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T H E JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY
forming Na2S04.NaHS04 and finally Na2S04. We do not question this conclusion. We do maintain, however, that their implication that we might not have had Na2S04.NaHS04 but a salt higher in acid which several washings with 95 per cent alcohol had changed into this double salt is not justified. It is rather improbable that one could transform 108.2 g. of NaHS04.H20into 6 8 . 5 g. of Na2S04.NaHS04 by a few washings of well-defined large crystals with 95 per cent alcohol. Further, 108.2 g. of the monohydrate, which i s the amount required to give 68.5 g. of the double salt, contain 3 8 . 4 g. of acid, which is more than the amount present in the solution from which the crystals separated. We claim our calculations have been confirmed. Further, the fact that not only the yield of Na2SO4.NaHS04, but that of Na2SOI1which, aside from its small solubility, is not affected by D’Ans’ solution, corresponds to the calculated value argues in favor of our conclusion. The criticism cited would also refer to the solubility determinations of Foote4 on which the present calculations are based. Foote, however, had no difficulty in identifying the acid sulfates Na2S04 NaHS04 and NaHSOa.Hz0 even though he used D’Ans’ solution for removing mother liquor. The experiment on crystallizing NR&04. NaHSO4 cited in the present paper would likewise be open to their criti-
285
cism. Yet the double salt obtained is homogeneous and forms in well-defined crystals. Four different 5-g. samples gave 18.55, 18.55, 18 56, and 18.58 per cent of acid, which is rather better than one would expect from crystals of a higher acid salt which had been altered on the surface during the process of washing. In conclusion, we wish to emphasize a statement in a previous papera that OUT results and those of others10 point to the conclusion that the separation of Glauber’s salt is the better the lower the temperature. The lower temperature limit is the cryohydrio temperature for the particular niter cake in question. .This fact has been used to advantage in several patented processes. E. Hart” obtains granular sodium sulfate by dissolving niter cake in water and cooling the solution to -40”. H. 111. Dawson6 carries out the separation at -21”. At this temperature the residual solution is said to contain only 2 . 8 per cent sodium sulfate. From 10 tons of a 30 per cent acid niter cake he obtains 15 tons of Glauber’s salt. If, however, the operation is carried out at O”, 14 tons of this salt are obtained, while at + l o ” the yield is only 6 . 4 tons. Pascal, Comgt. rend., 164 (1917),628; Bull.
SOC.
chim., ‘25 (1919),
35. 11
U. S. Patent 1,258,895 (1918).
Contributions to Chemistry of Wood Cellulose’ I-Acetolysis
of Spruce Pulp
By Louis E. Wise2 and Walter C. Russell LABORATORIES OF THE NEWYORKSTATE COLLSGEO F FORESTRY AND THE CHEIICALDEPARTMENT OF SYRACUSE UNIVERSITY, SYRACUSB, N. Y.
The work recorded in this paper is the beginning of an inoestigation of the chemical properties of wood cellulose as compared with those of cotton cellulose. This part of the work was done on spruce sulfite pulp, which yields appreciable amounts of cellobiose octacetate on acetolysis, as does cotton. Experimental evidence is presented that normal cellulose is the precursor of cellobiose octacetate, and normal spruce cellulose yields the same amount of the octacetate as does normal cotton cellulose under identical conditions of acetolysis. The authors therefore consider that Hibbert’s formula may represent the constitution of normal spruce cellulose as well as that of normal cotton cellulose, and that their experiments present additional evidence that cellulose from the “lignocellulose” of wood and cotton cellulose may be identical.
OTWITHSTANDING the recent important contrithe butions to the chemistry of cotton cell~lose,~ general term “cellulose” as applied to woods, straw, etc., remains a very vague one. The desirability of an exact definition of “~1’oodcellulose” was recently pointed out by Dore4 who states that the cellulose of woods “has been commonly accepted as a group designation, signifying a residue remaining after successive treatments with chlorine and dilute sodium sulfite solution, until free from lignin derivatives.” A very similar definition has been assigned to wood cellulose by Schorger.6 Whereas this type of definition may act as a convenient
N
1 Presented before the Section of Cellulose Chemistry, at the 62nd Meeting of the American Chemical Society, New York, N. Y . , September 6 to 10, 1921. 2 Professor of Forest Chemistry. Hibbert, THISJOURNAL, 18 (1921), 334. 4 THISJOURNAL, i a ( I Q ~ o )266. , 6 I b i d . , 9 (1917), 567.
stop-gap, and stimulate certain types of practical research, it seems to us to retard fundamental progress in the cellulose field. It is further open to the follouring very serious objections: 1-It defines as cellulose a mixture of varying composition, isolated by a convenient but arbitrary analytical procedure. 2-It is not based on any comparison of the chemical properties of the substance in question with those of a standard cotton cellulose. 3-It makes for confusion in the general usage of the term “cellulose.”
Schorger6has shown in his very important series of analyses of some American woods, that there are wide variations in pentosan content in the so-called “wood cellulose.” It is quite evident that if the above definition of the cellulose of woods is accepted, we face the unpleasant possibility of a different cellulose for every species of wood, and that even in the same species of wood the composition of the cellulose (always accepting tthe above definition) may depend on the period of growth, on Flight modifications in the methods of isolation used, and even on the skill and experience of the analyst. When factors of this type enter into consideration, a definition becomes of very questionable scientific value. It might be urged that wood cellqlose would be better defined as a residue obtained by some such procedure R S the one mentioned by Dore-with a correction applied for the pentosan and inethylpentosan content of such a residue. In fact this appears to be the commonly accepted European pract,ice. Such a procedure, however, furnishes no experimental data that would throw light on the similarity or dissimilarity between the chemical constitution of wood cellulose and cotton cellulose. Without such experimental evidence it would be quite futile to attempt a redefinition of “wood cellulose.”
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The preliminary report of Herzog and Jancke6 has a very important bearing on this subject. These investigators applied the Debye and Scherrer Rontgen spectrographic method to a study of purified cotton, wood cellulose, and ramie fiber. In all cases, the celluloses showed interference bands corresponding to a rhombic system of crystals, and the same axial ratio was noted in all cases. The work of Heuser and Baedeker' is in substantial agreement with the hypothesis that normal wood and normal cotton cellulose are chemically identical. Wood cellulose, which had been purified by means of 17 per cent sodium hydroxide, was hydrolyzed with fuming hydrochloric acid by Willstritter and Zechmeister's8 method. A control experiment was carried out with cotton cellulose. In both cases, the rate of hydrolysis to glucose was very nearly the same, and the maximum yield of glucose was reached 16.5 hrs. after peptization of the cellulose. The object of our investigation was to obtain, if possible, further data that would indicate similarity or dissimilarity of the constitution of cotton and wood cellulose. Many recent fundamental investigations on cellulose serve to emphasize the importance of the acetolysis reaction when applied to cotton cellulose. The formation of cellobiose octacetate, while far from quantitative, has apparently a diagnostic value in indicating the presence of cellulose. As far as we know, cellobiose has not been obtained by the hydrolysis or acetolysis of polysaccharides other than cellulose.8 OstlO has shown that, under conditions of protracted acetolysis, cotton yields up to 37 per cent of cellobiose octacetate. Madsen" showed that 30 to 32 per cent of the cellobiose octacetate could be obtained in a short time period. This yield could be increased up t o 43 per cent of the theoretical yield by the saponification and subsequent re-acetolysis of the so-called dextrin acetates formed in the reaction. The recent investigations of Freudenberg12 indicate that a t least 61 per cent of the cotton cellulose molecule is composed of cellobiose residues. Although the cellobiose octacetate reaction, as applied to cotton, has been rather carefully studied, and has been applied to filter paper of uncertain history, it has hitherto apparently never been applied to a cellulose isolated from wood in a comparative study. We have, therefore, used this reaction in our preliminary study of wood cellulose and have applied it primarily to spruce sulfite pulp, as the first step in an investigation of the chemical properties of wood cellulose as compared with those of cotton. Our experiments are being continued with cellulose isolated from other coniferous woods and from certain hardwoods.
EXPERIMENTAL PART Thp method of acetolysis used in our work was essentially that of Klein13 a8 modified by Madsen." The material used was spruce sulfite pulp taken from a shipment sent to us through the courtesy of the Riordon Company, Ltd. Comparative experiments were made with surgical cotton, snipped into short threads. The pulp was shredded on a grater and screened through a 20-mesh sieve. Only those particles passing the sieve were used. The moisture content of the air-dried cotton was 5.3 per cent; that of the pulp 7.2 per cent. In the acetolysis reactions, 5 g. of air-dried sample were very gradually incorporated into a cold mixture of 20 g. of a 7
Ber., 63 (l920), 2162, through C. A . , 16 (19211, 1311. 2.angew. Chem. (Aufsatzteil), 34 (1921), 461.
Ber., 46 (1913), 2401. The "tunicin" of the tests of the ascidians (marine animals) yields cellobiose and is commonly accepted as being cellulose. 10 Ann., 398 (1913), 337. 1 1 Dissertation, Hannover, 1917, 16. 12 Ber., 64 (1921), 767. 18 2. angew. Chem., 24 (19111, 1127. 8
Q
Vol. 14, No. 4
redistilled acetic anhydride (b. p. 135" to 137" C.) and 5 g. of concentrated sulfuric acid, the mixture having been initially prepared a t a temperature well below 10". The elevation of temperature owing to the addition of the cellulose was also carefully controlled. The maximum temperature recorded in any of our experiments was 55", but in this case .the reaction mixture was immediately cooled to below 30". In other cases, the highest temperature was 40" to 50" C., and here again cooling was resorted to. After liquefaction of the reaction mixture had set in, the solut,ion was allowed to stand a t 25" to 27" C. for 6 to 7 days. Crystallization normally began after 3 days, and at the end of the 6-day period, both the cotton and the spruce pulp had been converted into a stiff crystalline paste. The latter was treated with 30 cc. of glacial acetic acid, warmed to 50", and immediately poured into 700 cc. of ice water. The white flocculent precipitate thus obtained, after standing for 0.5 hr., was filtered off on a Biichner funnel, washed with water until free from sulfates, and dried a t 90" to 100". It was then extracted with chloroform, the extract evaporated, and the residue dissolved in the minimum amount of boiling 95 per cent alcohol. The alcoholic solution in the case of the product derived from cotton was always clear. That derived from spruce, however, invariably yielded an opalescent solut,ion at this point. In either case the alcoholic solution was treated with a small amount of boneblack, and the solution filtered through a hot water funnel (with water heated to about 80"). TABLE I-ANALYTICAL DATAON P E R CENT
"Total cellulose" after single chlorination . , , . "Total cellulose" after four chlorinations. . "Normal cellulose" after treatment of original sample with NaOH (17.6%) "Normal cellulose" after one chlorination. "Normal cellulose" after four chlorinations, , , , . ,,
.. . . . . . . . . . .. . . . . . . . . . ........... .. . . . .. . . . .. . ...... .
MATERIALS
COTTON
USED (Dry basis)
SPRUCEPULP
98.1
96.2
96.9
94.7
97.2
80.8
91,s
76.2
83.5
68.7
The filtrates were allowed to crystallize in an ice loath. The crystals, which appeared homogeneous under the microscope, were filtered off, and the filtrates evaporated to 50 to 75 cc. Small amounts of crystalline material could usually be r e covered under these conditions. Further evaporation, however, caused the separation of a taffy-like resinous substanceno doubt the acetylated dextrins studied by Madsen. Melting-point determinations indicated that the crystalline product obtained from spruce was identical with that obtained from cotton. Both melted at 225.5" (uncorr.). In a preliminary experiment, cellobiose octacetate was prepared from filter paper by the method outlined by Haworth and Hiwt.14 In this case the substance also melted at 225.5' (uncorr.), and the melting point of this material mixed with that prepared from spruce pulp showed no depression. Madsen gives the melting point of cellobiose octacetate as 228" (corr.). The product obtained from spruce is thus shown to be cellobiose octacetate. I n several of our experiments, the yields of cellobiose octacetate from cotton and from spruce pulp were determined as carefully as possible. Madsen'sl6 highest yields of cellobiose octacetate were 5.8 to 6.2 g. from 10.0 g. of air-dried cotton. In our case the yield was 2.94 g. of the octacetate from 5 g. of air-dried cotton. In all cases, the yields of the octacetate from air-dried spruce pulp were appreciably lower than those from the same weight of air-dried cotton. These differences can best be discussed by reference to Table I, J. Chem. Soc., 119 (1921), 197. We refer to Madsen's highest yields, excluding those experiments in which further treatment was applied to the "dextrin acetates" formed in the reaction. 14
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which gives some analytical data on the materials used, and to Table 11, which gives yields of cellobiose octacetate. TABLE 11-COMPARISON
OF YIELDSOF CELLOBIOSE OCTACETATE OBTAINED COTTON AND FROM SPRUCE PULP COTTON SPRUCEPULP Anhydrous material used in acetolysis, grams. 4.74 4 64 ‘Normal cellulose” after treatment of original sample with 17.5% NaOH, grams. 4.60 3.74 Cellobiose octacetate obtained, grams. 2.942 2.149 Percentage of theoretical yield of octacetate calculated from normal cellulose coutent 30.5 27.4 FROM
......... ..... ............
....................
In the case of cotton the so-called “total cellulose” was determined by Sieber and Walters’ method16 (as outlined by Dore4). This involved four chlorinations and the results were somewhat, but not appreciably, lower than the amounts of ‘[total cellulose” that could be obtained when only one chlorination (followed by the usual sodium sulfite treatment) was used. It is interesting to note, however, that the successive chlorinations seriously affect the amount of so-called normal (or a-) cellulose in the cotton (when determined by the Cross and Bevan mercerization test). The normal cellulose content is appreciably lowered by repeated chlorination-which might reasonably be expected in the case of a gradual oxidation of cellulose with the formation of alkalisoluble products. A very similar picture is presented in the case of the spruce pulp. The differences between the “total cellulose” in the case of cotton and spruce pulp are not very great (approximately 2 per cent). On the other hand, whereas very little of the original cotton is soluble in alkali, the original spruce pulp loses nearly 20 per cent when treated with 17.5 per cent NaOH, as shown in Row 3 of Table I. It is evident that the “total cellulose” determination, while it gives a good index of the amount of cellulose that was present in the original sample (provided always this sample had not been subjected t o oxidation prior to the analysis), does not necessarily indicate the actual amount of cellulose at the end of such an analysis. It certainly does not give a true index of the cellulose content of material, the previous history of which would indicate that it had been subjected to vigorous oxidation. These facts have been considered in calculating the percentage yield of cellobiose octacetate. Theoretically 1 g. of “pure” cellulose would yield (if complete conversion could take place) 2.09 g. of cellobiose octacetate. It would be obviously incorrect to assume that the original pulp and cotton were “pure” cellulose, and it would be unjustifiable to base our yield on the “total cellulose” determinations on the two samples. The so-called total cellulose would contain some material in which (assuming Hibbert’s formula) the alcoholic hydroxyl groups had been oxidized, and such material would not yield cellobiose octacetate on acetolysis. Since the object of our experiments was that of a comparative study, it appeared best to have our yields based on the “normal” cellulose content of both the cotton and the spruce pulp. In formulating a working hypothesis we considered as normal cellulose that residue which remained after treatment with 17.5 per cent alkali without previous chlorination or sulfite digestion. Although this might appear to be an arbitrary assumption, it is more logical than one which takes as normal cellulose a residue obtained after one or more successive chlorinations. The assumption appeared justified, since the original cotton sample after chlorination gave no coloration with sodium sulfite, and since the coloration in the case of spruce pulp was very slight. This would indicate the presence of only small amounts of lignin. Assuming that the normal cellulose was in each Papier-Fabr., 11 (1913), 1179.
287
case the precursor of cellobiose octacetate, it appears from Table I1 that the yields of octacetate from normal spruce cellulose and from normal cotton cellulose are not so very different. EXPERIMENTS ON NORMAL CELLULOSE-Aseries of experiments were then undertaken with a view toward testing our working hypothesis. “Normal cellulose” from cotton and spruce pulp was actually prepared and acetolyzed. Snipped surgical cotton and grated spruce pulp were treated with a 17.5 per cent solution of sodium hydroxide, allowed to stand 0.5 hr., and subsequently washed with successive portions of water and dilute acetic acid, and finally washed until the rinsings were no longer acid. Each sample was then allowed to dry in air. The moisture content of the normal cotton cellulose thus obtained was 7.5 per cent; that of the normal wood cellulose was 7.8 per cent. The normal cotton cellulose contained 1.18 per cent pentosans; the normal spruce cellulose contained 1.25 per cent pentosans. Five-gram portions of the normal cellulose (from cotton or wood) were acetolyzed by the method already outlined, with but few modifications. In one set of experiments ( A, Table. 111) the acetolysis mixtures were heated for 2 hrs. a t 40’ to 50°, and were allowed to stand 8 days a t 15Oto 20’. The other acetolysis mixtures (B, Table 111)were similarly heated, but were allowed to stand at room temperature for 17 days. TABLE111-YIELDS OF CELLOBIOSE OCTACETATEFROM NORMALCOTTON AND NORMAL SPRUCE CELLULOSE. CORRECTED FOR PENTOSAN CONTENT NORMAL COTTON NORMALSPRUCE CELLULOSE CELLULOSE Set A Set B Set A Set B Anhydrous normal cellulose (corrected for pentosan con4.552 4.571 4.552 tent) grams.. 4.571 Cellobi&e octacetate yield, 2,7340 2.7290 2.6634 grams, ................... 2.6976 Cellobiose octacetate based on the theoretical yield, per 28.0 28.6 28.7 cent 28.2 Meltin points of sample? of cello%iose octacetate iso227.5” 226’ 227’ 228’ lated (uncorr.)..
............
.....................
..........
The crude octacetate was crystallized from 95 per cent ethyl alcohol, without preliminary extraction with chloroform. The yields given in Table I11 refer to the crystalline product thus obtained. Emphasis should be placed on the fact that very nearly identical conditions were maintained in each set of acetolysis experiments. While the maximum yield of cellobiose octacetate was never reached, the results in each set are strictly comparable. It is evident from these experiments that the grouping
CHZOH
I
CHIC--CHZOI-I occurs not only in cotton but also in the cellulose of spruce wood, and there is every evidence that the amounts of cellobiose that may be obtained by using a definite procedure in the acetolysis of either normal cotton or normal spruce cellulose are very nearly the same. It is, therefore, highly probable that Hibbert’s formula3 for cellulose applies equally as well to the normal cellulose obtained from spruce wood as it does to cotton cellulose.
