DIE CHEMIE DER LIGNOCELLULOSEN—EIN NEUER TYPUS.
W. C. Hancock and O. W. Dahl (Berl. Ber., 1895, 1558).
Chemistry of Lignocelluloses—A New Type.
The stem of the aquatic Æschynomene aspera offers an exceptional instance of structural modification to serve the special function of a 'float,' 1 grm. of substance occupying an apparent volume of 40-50 c.c. This pith-like substance is morphologically a true wood (De Bary), and the author's investigations now establish that it is in all fundamental points of chemical composition a lignocellulose, although from its colour reactions it has been considered by botanists to be a cellulose tissue containing a proportion of lignified cells. Thus the main tissue is stained blue by iodine in presence of hydriodic acid (1.5 s.g.), and the colour is not changed on washing. The ordinary lignocelluloses are stained a purple brown changed to brown on washing. The reactions with phloroglucol and with aniline salts, characteristic of these compounds, is only faintly marked in the main tissue, though strongly in certain individual cells.
The following quantitative determinations, however, establish the close similarity of the product to the typical lignocelluloses:
Elementary Analysis.—C 46.55, H 6.7. Furfural 11.6 p.ct., of which there remained in the residue from alkaline hydrolysis (71 p.ct.) 8.0, i.e. about 70 p.ct. The distribution of the furfuroids is therefore not affected by the alkaline treatment.
Chlorination.—The substance (after alkaline hydrolysis) takes up 16.9 p.ct. Cl, of which approximately one-half is converted into hydrochloric acid.
Methoxyl.—O.CH3 estimated = 2.9 p.ct.
Ferric Ferricyanide Reaction.—Increase of weight due to blue cyanide fixed (1) 75 p.ct., (2) 96 p.ct. Ratio, Fe: CN = 1: 2, 4.
Hydroxyl Reactions.—In the formation of nitric esters and in the sulphocarbonate reaction the substance gave results similar to those obtaining for the jute fibre.
These results establish the general identity of this peculiar product of plant life with the lignocelluloses, at the same time that they show that certain of the colour reactions supposed to characterise the lignocelluloses are due to by-products which may or may not be present.
(p. 172) Composition of Elder Pith.—In a systematic investigation of the celluloses in relation to function we shall have to give special attention to the parenchymatous tissues of all kinds. These are, for structural reasons, not easily isolated, for which reason and their generally 'inferior' functions they do not present themselves to chemical observation in the same obvious way as do their fibrous relatives. The pith of the elder, however, is readily obtained in convenient masses, and a preliminary investigation of the entire tissue has established the following points:
The reactions of the tissue are in all respects those of the lignocelluloses.
Composition.—Ash, 2.2 p.ct.; moisture in air-dry state, 12.3 p.ct. Alkaline hydrolysis (loss): (a) 14.77, (b) 17.84. Cellulose (yield), 52.33 p.ct. Nitrate-reaction complicated by secondary reactions and yields low, 90.95 p.ct. Sulphocarbonate reaction: Resists the treatment, less than 10 p.ct. passes into solution.
Furfural.—The original tissue yields 7.13 p.ct.; the residue from alkaline hydrolysis (b) 5.40 p.ct.
This tissue is, therefore, a lignocellulose having the chemical characteristics typical of the group, but of less resistance to hydrolytic actions.
The investigation will be prosecuted in reference to the cause of differentiation in this latter respect. Probably the pectocelluloses are represented in the tissue.
The Insoluble Carbohydrates of Wheat (grain).
H. C. Sherman (J. Amer. Chem. Soc., 1897, 291).
(p. 171) This is a study of the constituents of the cell-walls of wheat grain. Bran was taken as the most convenient form of the raw material, being freed from starch by treatment with malt extract, and further treated (1) with cold dilute ammonia, (2) cold dilute soda lye (2 p.ct. NaOH), and (3) boiling 0.1 p.ct. NaOH. The product retained only 1.25 p.ct. proteids, and yielded 15.62 p.ct. furfural.
Acid Hydrolysis.—The product was boiled 30 mins. with dilute acid (1.25 p.ct. H2SO4), and the solution boiled until the Fehling test showed no further increase of monoses. At the limit the reducing power of the dissolved carbohydrates was 91.3 p.ct., that of dextrose. Converted into osazones the analysis showed them to be pure pentosazones. The hemicellulose of wheat is, therefore, according to the author, pure pentosane.
Residue.—This was a lignocellulose yielding 11.5 p.ct. furfural. It was subjected to a series of treatments with ferric ferricyanide, and the proportion of Prussian blue fixed was determined by increase of weight, viz. from 10 p.ct. to 47 p.ct. according to the conditions. The results confirmed those of Cross and Bevan first obtained with the typical lignocellulose (jute).
Chlorination.-The residue was boiled with dilute alkali, washed, and exposed to chlorine gas. The resulting lignone chloride was isolated by solution in alcohol, &c. It yielded 26.7 p.ct. Cl on analysis. In this and its properties it appeared to be identical with the product isolated by Cross and Bevan from jute, with the empirical formula C19H18Cl4O9.
Cellulose was isolated from the residue by three of the well-known methods, and the following comparative numbers are noteworthy:
| Method | F. Schulze Dil. HNO3 KClO3 | Lange Fusion KOH | Cross and Bevan Chlorine, &c. |
| Cellulose p.ct. obtained | 66.0 | 39.3-43.1 | 66.5 |
| Furfural p.ct. of cellulose | 7.0 | 3.96 | 5.62 |
| Residual nitrogen | 0.22 | 0.03 | 0.00 |
| Ferricyanide reaction, Prussian blue fixed | 6.04 | 0.89 | 0.92 |
The author remarks: 'It is evident no one feature can be urged as a criterion in judging between the methods, but all must be taken into consideration. Such a comparison shows the superiority of the chlorination method.'
The cellulose is not of the normal (cotton) type, since on treatment with sulphuric acid it dissolves with considerable discolouration, but only to the extent of about 80 per cent. The dissolved monoses converted into osazones were found to consist of hexoses only. The cellulose treated with caustic soda solution (5 p.ct. NaOH) in the cold yielded 20 p.ct. of its weight of soluble constituents, but as the residue yielded 3.34 p.ct. furfural the attack of the alkali is by no means confined to the furfuroids.
Animal Digestion of the Constituents of Bran.—Observations on a steer fed upon wheat bran only established the following percentage digestion of the several constituents:
| Soluble carbohydrates | 96.9 |
| Starch | 100.0 |
| Free pentosanes | 60.2 |
| Cellulose | 24.8 |
| Lignin complex | 36.7 |
| Proteid | 82.96 |
| Ether extract | 42.73 |
| _____________________ | ______ |
| Nitrogen-free extract | 76.08 |
| Crude fibre | 32.21 |