FORMULA: C15H10O4. MOLECULAR WEIGHT: 253.39.
Source and History.—Chrysophanic acid was discovered by Schrader, in 1819, in the Parmelia parietina, Linné, a common wall lichen. He obtained it impure, and named it "resinous yellow of wall lichens." It was found in this lichen in 1843, and purified by Rochleder and Heldt, who gave it the name chrysophanic acid, from its yellow color (Ann. der Chem. und Pharm., xlviii). Shortly after this, Schlossberger and Dopping decided the coloring matter obtained from rhubarb to be identical. This coloring matter had been known under the names of rheine, rheumine, rhabarberic acid, rhubarb yellow, etc., names doubtless given to impure forms of chrysophanic acid, emodin, especially, being intimately associated with it. Each of these substances are dissolved by benzin, the chrysophanic acid more freely. According to E. Bourgoin, chrysophanic acid is present, in small amount, in senna leaves, and may be obtained by extracting crude cathartin, with ether. It is likewise found in yellow-dock root, in small amount, and a prolific source of it is araroba (Attfield).
Preparation.—Chrysophanic acid may be prepared from araroba, as follows: Mix in a flask 1 part of araroba, in powder, with 8 parts of benzin, and bring to a boil; filter while hot, and when the liquid ceases to pass, return the undissolved matter to the flask, and add 8 parts of benzin; boil, and filter, as before. Mix the filtrates, and evaporate to dryness. Dissolve the yellowish powder in 16 parts of boiling alcohol, filter, and add to the filtrate 32 parts of cold distilled water. Allow this to stand for 24 hours, then separate the yellow precipitate, by means of a muslin strainer, or filtering paper, and dry by exposure to the atmosphere.
From RHUBARB, chrysophanic acid may be obtained by exhausting the coarsely-ground root with water, evaporating the solution to dryness, extracting the residuum with boiling benzin, then evaporating the benzin, and, finally, purifying the residue by solution in hot alcohol, and precipitation with water, the same as stated above, in procuring it from araroba. Thus obtained, it contains emodin, but is pure enough for all practical purposes. The yield from rhubarb is small.
Description.—When pure, chrysophanic acid is in golden-yellow needles, but considerable of that at present upon the market is in the form of a brownish-yellow powder. Subsequent investigations showed it to be dioxymethyl anthraquinone (C15H10O4), while emodin was ascertained to be trioxymethyl anthraquinone (C15H10O5).
Chrysophanic acid is volatile at high temperatures, is soluble to a slight extent in cold, and a little more freely in hot water. It dissolves readily in alcohol, ether, benzin, and glacial acetic acid, to which it imparts a yellow color. Cold sulphuric acid dissolves it without decomposition, and with the formation of a red color, from which solution water precipitates it in yellow flakes. It dissolves in alkaline solutions, with the production of a beautiful red color, from which solution excess of acids precipitates it, and the liquid becomes decolorized. It has but little taste and no odor. Its fusing point is at 162° C. (between 323° and 324° F.).
Action, Medical Uses, and Dosage.—Chrysophanic acid has been chiefly employed as a local application in certain cutaneous affections, as mentagra, eczema, herpes tonsurans, herpes circinati, psoriasis, acne rosacea, etc. It is generally applied in the form of an ointment, consisting of from 10 to 120 grains of the acid to 1 ounce of hot lard (360° F.), with which the acid must be thoroughly incorporated. The parts affected having been carefully washed, to remove fatty substances, and any existing scales (squamae) having been softened and carefully removed, this ointment is to be well rubbed in upon the parts, 2 or 3 times a day. The strength of the ointment, and the number of applications per day, will depend considerably upon the amount of irritation occasioned, as it frequently gives rise to more or less irritation, or even inflammation of the skin. When applied about the face and head, care should be taken to protect the eyes from its irritant action. Its use is often objected to by patients, on account not only of its staining the clothing and bed-clothes a dull purple color, but likewise of its giving a more or less dark purplish tint to the skin, and a yellow color to the hair, with which it comes in contact. Mr. Balmano Squire, of London, Eng., to whom we are indebted for a knowledge of this agent, states that a careful use of bleaching powder will remove the stains from clothing; and liquor potassae, considerably diluted with water, will, it has been stated, discharge the discoloration of the skin and hair. While rubbing it upon the parts, the fingers may be protected from discoloration by wearing india-rubber finger tips, or by rubbing the stained parts with benzol.
Internally, but little is satisfactorily known as to the effects of chrysophanic acid. In small doses, from 4 to 8 grains, it has occasioned vomiting and in doses of from 10 to 20 grains both vomiting and purging. The time of action varies from 4 to 24 hours after it has been taken, and persists, in many cases, for 2 or 3 days. Liquor potassa,, taken subsequently to the dose of the acid, appears to increase its activity. Napier states that psoriasis yielded to half-grain pills of chrysophanic acid administered 3 times a day, after meals, continuing the drug until its physiological effect, gastro-intestinal irritation, was felt. Arsenic and various local applications had been used without producing any good results. In one case as much as 9 grains in 24 hours were taken without deleterious effects.