Researches on Cellulose Part 12

[7] The change is empirically represented as

C_{6}H_{12}O_{6} + HBr - 4H_{2}O = C_{6}H_{5}O_{2}Br.

SECTION IV. CELLULOSE GROUP, INCLUDING HEMICELLULOSES AND TISSUE CONSt.i.tUENTS OF FUNGI

VERSUCHE ZUR BESTIMMUNG DES GEHALTS EINIGER PFLANZEN UND PFLANZENTEILE AN ZELLWANDBESTANDTEILEN AN HEMICELLULOSEN UND AN CELLULOSE.

A. KLEIBER (Landw. Vers.-Stat., 1900, 54, 161).

~ON THE DETERMINATION OF CELL-WALL CONSt.i.tUENTS, HEMICELLULOSES AND CELLULOSE IN PLANTS AND PLANT TISSUES.~

In a preliminary discussion the author critically compares the results of various of the methods in practice for the isolation and estimation of cellulose. The method of F. Schulze [digestion with dil. HNO_{3} with KClO_{3}--14 days, and afterwards treating the product with ammonia, &c.] is stated to be the 'best known' (presumably the most widely practised); W. Hoffmeister's modification of the above, in which the nitric acid is replaced by hydrochloric acid (10 p.ct. HCl) is next noted as reducing the time of digestion from 14 days to 1-2 days, and giving in many cases higher yields of cellulose. The methods of treating with the halogens, viz. bromine water (H. Muller), chlorine gas (Cross and Bevan), and chlorine water, are dismissed with a bare mention, apparently on the basis of the conclusions of Suringar and Tollens (_q.v._). The method of Lange, the basis of which is a 'fusion' with alkaline hydrates at 180, and the modified method of Gabriel, in which the 'fusion' with alkali takes place in presence of glycerin, are favourably mentioned.

These methods were applied to a range of widely different raw materials to determine, by critical examination of the products, both as regards yield and composition, what t.i.tle these latter have to be regarded as 'pure cellulose.'

This portion of the investigation is an extension of that of Suringar and Tollens, these latter confining themselves to celluloses of the 'normal' groups, i.e. textile and paper-making celluloses. The present communication is a study of the tissue and cell-wall const.i.tuents of the following types:--

1. Green plants of false oat gra.s.s (_Arrhenatherium, E._).

2. Green plants of lucerne (_Medicago sativa_).

3. Leaves of the ash (_Fraxinus_).

4. Leaves of the walnut (_Juglans_).

5. Roots of the purple melic gra.s.s (_Molinia caerulea_).

6. Roots of dandelion (_Taraxac.u.m officinale_).

7. Roots of comfrey.

8. Coffee berries.

9. Wheat bran.

These raw materials were treated for the quant.i.tative estimation of cellulose by the method of Lange (b), Hoffmeister (c), and Schulze (d), and the numbers obtained are referred for comparison to the corresponding yields of 'crude fibre' (Rohfaser) by the standard method (a).

As a first result the author dismisses Lange's method as hopeless: the results in successive determinations on the same materials showing variations up to 60 p.ct. The results by c and d are satisfactorily concordant: the yields of cellulose are higher than of 'crude fibre.'

This is obviously due to the conservation of 'hemicellulose' products, which are hydrolysed and dissolved in the treatments for 'crude fibre'

estimation. A modified method was next investigated, in which the process of digestion with acid chloroxy- compounds (c and d) was preceded by a treatment with boiling dilute acid. The yields of cellulose by this method (e) are more uniform, and show less divergence from the numbers for 'crude fibre.'

The author's numerical results are given in a series of tables which include determinations of proteids and ash const.i.tuents, and the corresponding deductions from the crude weight in calculating to 'pure cellulose.' The subjoined extract will ill.u.s.trate these main lines of investigation.

___________________________________________________________ Crude Fibre Pure Cellulose _____________ ____________________________ Raw Material Weende Hoffmeister Hoffmeister, Method. Method. modified by (a) (c) Author. (e) ________________ _____________ _____________ ______________ Oat gra.s.s 30.35 34.9 31.5 Lucerne 25.25 28.7 20.5 Leaves of ash 13.05 15.4 13.8 Roots of melic 21.60 29.1 21.4 Coffee beans 18.30 35.1 23.3 Bran 8.2 19.3 9.3 ________________ _____________ _____________ ______________

The final conclusion drawn from these results is that the method of Hoffmeister yields a product containing variable proportions of hemicelluloses. These are eliminated by boiling with a dilute acid (1.25 p.ct. H_{2}SO_{4}), which treatment may be carried out on the raw material--i.e. before exposure to the acid chlorate, or on the crude cellulose as ordinarily isolated.

~Determination of Tissue-const.i.tuents.~--By the regulated action of certain solvents applied in succession, it appears that such const.i.tuents of the plant-complex can be removed as have no organic connection with the cellular skeleton: the residue from such treatments, conversely, fairly represents the true tissue-const.i.tuents. The author employs the method of digestion with cold dilute alkaline solutions (0.15 to 0.5 p.ct. NaOH), followed by exhaustive washing with cold and hot water, afterwards with cold and hot alcohol, and finally with ether.

The residue is dried and weighed as crude product. When necessary, the proportions of ash and proteid const.i.tuents are determined and deducted from the 'crude product' which, thus corrected, may be taken as representing the 'carbohydrate' tissue const.i.tuents.

~Determination of Hemicelluloses.~--By the process of boiling with dilute acids (1.25 p.ct. H_{2}SO_{4}) the hemicelluloses are attacked--i.e.

hydrolysed and dissolved. The action of the acid though selective is, of course, not exclusively confined to these colloidal carbohydrates. The proteid and mineral const.i.tuents are attacked more or less, and the celluloses themselves are not entirely resistant to the action. The loss due to the latter may be neglected, but in calculating the hemicellulose constants from the gross loss the proteids and mineral const.i.tuents require to be taken into account in the usual way.

QUANt.i.tATIVE SEPARATION OF HEMICELLULOSE, CELLULOSE, AND LIGNIN.

PRESENCE OF PENTOSANES IN THESE SUBSTANCES.

WILHELM HOFFMEISTER (Landw. Versuchs-Stat, 1898, 50, 347-362).

(p. 88) The separation of the cellulose-like carbohydrates of sunflower husks is described.

In order to ascertain the effect of dilute ammonia on the cellulose substances of lignin, a dried 5 p.ct. caustic soda extract was extracted successively with 1, 2, 3, and 4 p.ct. sodium hydroxide solution. Five grams of the 2 p.ct. extract were then subjected to the action of ammonia vapour; the cellulose did not completely dissolve in six weeks.

Cellulose insoluble in caustic soda (32 grms.) was next extracted with ammonia, in a similar manner, for 10 days, dried, and weighed. 30.46 grms. remained, which, when treated with 5 p.ct. aqueous caustic soda, yielded 0.96 grm. (3 per cent.) of hemicellulose.

When cellulose is dissolved in Schweizer's solution, the residue is, by repeated extraction with aqueous sodium hydroxide, completely converted into the soluble form. On evaporating the ammonia from the Schweizer's extract, at the ordinary temperature and on a water-bath respectively, different amounts of cellulose are obtained; more hemicellulose is obtained, by caustic soda, from the heated solution than from that which was not heated. In this operation the pentosanes are more influenced than the hexosanes; pentosanes are not always readily dissolved by caustic soda, and hexosanes are frequently more or less readily dissolved. Both occur in lignin, and are then undoubtedly indigestible.

These points have to be considered in judging the digestibility of these carbohydrates.

A comparison of a.n.a.lyses of clover, at different periods, in the first and second years of growth, shows that both cellulose (Schweizer's extract) and lignin increase in both const.i.tuents. In the second year the lignin alone increased to the end; the cellulose decreased at the end of June. In the first year it seemed an absolutely as well as relatively greater amount of cellulose, and lignin was produced in the second year; this, however, requires confirmation. The amount of pentosanes in the Schweizer extract was relatively greater in the second than in the first year, but decreased in the lignin more in the second year than in the first: this result is also given with reserve.

DIE CONSt.i.tUTION DER CELLULOSEN DER CEREALIEN.

C. F. CROSS, E. J. BEVAN, and C. SMITH (Berl. Ber., 1896, 1457).

~THE CONSt.i.tUTION OF THE CEREAL CELLULOSES.~

(p. 84) Straw cellulose is resolved by two methods of acid hydrolysis into a soluble furfural-yielding fraction, and an insoluble fraction closely resembling the normal cellulose. (a) The cellulose is dissolved in sulphuric acids of concentration, H_{2}SO_{4}.2H_{2}O, H_{2}SO_{4}.3H_{2}O. As soon as solution is complete, the acid is diluted. A precipitate of cellulose hydrate (60-70 p.ct.) is obtained, and the filtered solution contains 90-95 p.ct. of the furfuroids of the original cellulose. The process is difficult to control, however, in ma.s.s, and to obtain the latter in larger quant.i.ty the cellulose (b) is digested with six times its weight of 1 p.ct. H_{2}SO_{4} at 3 atm.

pressure, the products of the action being (1) a disintegrated cellulose retaining only a small fraction (1/12) of the furfural-yielding groups, and (2) a slightly coloured solution of the hydrolised furfuroids. An investigation of the latter gave the following results: By oxidation with nitric acid no saccharic acid was obtained; showing the absence of dextrose. The numbers for cupric reduction were in excess of those obtained with the hexoses. The yield of ozazone was high, viz. 30 to 40 p.ct. of the weight of the carbohydrate in solution. On fractionating, the melting-points of the fractions were found to lie between 146 and 153. Ultimate a.n.a.lysis gave numbers for C, H, and N identical with those of a pentosazone. The product of hydrolysis appears, therefore, to be xylose or a closely related derivative.

All attempts to obtain a crystallisation of xylose from the solution neutralised (BaCO_{3}), filtered, and evaporated, failed. The reaction with phloroglucol and HCl, moreover, was not the characteristic red of the pentoses, but a deep violet. The product was then isolated as a dry residue by evaporating further and drying at 105. Elementary a.n.a.lysis gave the numbers C 44.2, 44.5, and H 6.7, 6.3. Determinations of furfural gave 39.5 to 42.5 p.ct. On treating the original solution with hydrogen peroxide, and warming, oxidation set in, with evolution of CO_{2}. This was estimated (by absorption), giving numbers for CO_{2}, 19.5, 20.5, 20.1 p.ct. of the substance.

The sum of these quant.i.tative data is inconsistent with a pentose or pentosane formula; it is more satisfactorily expressed by the empirical formula

O / C_{5}H_{8}O_{3} CH_{2}, / O

which represents a pentose monoformal. Attempts to synthesise a compound of this formula have been so far without success.

UEBER EINIGE CHEMISCHE VORGaNGE IN DER GERSTENPFLANZE.

C. F. CROSS, E. J. BEVAN, and C. SMITH (Berl. Ber., 1895, 2604).

~THE CHEMICAL LIFE-HISTORY OF THE BARLEY PLANT.~

(p. 84) Owing to the presence of 'furfuroids' in large proportion as const.i.tuents of the tissues of the stems of cereals, these plants afford convenient material for studying the problem of the const.i.tution of the tissue-furfuroids, as well as their relationship to the normal celluloses. The growing barley plant was investigated at successive periods of growth. Yield of furfural was estimated on the whole plant and on the residue from a treatment with alkaline and acid solvents in the cold such as to remove all cell contents. This residue is described as 'permanent tissue.' The observations were carried out through two growing seasons--1894-5--which were very different in character, the former being rainy with low temperature, the latter being abnormal in the opposite direction, i.e. minimum rainfall and maximum sunshine. The barley selected for observation was that of two experimental plots of the Royal Agricultural Society's farm, one (No. 1) remaining permanently unmanured, and showing minimum yield, the other (No. 6) receiving such fertilising treatment as to give maximum yields.

The numerical results are given in the annexed tables:

Table Headings:

A: Date B: Age of Crop C: Plot D: Dry Weight E: Furfural p.ct. of dry weight (a) F: Permanent tissue p.ct. dry weight G: Furfural from permanent tissue H: P.ct. of tissue I: P.ct. of entire plant J: Ratio a : c