A-G-R1 CULTUR5. PC CV ,I

;L . ' U. S. Department of Agriculture, Forest Servic e

FOREST PRODUCTS LABORATOR Y In cooperation with the University of Wisconsi n MADISON, WISCONSIN ',S

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EFFECT OF PRETREATMENTS OF WOOD ON TH E LIGNIN DETERMINATION; DISTRIBUTION OF METHOXYLS IN WOO D By GEORGE J . RITTER Chemist and JAMES H . BARBOU R Junior Chemist ■.,/' AS S 4 min

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Published in INDUSTRIAL AND ENGINEERING CHEMISTR Y July 15, 193 5 •,.

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Various treatments have been proposed (2, 5, a) for wood previous to the : igniu determination by the 72 percent sulphuric-acid method . The purpose of such pretreatments has been to reduce the likelihood o f contaminating the lignin residue with decomposed extraneous materials . Pretreatments both with benzene-alcohol solution (5) and with alcohol and hc,t water (a) have been recommended for Nort h American woods . A pretreatment with 0 .5 percent sodium hydroxide ha s been recommended for Australian woods (2) . Although the three propose d pretreatments have merit for removing certain kinds of extraneous mate m 3 *NIP are, however, inadequate for removing other interferin g extraneous substances found in some woods . Other modifications (6, 1 , 10, 11, 12) of the sulphuric-acid method and a discussion (4) of th e effect of the alkaline pretreatment have been published .

G. M. Kuettel of the Forest Products Laboratory has demonstrate d that other troublesome extraneous materials, namely, catechol tannins , interfere with the lignin determination . The present paper proposes a modification of the sulphuric-acid method, which insures the removal o f catechol tannins by means of a preliminary treatment of the wood . It i s recognized that the method with its proposed modification may still b e inadequate _fox a a}aa .t ,ve lignin determination of some woods havin g unu '1 if still other extraneous materials . The proposed modification is based on the fact that catecho l tannins, which are incompletely soluble in the benzene-alcohol solutio n and hot-water pretreatments previously described for North American woods , are dissolved by pretreating the wood with 95 percent alcohol . when analyzing wood containing no tannins the proposed pretreatment of th e wood with alcohol is, of course, unnecessary ; however, when analyzin g woods in which the twnni. .n runt t is unknown it is a safeguard . 1 -Presented before the Division of CelUse Chemistry at the g9th Meeting of tbm American Cheal Society, .ty, April 22-26, 1 935 . 4

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three preliminary extractiv e ecommended conta' extraction with alcoho l ;cod . The fir s t con raction withel-cohol dMil6hol tannins ; the second , 00 aaad the third, an ex'emove #azi p :at L * ith hod o r00 s,ng water-soluble materials . , the solid extraneous mate ved t ted wood were absent afte r rial ta the cell! the wept for an occasi • bus indicating the remova l as f okactiv . The womb ~e remaining after the thre e rent sulphuric acid to dissolv e itiONOOMMI eated with ids eavi as a sc~ •#esidue . A The met

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are 4o .r the Determination of LignininWood

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s of

3 are weighed-

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ir corre ion

ferre# % a t #ner,

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desired, ~nin is' rh.e ash content (determined i n ,

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- ._est of the Metho d

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a obtained b y _r ding ti ed (5, 4n which i Cougar :ir > moil 1 .11

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bed werelkompare d icatioh e .~, ned according t o those r hot water fo r is substituteE s of (1) ligni n e made the the isolated lignin, an d j

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in the form of sawdus t ately in a tared alundum then eracted hours in a Soxhlet material is next extracted fo r -ume) . The solven t hol-benzene solution _IQ of by suction to re suction the residue washed 400 cc .of hot wate r ne n extracted for 3 metered, washed witer, and finally dried . ransferred to a large class-stoppered weighin g -ed with 25 cc .of 72 percent sulphuric acid a t ature it is maintained for 2 hours . The result rg:r to an Erlenmeyer flask, diluted with wate r and then boiled for 4 hours under a e is filtered on a tared alundum crucible , means of hot water, dried, and weighed . The 'elated on the basis of the oven-dry unextracted

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(3) the percentage of the total meior1 that is recoV, l i 3s . th e n-contadim t¢oodda, isolated lignin . Tha test was made on t a namely, r Od LoWOVrond and white e--l Table 1 t ht tifflE4A econtents as determ> ; is of th e proposed met i.ord are Ii.gted in column 2 ; those obtai*nog 1 ro previousl y described methods (•, 3) are listed in . eolumns 3 oad. 5, respectively ; and those obtained by substituting hot alcohol for kmt - Ater A 4 pre pre treatment of the wood are listed in co1W treatment . Discussion of Result s Apparent. L.

;-nnYields

There is a pt5sitive increase in the apparent 7:ignin ytie'l i n going stepwise in Table 1 from eolum . 2 to volkW*n 5~. Iz then. elves the y offer no explanation as to whether the differences in yiel,s ; fir 4** to' an inclusion of increasing amounts of contaminants as the yields tLOr''O.pAke . or to a removal of 4ec-reasing . amounts of 1i;g i . Aids incr., They are useful, however, when correlated with. the data ial'Table 2,• k showing that the changes in the apparent lignin e e t4 after erent extractive treatments of the wood are due to an inc] o . amounts of contaminants.. Defor'e it can be demo istit ted tha. 1 percentages offoreig . r ateTjais are included in the hii . heir area it is necessary to compare scme characteristie chem=ical pxaper&y ' 5th , apparent lignin residues, such as the met,ol c!onrt•ent .

Mme

Netho

1 Content of the Lignin Residue s

The methoxyl content of the lignin was : lac d fur cY e ;0t ing the lignin residues, which were isolated by Ole Cdi modifies, oo the method as indicated in the column headings of - ' .gble 1 . The rio0kIlt s for comparison are recorded in Table 2 . The melkoxyl content determined by the Zeisel method '('1) i s highest in colurat 2 and successively decreases in columns 3, 4, and 5 . These results considered in conjunction with those in the correspondin g columns of Table 1 show that the higher methoxyl contents of the ligni n residues are associated with the lower apparent lignin yields . Suc h data suggest the presence of larger amounts of materials having a lo w methoxyl content as the percentages of the apparent lignin yields in creases . That such is the condition can be shown by' calculating . the methoxyl content of the various apparent lignin residues on a commo n basis as is shown in Table 3 . These calculated data, made on th e basis of the unextracted wood, result from multiplying the methoxy l content of Table 2 by the content of its parent substance, the ligni=n- , in Table 1 . Inasmuch as Ite 4 gag In Table 3 are a composite of the methoxyl and the lignin yields, they 4wrefore include any errors that might hav e beau made during the methoxyl and the lignin determinations . A slight R1069

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eroctit in 0100 of the procedures would acciMpO for the lowest methoxyl val-ae fib +e.cit i column 5 of Table j . It would seem that thi s value s ro :d tfgtxal t; aibtrs or even be slightly higher since, beside s met y1i li in, Aight .include methoxyls associated wit h lemon; T tities + .'extraw4i us mzAerials than are present in the othe r i,dues ; Allow ±, r sliiht m In the determinations, th e flat. f;07ar Tales IN* the methb* cont vkp , nin residues from eac h iew IXO$A%,, t;hmy° alre within experi 174 04 4120 in cl ue t eemen mental accuracy„ It is,. gh0eestre, concluded from these results tha t the diffeltenee in l._ a y cello . etueen columns 2, 3, L . , Sd 5 in Tabl e a ials having fiery 1it'tT4l t! r 1 is dumi to the present .off+ t .*m mel tract of t any, methoxyl . The preseuv6 'big' i5nixc tk X03 was skew clua ti~wlj': by means of . n ab o dria saltss abdameting the pro p O that at least' some e'f tyre ; rims are rerm a alcoholic t moeiext of the woodN

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s thoxyl It. Its apprgp n. ie to tientiwta here that tea some w $ a. 'c ted 1441 the t rvimao s. .Na i k4is holm eL iamise :as well ,s v i:t t i 14gViOw The di {, `r -,;ion o f re- ho is 14=1 these three ;d.r'ood and . white oak i 4 f i*OKt c # s1 in ;bete i+. &Bo

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ion Of tffaft rl

Methoxyl do4opmi .o e wage on tk fnextracted r is wood ex ct.ed with a.l g'®ho1,, alcohol- nzene soluflan , o4, and tie "a; . d- 1iga n% Mae met1ao l conteA of r-ials ana %t 00le ila t wiao . calciuat.e-d by difference * _-

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Data t~n lines 40.1 am& 4 mf 'mobile )$ are 'E result of expel 4entattUQA1 .. :ose in 1 ts . & fined by suction ; thos a . 5 wVre o p in 14fa6 to. 9, i*el! of by cal ation la ze w9o dt • lze methoxyl eon,t -of the. eztx • tlaterials i .s hi$4 6oAp%WOd with that of th e carrespondz g result i i. .te od'k (line 3') . A p >,bility of removing some hereto-Q- l.osixmatreri from tie we•od d ' ,pvetreatment • ,s proved an hat watt is melegmized: NoTpelver'o Astil the pasa. ' content of th e iiegrericmetiail F ac't, the late pe .init4g to time owtilsq0t Te' ous matarial ma 3-ta~lAxe &i a a Minden as recorded i n ho--7~ Tablz `#, _ ild i .,nstitutw thepart 1*6 met :, %racte d R T • -• _ i.der w' th e Wit I g X~ thoxyl bine a e r-owoo . o oce 6se is '' ■comb ti s ; .,+_ white oak holocellul.ose (line of th9 ilia ~aa, the that soak t n r ,

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Summary and Conclusion s The accuracy of the determination of lignin in wood by means o f the 72 percent sulphuric-acid method is affected by the amount and kin d of extraneous materials incompletely removed from the wood by means o f preliminary treatments . Successive extractions of mood with 95 percent alcohol, alcohol benzol solution, and hot water make the 72 percent sulphuric-acid metho d for the lignin determination more adaptable to North American woods . If the kind and amounts of extraneous materials present in a given species of wood are known, the preliminary treatments can b e modified accordingly. For example, if catechol tannins are absent th e extraction with 95 percent alcohol may be eliminated . The methoxyl groups of redwood and white oak woods are dis tributed among the extraneous materials, the holocellulose, and th e lignin . Literature Cite d (1) Bray, M . W ., Paper Trade Jour ., g7, 59-68 (1928) . (2) Cohen, W . E ., and Dadswell, H . E . , "Chemistry of wood, Part 1 1 " Melbourne, Commonwealth of Australia, Council of Scientific an d Industrial Research, 1931 . (3) Friedrich and Salzberger, Monats ., 53 and 5L ,98 9 (1 929) . (4) Harris, E . E ., Ind . Eng . Chem ., Anal . Ed ., 5, 105 (1933) . (5) Mahood, S . E ., and Cable, D . E ., Ind . Eng . Chem ., 14, 933 (1922) . (6) Norman, A . G ., and Jenkins, S. H ., Biochem . Jour ., 28, 21+7 (193+) . (7) Peterson, C . J ., and Walde, A . W ., Ind . Eng . Chem ., Anal . Ed., ,

216 (1932) .

(8) Ritter, G . J ., and Kurth, E . F ., Ind . Eng . Chem ., 25, 1250 ( 1 933) . (9) Ritter, G . J ., Seborg,' R . M ., an_d Mitchell, R . L ., Ibid . , 4, 202

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(1932) .

(10) Ross, J . H ., and Hill, A . C ., Pulp & Paper Mag . Can ., 27, 15, 541

(1 929) .

(11) Schwalbe, H ., Papier-f abr . , 23, 171- (1925) . (12) Sherrard, E . C ., and Harris, E . E ., Ind . Eng . Chem ., 24, 103 (1932) . (13) Sherrard, E . C ., and Kurth, E . F ., Jour . Amer . Chem . Soc ., 51, 312 9

(1929) .

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Table 1 .--Effect of the removal of extractives on the lignin yield s obtained from woo d (Percentages based on oven-dry (105° C .) weight of the unextracted wood . ) Lignin in wood extracted with - Species

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Redwood (heartwood)

Average

White oak 4

Average

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t Alcohol, Alcohol: alcohol- : benzene and :benzene, and : hot water hot water : 2

: Alcohol . Alcohol : and . . benzene : alcohol- : only : benzene .

3

. ( 29 .76 ( 30 . g U( 30 .54 . ( 30 .77 ( 30 .36 ( 30 . 147 ( 30 .58 . ( 30 .32 ( 30 . 49 . ( 30)42 30 .31

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31 .13 31 .20 30.90 30.96 31 .00 31 .00 31 .02 31 .02 31 .02

4

5

31 .75 31 .85 31 .83 31 .56 31 .71

. 32 .50 : 32 .60 32 .28 . 32 .06 : 32 .16 32 .28 32 .08 32 .03 31 .99 :

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30 .44

31 .03

31 .74

: 32 .24

. ( 22 .99 : ( 22 .56 ( 22 .81 ( 22 .76 ( 22,92 (

23 .35 23 .50 23 .11 23)48 23 .15

24 .74 24 .87 24 .80 24 .81 24 .70

26 .0)4: 26 .14 : 26 .1 6 : 26 .1 7 26 .07 25 .99

22 .81

23 .32

24 .78

: 26 .10

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Table 2 .--Methoxyl content of lignin isolated from wood subjected t o different extractive treatment s (Percentages based on the oven-dry (105° C .) weight of the isolated lignin . ) Methoxyl in lignin isolated from woo d extracted with -Species

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White oak :

: Alcohol, : Alcohol : alcohol- : benzene onl y : benzene : ;

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5

13 .41+ 13 .43 13 .52

13 . 1+3 13 . 3 1+ 13 .29

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12 .6 8 12 .79 12 .7 5

13 .6 1+

13 . 1+6

13 .35

:

12 .7 1 +

( 20 .10

19 .14

( 20 .10 (

19 .13

18 .39

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17 .8 9 17 .8 8 17 .8 9

20 .10

19 .13

18)+3

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17 .89

( 13 .75 ( 13 .57

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: Alcohol. benzene and water 3

( 13 .61

Redwood (heartwood)

Average

Alcohol, alcoholbenzene and water

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jected t o

Table 3 .--19fethoxiTI contentoflignin ;...1);pAsAL different extrabtive tr t2arr

(Percentages based on oven-dry (105° C .) t oigK of the -u xtrac1 ' ror.0 Methoxyl in lignin isolated from woo d extracted with - Species

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: Alcohol, . alcoholbenzene, : water

: Alcoholbenzene, water

: Alcohol, : Alcohol : alcohol- : benzen e : benzene : onl y

Redwood (heartwood)

1+.15

4 .17

4 .23

4.l 0

White oak

4+.58

4.46

4+ .56

4.67

Table 4 .--Distribution ofmethoxyl in woo d (Unless otherwise specified, percentages are based on the oven-dry (105° C, ) weight of the unextracted wood . ) : Redwood : White oak

Wood fractions 1. Methoxyl in 2. Methoxyl in Methoxyl in . Methoxyl in 5. Methoxyl in 6.

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unextracted wood 5 .71 extractedi wood 4 .70 y . .. extraneous materials (1 - 2) 1 .01 : lignin from extracted wood 4 .17 : holocellulose from extracted woo d (2-- 4) : .53 Percent of total wood methoxyl in extraneous materials (3 1) 17 .70 Percent of total wood methoxyl in lignin-(4 . 1) . : 73 .00 Percent of total wood methoxyl in holocellulose (5 - 1) 9.30 Percent of extracted wood methoxyl in holocellulose (5 . 2) : 311 .25 Percent of extracted wood mOthOxyl in lig Ti n ( ''a - 2) : 3SS .72

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6 .3 S 5 .91 .47 4.55

:

1 .3 6

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7 .4 0 71 .3 0

:

21 .30

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323 .02

:

376 .9 5

-Wood was extract@d consecutively with a&€ , a'l~bl ] --~2~ eno eV' then washed with alcohol to remove berg e, &ad fi . extras hot water . . -Lignin was isolated from wood extracted

o 3-Calculated on the basis of the extracted weed . a

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