propane chain.

the carbon atoms of the propyl It is widely acknowledged, however, that sulfate cooking, in particular, substantially increases the proportion, in softwood lignin, of guaiacyl propane building units having a free phenolic group in the No. 4 position as compared to natural lignin; breakage of aryl-alkyl-ether bonds by thioalcohol groups in alkaline solution is thought to be responsible. Since the structure of lignin, particularly the altered lignin recovered after alkaline digestion of wood, is not known with precision, the reactions which occur cannot be stated with exactness, but it is believed that certain reactions take place, as deduced from studies of model compounds, which are reasonably consonant with those set forth hereinafter.

As is well known, the presence of a free phenolic hydroxyl increases the aromatic reactivity of both of the adjacent (ortho) positions and of the opposite (para) position on an aromatic nucleus. Since the para position of a guaiacyl propane unit (position No. l) is usually occupied by the propyl chain and one of the ortho positions (position No. 3) is filled with a methoxyl group, the only remaining position possessing potential aromatic reactivity is the other ortho position, hereinafter termed the No. 5 position, which may or may not be filled by a linkage with a propyl carbon of another guaiacyl propane unit or even by a diphenyl type of bond. Disregarding the relatively small proportions of aldehydic, ketonic, and alcoholic groups on the propane side chains, which are non-aromatic in their reaction conditions, the principal determinative factor in the reactivity of natural lignin is the number of these No. 5 positions-on the guaiacylic nuclei which are unoccupied. Similar considerations are valid for hardwood lignin, except that syringyl groups occur in addition to guaiacyl groups.

If the compounds incorporating guaiacyl propane units, as described hereinbefore, represent those which have persisted in softwood lignin through alkaline digestion and recovery processes, it is clear that both free and condensed S-positions may exist on the aromatic nuclei of the phenolic guaiacyl propane units. Replacement of methoxyl groups (in position No. 3) with hydroxyl groups, moreover, should add two aromatically reactive positions (one ortho and one para, positions 2 and 6) to each aromatic ring having a condensed S-position, thereby multiplying significantly the total aromatic reactivity of the recovered lignin and enhancing its usefulness in many applications.

For example, in the case of guaiacyl-propane units having a free 5-position, there would be two new reactive positions created ortho and para to the new phenolic OH group, as in the trifunctional demethylation product on the right below, where the reactive positions are marked with an asterisk:

ocH H For guaiacyl-propane units containing condensed and thereby blocked 5-positions, the demethylation product becomes bifunctional:

Chemical building units of trifunctional or bifunctional nature, containing guaiacyl propane units converted into pyrocatechol structures, should show considerably increased reactivity towards formaldehyde and greater cross-linking potential in many useful reactions.

Among studies of model compounds of the type believed to occur in lignin have been several studies on the aromatic substituents of guaicol and guaicol-based deriva- A tives. For instance, Adler desc bed in Acta Chemica Scandanavia 9 (1955), No. 2, 319-334, an analytical method for determination of guaiacyl groups which depended upon sodium metaperiodate liberating methanol quantitively by a rapid oxidative demethylation process from guaiacol and similar compounds but not from compounds of the veratrol type in which the phenolic group in the No. 4 position had been etherified, forming an additional methoxyl group or a linkage with a carbon of an adjacent compound.

In these determinations the periodate solution was allowed to react at 4 C. upon the model compounds or the protolignins for as long as hours. To obtain substantially complete demethylation, a reaction time of 16 to 48 hours was necessary. The reactions were stopped and the compounds were precipitated by addition of a solution of lead nitrate.

Experiments with natural lignins, reported in Svensk Papperstidning, 61 (1958), 18B, 641-647, showed that these materials also produced methanol upon treatment with sodium metaperiodate, leaving highly polymerized, unreactive lignin residues which were generally insoluble in the usual lignin solvents. In contrast to the rapid production of methanol by guaiacol-type compounds, however, these lignins liberated methanol partially in a rapid phase and partially in a slow phase.

Somewhat similar to the oxidative demethylation process forming a portion of this invention is the reductive dimethylation process with hydriodic acid, as given by Moore et al., in the Canadian Journal of Research, 15B (1957), page 532, in which high reaction temperatures, a high concentration of H1, an excess of HI, and a lengthy reaction time are required. Reductive demethylation, moreover, is not specific as is oxidative demethylation, for many methoxyl types, including both guaiacyl and veratryl, are attacked, and the reductively demethylated lignin product is polymerized and destructively degraded to a non-useful product.

One of the most widely-available sources of lignin is spent liquor in the sulfate and soda processes which is commonly concentrated and burned to recover heat values and inorganic cooking chemicals. This lignin may be recovered as a water-soluble alkali lignate or as a waterinsoluble alkali lignin of low ash content by processing the concentrated, spent cooking liquor according to the principles and methods of US. Patent No. 2,464,828. It must be borne in mind, however, that after undergoing the relatively drastic conditions occurring in the digestion of wood by the soda or sulfate processes, the natural lignin in either hardwoods or softwoods is changed to a degree that is unknown and as yet only cursorily investigated.

In studies of alkali lignin recovered from spent sulfate liquor after digestion of coniferous woods, it has been determined that, of the guaiacyl propane units which are believed to comprise the lignin, nearly two-thirds are phenolic in type, having free phenolic OH groups in position No. 4. Of these phenolic guaiacyl propane building units, about one-third possess a position ortho to the phenolic hydroxy (i.e., the No. 5 position on the phenyl ring) which is free and thus accessible to the introduction of methylol groups, for instance, by aromatic reactions. Using very approximate averages, out of every guaiacyl propane building units, therefore, about 22 are phenolic groups and possess free No. 5 positions with resultant capacity to become tri-functional after demethylation, about 42 are phenolic groups and possess blocked No. 5 positions with resultant capacity to become bi-functional after demethylation, and about 36 are non-phenolic groups having etherified No. 4 positions which are apparently incapable of aromatic reactivity or of attaining increased aromatic; reactivity by the methods of this invention.

Chemical determination of hydroxyl groups was made. according to the method given in Chemische Berichte, 88, 617 (1955) in an article by K. Freudenberg and H,

j H+ was,

Alkali lignin, recovered according to US. Patent No. 2,464,828, has been utilized as an extender of phenolformaldehyde resins, urea-formaldehyde resins, epoxy resins, isocyanate foams, and styrene-butadiene elastomers. A method of increasing the aromatic reactivity of this lignin has wide usefulness in many practical applications, involving such fields of use as casting sands, paper and fiberglass laminates, wood glues, hardboard, molded articles, insulation foams leather tanning, rubber tires, and rubber heels.

The object of this invention is to increase the reactivity of alkali lignin and more specifically to increase the reactivity of alkali lignin toward aldehydes.

A chemically sound way to attain this objective is to increase the aromatic reactivity of the lignin whereby additional substitution reactions on the guaiacol nucleus may be used for accomplishing such reactions as chloromethylation, the Mannich reaction, phenol-formaldehyde resin condensations, urea-furfural resin condensations, bromination, and nitration, for example. Conversion of guaiacyl structures in softwood-derived alkali lignin into pyrocatechol structures and of syringyl structures in hardwood-derived alkali lignin into pyrogallol structures by replacement of methoxyl groups with hydroxyl groups is a practical way of attaining increased aromatic reactivity.

It has now surprisingly been found that the periodate reaction can be utilized to increse the aromatic reactivity of alkali lignin by carefully controlling the extent of oxidative demethylation and rapidly reducing the product obtained thereby.

Increased aromatic reactivity in alkali lignin is attained according to this invention by dissolving the lignin in a solvent that is inert to the oxidative demethylating agent, adding and rapidly mixing the oxidative demethylating agent, and quickly stopping the reaction with a reductant, the degree of reaction being controlled by removing heat from the reaction materials before mixing or during the reaction and by limiting the duration of the reaction.

It is believed that this invention is effective because the oxidative demethylation reaction of sodium metaperiodate upon alkali lignin does not convert methoxyl groups to hydroxyl groups but instead forms quinone groups which are veryreactive and tend to dimerize by diene-addition and form a lignin product of lowered reactivity and insolubility:

example, is usable, but ethanolarnine is not.

Therefore, by adding an excess of a reductant such as sulfur dioxide to remove any excess of the demethylating agent and to convert the demethylated lignin into a somewhat less reactive form, polymerization by diene-addition can be avoided and a stable lignin product of increased aromatic reactivity can be obtained.

The reaction which seems to occur in the oxidative demethylation procedure may be expressed, for a typical guaiacol-propane unit, employing sulfur dioxide as the reductant source, as:

Other oxidants are able to oxidatively demethylate lignin. For instance, the lithium, sodium and potassium salts of bismuthate, persulfate, tungstenate, chlorite, hypochlorite, hypobromite, and hypoiodide anions and chlorine dioxide with chlorine are effective agents. Hydrogen peroxide and ozone are also potentially useful oxidative demethylants. For reduction, a choice might be made among sulfur dioxide and lithium, sodium, and potassium thiosulfate.

The oxidative demethylation reaction may be conducted in any lignin solvent which is itself compatible with periodic acid, for the periodate ion, as liberated by the acid or any of its salts, is actually the active agent in this reaction. The reaction, moreover, is catalyzed by protons, and for this reason a-lkalis are not usable. Phenol, for

Suitable solvents, for example, are acetic and formic acids and their chlorinated derivatives, 1,4-dioxane, dimethyl sulfoxide, ethylene chlorohydrin, thymol, and the cresols. If an organic solvent is selected, however, it is necessary to add an aqueous acid for the oxidative demethylation step; it is also desirable to have at least two moles of water for each S0 mole present during the reduction step as a supply source for hydrogen ions.

Experimental work was performed on purified alkali lignin isolated from spent sulfate liquor after digestion of southern pines in a typical kraft papermakiug process. The experimental results, as to yield and methoxyl contents of the oxidized and 'SO -reduced products, are given in Table 1. The experimental procedure in general which was used is illustrated hereinafter by Example No. 8 in which the reaction was conducted at ice-water temperatures.

EXAMPLES 1-7 In Examples 1, 2, and 3, 1.85 ocH -rnilliequivalents of alkali-pine lignin (0.4 g.) were dissolved in 2.5 ml. of warm acetic acid; after cooling to 20 C., 30 m1. of a 0.14

worked up as described in Example AcOH, and 250 ml. of 0.14

molar NaIO solution were used (reaction time 20 min.). After reduction with S fractional dilution with water yielded a first precipitate (4a) in 58% yield, and a further one (4b) in 9% yield. Similar yields were obtained in Examples 1-3 for the initial precipitation only. Example .5 was run in a non-solvent acid medium, 0.14 molar H SO at 20 C. for 30 minutes, tent was merely reduced to 13.72%.

Examples 6 and 7 were made with sodium persulfate, Na S O as the sole or principal oxidative agent, but the resulting reduction in methoxyl content was inconsequential. It was concluded that lignin would not be demethylated to an effective degree if reacted upon when in slurry form.

Table 1 but the methoxyl con-.

and SO -reduction must have been phenolic hydroxyl groups, available for remethylation by diazomethane, and that only a minor amount of the intermediate o-quinoid groups could have undergone dimerization.

The same secondary periodate precipitate in 12% yield (817) was reduced with sodium borohydride, NaBH Evaluation of the results by light transmission measurements indicated that small amounts of phenolic a-ketone groups had been formed by the periodate reaction. Possibly 0.05 a-hydroxypropioguiacone units or, more probably, 0.02-0.03 vanillin structures had been created per orignal methoxyl unit.

The solubility of the demethylated products of Examples 1-8 was distinctly lower in the common lignin sol- OXIDATIVE DEMETHYLATION, USING $02 GAS AS THE REDUCTANT MATERIAL, OF ALKALI LIGNIN (OCHs content: 14.16%)

Moles Product OCT-I3 Ex Demethylating agent NaIOr/ Liquid solvent Temp, Time, yield, content, No. moles C. min. percent percent OGHz,

2. 3 75% acetic acid 10 57 7. 52 2. 3 do 20 65 6. 99 2. 3 20 120 63 7. 90 2. a 20 20 ss e. 13 9 2. 20 30 90 13. 72 20 30 95 14. 05 d0 20 30 92 14. 19 7.3% acetic acid 0 2 a 68 7. 66 b 12 6. 84 1.0 80% acetic acid 02 2 92 8. 08 5 60% AcOH 20 10 72 6. 58

* First precipitate. b Second precipitate.

EXAMPLE 8 Alkali pine lignin, insoluble in water, (4.4 g.) Was'dissolved in warm acetic acid (90%, 250 ml), the solution cooled to 2-3 C., and 250 ml. of an ice-cooled solution of sodium metaperiodate (0.14 moles of NaIO dissolved in 400 ml. of water and the solution made up to 1000 ml. with acetic acid) were added. After 3 minutes the reaction was stopped by introducing a vigorous stream of S0 gas, while the reaction mixture was cooled with icewater. After about 3 minutes, when the dark red color of the reaction mixture, indicative of the formation of o-quinones, had turned into a lighter shade, 500 ml. of water were added. The precipitate formed was centrifuged ofi, washed three times with small amounts of water, and dried in vacuo over P 0 and NaOH. Yield was 3.0 g., i.e., 68% (fraction 8a). While the washing procedure caused part of the material to peptize, another part remained dissolved in the mother liquor which still contained about acetic acid. The wash waters and the mother liquor were combined and diluted with water to 2 liters; the precipitate obtained was collected by centrifuging, washed twice with a small amount of Water, and dried as above. Yield was 0.5 g., i.e., 12% (fraction 8b).

As shown by the methoxyl contents of the principal reaction products in Table 1, such as (8a), about of the original amount of OCH had been removed. It was thought possible that the residual fraction of the reaction products (30-35% of the alkali lignin used), which were highly soluble in the dilute aqueous acetic acid mother liquors and therefore were not recovered, had considerably lower methoxyl contents, but the methoxyl content of the secondarily-recovered product (8b) was reduced only a 6.84%, i.e., 48% of the original methoxyl as compared to 54% for (8a).

The precipitate in 12% yield (8b), from the second dilution with water, had lost 54% of its original 001-1 groups. After methylation with diazomethane, this material increased in methoxyl content from 6.84% OCH to 21.52%. Alkali lignin was similarly methylated. After comparison of the results, it was concluded that the majority of the groups formed on oxidative demethylation vents than that of untreated water-insoluble alkali lignin. This loss in solubility seemed to indicate that some polymerization of the primarily-formed o-quinoid elements had taken place before the reduction with S0 was carried out. as discussed hereinbefore.

EXAMPLE 9 This reaction was completely successful in obtaining an unpolymerized product, apparently because of using the molar ration of 1:1 for OCH :IO 8.8 grams of alkali lignin, containing 40 Inilliequivalents of OCH groups, were dissolved in 500 ml. of acetic acid, cooled to a temperature between 0 C. and 2 C., and mixed rapidly with 285 ml. of 0.14 molar NaIO solution, containing 40 milimoles of iodate equivalent. After exactly 2.0 minutes reaction in which the solution had become violet colored, S0 gas was introduced rapidly, turning the solution from violet to brown.

After reduction four liters of water were added to the solution, precipitating the reduced demethylated lignin. The precipitate was centrifuged and washed with water three or four times. For the final washing, a single drop of perchloric acid was added to the wash water to overcome peptization properties of the lignin and promote dewatering of the lignin. The centrifuged, washed lignin was then'dried at 60 C. in air.

The yield was 8.1 grams or 92% of the original material. The product was added to dioxane; 5% did not dissolve and was removed by filtering. The dioxane solution was added to ten times its volume of ether, and the precipitate was centrifuged, washed twice with ether, and once with petroleum ether, and dried. The reaction prod not, after precipitation with water and recovering, was obtained in 92% yield, was completely soluble in dioxane, and contained 8.65% OCH and 0.4% ash or 8.68% OCH on an ash-free basis.

EXAMPLE 10 Repeating the successful molar ratio of Example 9, this experiment used a 1:1 ratio of IO. ':OCH The reaction temperature was raised to 20 C., and the reaction time was increased to 10 minutes. The resulting yield, however, was only 72%, as given in Table 2, compared to 92% for Example 9, but the methoxyl content was decreased to 6.58%.

In the analytical termination,

procedure of phenolic hydroxyl dedemethylation of alkali lignin did proceed i 3 merit. It could be stated that 80% of the 2,6-positions of the pyrocatechol nuclei had undergone substitution by CH OH groups. Another way of expressing the results is that each newly formed phenolic hydroxyl group permitted almost two new methylol groups .to enter the defurther than in these examples; typically, 65% of the methylated lignin and that at least 80% of the 2,6-positotal amount of OCH was recovered as (ll-1 9E. The tions of the nuclei of kraft lignin are free, as the followdiscrepancy between the preparative experiments above ing general equation illustrates:

I r g he IOH CH o 26: AC; 3' I -l- & -"-il R OH CQ l R t Ci-l (1543 on and the typical analytical results is probably due to the fact wherein R represents the substantially unaltered alkyl side that, as observed with other lignin preparations, part of chain of the original guaiacyl propane structure and R the guaiacyl residues are demethylated comparatively stands for a bond between the carbon atom of the phenyl slowly and had not reacted during the short time intervals ring in the equation and the carbon atom of another phenyl used in these examples as compared to the long time of group or of another propyl side chain. reaction (2-3 days) applied in the analytical procedure. Because alkali lignin, properly demethylated and re- EXAMPLES 11 14 duced, had the same reactivity with chlorocresol as the original alkali lignin, and further, because the aromatic ljour afldltlqnal exampigs are hsterd i b In @3911 nuclei of untreated alkali lignin reacted with only 0.31 lhese eper lmemsi an amount OI alkah hgmn contam' moles of formaldeyhde, whereas the demethylated lignin F 5 mllhequlvalents of H grollps w used reacted with 0.95 moles of formaldehyde, calculated on the slum persulfate as an alternative ox1dative' demethylat ng same basis, the increase in reactivity toward f0rma1de 5 hgher rfiacfiofl temperatufiis and longer hydetreatment could have been caused only by the higher tlmfas were, exglored m expeilments' After the aromatic reactivity of the demethylated product. It was damn period m each the mlxture was f f with concluded that the reactivity of kraft lignin in phenolgflsfious S02 and i diluted wlth,water' The hgnin formaldehyde condensation could be increased significipitate was centrifuged, washed with water, and dried. camly by means of a carefully controlled demethylafion process. Table? The oxidative demethylation of alkali lignin in acetic gfiil i gg i gigggagg acid with sodium metaperiodate is a very rapid reaction. It is most suitably conducted in a continuous process, as Ill-Quid OCHS in a pipeline reactor, in which the reductant, such as sul- Ei Demethylating Solvent, Temp, Time not content, atur dioxide, may be added within seconds after iodate agent (mmols) 1323,? o zli g percent addition, according to experimental determinations of optimum reaction time and optimum reaction tempera- Kflszos (3,2) 70 181mmv 80 11.20 ture. Oxifdantive derl liethylation is irlijcreaksiedl1 by larger 12-- IQSZOEQQ) Q 50 37 9.70 amountso t edemet ylative oxidant, ya ig. er reaction if M104 2O 20 76 1183 temperature, and by a longer reaction time. The use 14-- K2S20s(5) 80 20 40 77 13-58 of over two moles of sodium metaperiodate per mole 50 equivalent of methoxyl causes an excessive amount of The demethylated product of Example 9 was condensed secondary condensations to occur, giving undesirable with chlorocresol in presence of hydrochloric acid cataamounts of a polymerized, insoluble product and conlyst. The results indicated that 0.28 chlorocresol units per sequent loss of yield. OCH groups originally present in alkali lignin had been in a mildly-prepared lignin, such as Bjorkman lignin introduced into the oxidatively demethylated lignin of this 55 which is now considered to be very close to natural lignin invention, exactly the same as for the original alkali lignin, in a structural sense, every third guaiacyl propane buildindicating that the main structural features of the proing unit has a free phenolic OH group. The lignin of pane side chains responsible for this condensation had not either coniferous or deciduous woods when subjected to been altered by the oxidative demethylation. alkali cooking undergoes certain different structural The same demethylated product was then methylolated 0 changes; from the viewpoint of this invention the most with formaldehyde and the resultant material was further important consists of that part of the ether-phenolic linkreacted with chlorocresol, producing a product that had ages which are broken by cooking, producing alkali lignin 1.23 chlorocresol units per OCH group present in the which has free phenolic groups in about two-thirds of the original alkali lignin, indicating that 0.95 chlorocresol units building units. Because the method of this invention per original OCH had reacted with the methylol groups 5 works only with such building units having free phenolic introduced by formaldehyde after demethylation. Calhydroxyls, the economic advantages are obvious for alkali culations showed that the oxidative demethylation prolignin as compared to natural lignin. cedure had resulted in the introduction of 40 phenolic Afteroxidative demethylation of alkali lignin according hydroxyl groups, replacing a corresponding number of to the methods of this invention, the propyl side chains methoxyl groups out of each 100 OCH groups of alkali are unchanged, as demonstrated by the chlorocresol exlignin. After methylolation, but not directly, these new per-iment described hereinbefore and by other evidence; phenolic groups enabled 64 chlorocresol units to be linked furthermore, carbon-to-carbon bondings, between propyl to the nuclei, meaning that every newly-formed phenolic carbon atoms of two adjacent side chains, between a OH group had enabled 1.6 chlorocresol-reactive methylol propyl carbon and a carbon of a guaiacyl nucleus, or groups to be introduced after alkaline formaldehyde treatbetween the carbons of two guaiacyl nuclei, are not broken to a measurable extent. Even more significantly, for the 22% of the guaiacyl propane units having ether bonds at the No. 4 position, the ether bonds in which an oxygen atom links the carbon of a guaiaeyl nucleus to the carbon of a propyl side chain or to the carbon of another guaiacyl nucleus, are also not broken. In the oxidative demethylation reaction of this invention, only a certain type of ether linkage, termed a methoxyl group, in which oxygen joins the carbon of a guaiacyl nucleus to the carbon of a free methyl group, is attacked, provided that a phenolic hydroxyl group is in ortho position to the methoxyl group. The reaction of this invention, therefore, is specific.

Moreover, as demonstrated experimentally with Example No. 9 hereinbefore, the reaction is easily controllable and technically uncomplicated. A. continuous process which includes the continuous regeneration of the iodate ion to the periodate ion by electrolytic oxidation is economically sound and can produce the reactive lignin product of this invention at a cost rendering it attractive as a useful substituent in phenolic resins in the same manner as, and even more usefully than, the original alkali lignin.

When the product of this invention is treated with formaldehyde, a large number of reactive benzyl alcohol groups, i.e., methylol groups, are introduced into the guaiacyl nuclei than can be introduced into the guaiacyl nuclei of original or ordinary alkali lignin. These methylol groups, by their inherent nature, as demonstrated hereinbefore with chlorocresol, can be condensed with phenols, cresols, etc., and provide substitution sites for extending and reacting with phenolic materials to form thermoset-ting resins as is well known in the art.

Practical examples of lignin uses, and particularly of uses for a lignin of increased chemical reactivity, are, in the resin field: phenol-formaldehyde-lignins for molded products, as taught in No. 2,357,090 and No. 2,282,518; lignin-containing coating compositions, as taught in No. 1,899,526 and No. 2,242,601; phenol-formaldehyde-lignin shell-molding resins, as taught in No. 2,751,650; phenolformaldehyde-lignin resin adhesives for lignocellulose products such as plywood, as taught in No. 2,878,197; and phenol-formaldehyde-lignin resoles for impregnating paper in the manufacture of laminates, :as taught in No. 2,683,706 and No. 2,725,321. Other uses may be illustrated with the elastomer field by No. 2,608,537 for ligninrubber elastomers, No. 2,906,718 for lignin-rubber-polyisocyanate rubber, and No. 2,854,422 for lignin-diisocyanate elastomers.

We claim:

1. The method of oxidatively demethylating alkali lignin which comprises reacting said lignin with an oxidizing agent, selected from the group consisting of sodium and potassium salts of bismuthate, periodate, persulfate, tungstenate, chlorite, hypochloride, hypobromide, and hypoidodide anions, chlorine dioxide with chlorine, hydrogen peroxide, and ozone, to convert guaiacol structures into o-quinoid structures, and, before the occurrence of a significant degree of polymerization by diene addition of said quinoid structures, stopping the reaction with a reducing agent selected from the group consisting of sulfur dioxide, sulfurous acid, sodium thiosulfate, and potassium thiosulfate, to convert said o-quinoid structures into pyrocatechol structures.

2. The method of claim 1 wherein the lignin is dissolved in a solvent which contains pro-tons and is inert to the oxidizing agent.

3. The method of claim 1 wherein the reduction is conducted in a solvent which is a source of hydrogen.

4. The method of claim 1 wherein both oxidative demethylation and reduction are conducted in aqueous acetic acid.

5. The method of claim 1 wherein the oxidative demethylating reaction is carried out at temperatures lower than ambient.

6. The method of claim 4 wherein the reaction occurs for a time inversely proportioned to the temperature, a temperature of 0-4 C. corresponding to 2.0 minutes.

7. The method of increasing the aromatic reactivity of alkali lignin comprising the reacting of said lignin with up to 1.5 moles of sodium metaperiodate per mole of methoxyl groups in the lignin and subsequently adding sulfur dioxide, said lignin being dissolved in a solvent inert to sodium metaperiodate, containing protons, and capable of supplying hydrogen.

8. The method of claim 7 wherein the reaction is conducted at temperatures of 0-4 C.

9. The method of claim 7 wherein the reaction proceeds for up to 2.0 minutes.

10. The method of increasing the aromatic reactivity of alkali lignin by reacting said lignin, dissolved in warm acetic acid at a lignin concentration of 1 to 5% and cooled to 0 to 20 C., with sodium metaperiodate at 0 to 20 C. for 1 to 3 minutes, employing up to 1.0 moles of said periodate per 1.0 moles of methoxyl groups in the lignin, and reducing the reaction product with sulfur dioxide while cooling.

11. The method of preparing water'insoluble and substantially ether-insoluble derivatives of alkali lignin having increased aromatic reactivity, as characterized by capacity to add larger proportions of methylol group by reaction with formaldehyde as compared to the original alkali lignin, comprising oxidatively demethylating said lignin to convert guaiacol structures into o-quinoid structures and, before the occurrence of a significant degree of polymerization by diene addition of said quinoid structures, reducing said o-quinoid structures to pyrocatcchol structures.

12. The method of claim 11 wherein the alkali lignin is oxidatively demethyl-ated with an agent selected from the group consisting of the sodium and potassium salts of bismuthate, periodate, and tungstenate and wherein the o-quinoid structures are reduced to pyrocatechol structures with an agent selected from the group consisting of sulfur dioxide, sulfurous acid, sodium thiosulfate, and potassium thiosulfate.

13. The product produced by the method of claim 11.

References Cited in the file of this patent UNITED STATES PATENTS 2,669,592 MacGregor et a1 Feb. 16, 1954 FOREIGN PATENTS 1,213,766 France Apr. 4, 1960 899,655 Germany Dec. 14, 1953 1,013,285 Germany Aug. 8, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 3 071570 January 1 1963 Joseph Merton et a1,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Coll unn i1 lines 55 and 56 for "hypochloride, hypobromide, and hypoldodlde" read hypochlorite hypobromite, and hypoiodite Signed and sealed this 10th day of September 1963a (SEAL) Attest:

DAVID L. LADD Commissioner of Patents ERNEST W. SWIDER Attesting Officer

Claims (1)

1. THE METHOD OF OXIDATIVELY DEMETHYLATING ALKALI LIGNIN WHICH COMPRISES REACTING SAID LIGNIN WITH AN OXIDIZING AGENT, SELECTED FROM THE GROUP CONSISTING OF SODIUM AND POTASSIUM SALTS OF BISMUTHATE, PERIODATE, PERSULFATE, TUNGSTENATE, CHLORITE, HYPOCHLORIDE, HYPOBROMIDE, ANDD HYPOIDODIDE ANIONS CHLORINE DIOXIDE WITH CHLORINE, HYDROGEN PEROXIDE, AND OZONE, TO CONVERT GUAIACOL STRUCTURES INTO O-QUINOID STRUCTURES, AND, BEFORE THE OCCURRENCE OF A SIGNIFICANT DEGREE OF POLYMERIZATION BY DIENE ADDITION OF SAID QUINOID STRUCTURES, STOPPING THE REACTION WITH A REDUCING AGENT SELECTED FROM THE GROUP CONSISTING OF SULFUR DIOXIDE, SULFUROUS ACID, SODIUM THIOSULFATE, AND POTASSIUM THIOSULFATE, TO CONVERT SAID O-QUINOID STRUCTURES INTO PYROCATECHOL STRUCTURES.