Analysis of the Leaves of Tussilago Farfara, Lin.
By CHARLES S. BONDURANT, PH. G.
(Some plants in the Asteraceae contain hepatotoxic pyrrolizidine alkaloids. Coltsfoot is among them. More info here: Livertoxic PAs --Henriette.)
(From an Inaugural Essay).
The leaves were carefully freed from the long petioles and other extraneous matter. On account of their tomentose character considerable trouble was experienced in reducing them to No. 80 powder. Moisture determined in a portion of the air-dried drug amounted to 7-8 per cent. This may include a small percentage of volatile oil which was also present.
Fifty grams (50 gm.) were taken for analysis. Complete exhaustion with petroleum spirit yielded 2.18 per cent solid matter at 100° C. On increasing the temperature to 110° C. an acrid volatile oil was driven off in small quantity. The residue after driving off volatile oil, yielded nothing to distilled water. Boiled with absolute alcohol, the solution, on cooling, deposited a small amount of waxy matter of low melting point. Caustic potash was added to the alcoholic solution and after boiling, diluting and acidifying, a small portion separated insoluble in water, showing presence of a small amount of resinous matter. That portion of the petroleum extract, insoluble in absolute alcohol, was caoutchouc, soluble in chloroform, bisulphide carbon and ether, not saponified with strong solution of potassa.
The residue of the original 50 gm. was next macerated with stronger ether until exhausted with that solvent, which extracted 2.63 per cent. solid matter sparingly soluble in distilled water, to which it imparted an intense bitter taste. This aqueous solution contained no tannin, and gave no reaction for alkaloids, but was found to readily reduce Fehling's solution after boiling with dilute hydrochloric acid and neutralizing, thus giving evidence of a glucoside. After evaporating this aqueous solution on a water bath to a small bulk and placing this over sulphuric acid for several days, a white amorphous solid had separated, quite bitter and inodorous, but on boiling with dilute sulphuric acid, a strong odor, similar to that of wetted leather, was evolved. Thus decomposed and neutralized, the liquid reduced Fehling's solution.
That portion of the ethereal extract insoluble in water was treated with hot absolute alcohol which failed to dissolve the whole of the residue. The alcoholic solution filtered and poured into a large quantity of acidulated water, separated a dark brown-reddish resin, which, on drying became brittle, dark red with concentrated sulphuric acid, whitish on the addition of water, and was soluble in concentrated solution of caustic potash. That portion insoluble in boiling absolute alcohol was found to be caoutchouc which had escaped extraction with petroleum spirit.
The residue after exhaustion with stronger ether was macerated for 24 hours with absolute alcohol and filtered. On evaporation an extract remained which amounted to 3.28 per cent., the greater portion of which was soluble in distilled water. The aqueous solution was free from alkaloids, with ferric chloride showed evidences of tannin, and with neutral lead acetate yielded a precipitate containing 2.64 per cent. of organic matter, while gelatin and alum precipitated 2.42 per cent., the difference being probably gallic acid.
The small portion not dissolved by distilled water from the alcoholic extract was found to be resinous and similar in character to that obtained in the ethereal extract.
The petroleum spirits, ethereal and alcoholic extracts were strongly colored green by the chlorophyll present in the leaves. The solutions were distinctly green by transmitted and dark red by reflected light.
The residue from the alcoholic treatment was dried and macerated with distilled water during 24 hours, then filtered and made up to known volume by passing distilled water through the filter. The extracted matter amounted to 11.22 per cent. The aqueous solution, treated with 2 vols. of absolute alcohol precipitated 3.42 per cent. of mucilage; the filtrate concentrated and treated with 4 vols. of absolute alcohol deposited 6.23 per cent. of dextrin and allied carbohydrates, and the filtrate from this on evaporation yielded saponin, insoluble in absolute alcohol, soluble in chloroform, turning purple with concentrated sulphuric acid and yielding frothing solutions with water.
The residue of the powdered leaves left after treatment with water was next treated with a 0.2 per cent. solution of caustic soda, the filtrate slightly acidified with acetic acid, and mixed with 3 volumes of 95 per cent. alcohol; the precipitate was dried at 100° C., weighed, incinerated, and after deducting the ash, gave 6.21 per cent. albuminous matter present.
The residue of the leaves not dissolved by caustic soda was treated with dilute hydrochloric acid, the filtrate neutralized with ammonia, the precipitate dried, and incinerated to calcium oxide, and calculated to calcium oxalate, amounting to 1.26 per cent.
The residue of the 50 gm. of powder, on being treated with distilled water and chlorine gas, lost 19.42 per cent. of lignin and incrusting substances, the dried residue of 28.43 per cent. constituting cellulose.
A qualitative examination was made of the ash weighing 17.10 per cent. of the powdered leaves; it contained potassium, calcium, magnesium, iron and aluminium, chlorides, phosphates, carbonates and silicates.