Acidum Aceticum (U. S. P.)—Acetic Acid.

Botanical name: 

Related entries: Acetum.—Vinegar - Aceta.—Vinegars
Other tomes: Ellingwood - BPC

FORMULA: HC2H3O2=C2H3O.OH=CH3.CO2H. MOLECULAR WEIGHT: 59.86. "A liquid composed of 86 per cent, by weight, of absolute acetic acid [HC2H3O2=59.86] and 64 per cent of water"—(U. S. P.).
SYNONYMS: Acetyl hydrate, Hydrogen acetate.

Source.—Acetic acid is the most extensively used organic acid, and is obtained either by the oxidation of alcohol and aldehyde, or by the destructive distillation of wood and carbohydrates in general. This yields an impure pyroligneous vinegar, which is subsequently purified. The greater portion of the acetic acid of commerce is now derived from this wood vinegar. As early as 1648 Glauber was familiar with the fact that vinegar could be obtained by the destructive distillation of vegetable tissues, but did not know that the substance so obtained was identical with the vinegar derived from alcoholic products. This identity was subsequently established (1800) by Vauquelin and Fourcroy. In 1802 Thénard proved its existence in products of dry distillation of animal tissues. Stahl proposed in 1700 a method to obtain acetic acid from vinegar by exposing the latter substance to a freezing temperature, separating the ice from the stronger acid; another method he suggested was to neutralize with an alkali and to evaporate, then distilling with an equal amount of sulphuric acid. In 1759 Count de Lauraguais obtained a crystallized acetic acid in a distillate of cuprum acetate, then known as "copper spirit." The name glacial acetic acid was affixed to this substance by Löwitz (1793), who repeatedly distilled diluted acetic acid with powdered charcoal, and obtained thereby a crystalline acid by subjecting the product to a low temperature.

Preparation and Description.—In order to bring before the reader the processes of the production of acetic acid it will be necessary to allude to the production of crude pyroligneous acid by the destructive distillation of woody substances. We shall then present the three commercial forms of acetic acid now in common use, viz.: acetic acid, glacial acetic acid, and diluted acetic acid.

I. ACIDUM ACETICUM PYROLIGNOSUM. Acidum pyrolignosum. Pyroligneous acid, Pyroligneous vinegar.

Preparation.—Crude pyroligneous acid is one of the principal products formed in the destructive or dry distillation of wood; i. e., in the process of subjecting the wood to a red heat in a closed vessel, so that the air has no access. This is done at present in closed iron retorts, much on the same plan as the destructive distillation of coal is carried on in the manufacture of illuminating gas. The vapors are condensed in suitable vessels, and the incondensible, gaseous products frequently conducted back into the furnace. The liquid obtained separates upon standing into two layers—an upper, aqueous, and a lower, tarry layer, the latter furnishing the material from which creosote is obtained by rectification. It contains benzene and its homologues, naphthalene, retene, phenol, cresol, phlorol, pyrocatechol, guaiacol and homologues, and empyreumatic substances. The upper stratum is the crude pyroligneous acid of commerce, and is separated by mechanical processes. It contains in aqueous solution formic and acetic acids and their homologues, including capronic acid, methyl alcohol, acetone, acetates of methylamine, phenol, guaiacol, furfurol, and empyreumatic substances. From this liquid are obtained commercially: Acetic acid, acetone, and methyl alcohol. The first step of separation is that of fractional distillation of the crude pyroligneous acid. The first part coming over (10 per cent) is the alcoholic part, called wood naphtha, and consists of methyl alcohol, acetone, and methyl acetate, also containing allylic and other alcohols; then distills the acid part, called purified pyroligneous acid or rectified wood vinegar, amounting to 75 to 80 per cent. It is a yellowish or colorless acid fluid, possessing a smoky odor, which may be removed by agitating it with 2 or 3 per cent of benzin, and removing the latter by separation and distillation; then the aqueous residue will furnish an inferior table vinegar. The preparation of pure acetic acid from rectified wood vinegar will be described under "Acetic Acid." As to the quantities obtainable, 100 parts of wood yield from 20 to 35 per cent of gas, 3 to 9 per cent of tar, 35 to 45 per cent of crude pyroligneous acid, of which 3 to 9 per cent are acetic acid, and 20 to 30 per cent of charcoal. It has been found that the percentage of real acetic acid obtainable from diverse woods varies considerably; the bark yielding less than the wood, sound wood more than decayed wood, and stem woods yielding the greatest quantity, even more than the branch woods; foliage trees produce a greater yield of pure acid than needle-leaved species. Slow combustion is also conducive to a better yield. The average yield of acid liquor from 800 pounds of wood is about 300 pounds, or 35 gallons.

Description.—Crude pyroligneous acid is a dark-brown, sour liquid, of a smoky odor due to furfurol [C5H4O2], Meyer), holding in aqueous solution 4 to 7 per cent of acetic acid, empyreumatic oil, creosote, and pyroxylic spirit.

II. ACIDUM ACETICUM GLACIALE (U. S. P.). Glacial acetic acid; Radical vinegar.

Preparation.—Pure sodium acetate (13 ½ parts), in crystals, is carefully heated until the water of crystallization is completely driven off and the salt fused. The residue (nearly 8 ¼ parts by weight) is then reduced to a coarse powder and transferred to a retort. The retort is then carefully warmed in a sand-bath; and to the contained salt is added from 9 ½ to 10 parts by weight of strong sulphuric acid and intimately mixed. It is then distilled. The product, though containing some water, is glacial acetic acid. It may be obtained nearly free from water by distilling a portion and then pouring off the liquid, and finishing the distillation by repeating the operation.

Description.—Glacial acetic acid is the strongest preparation of acetic acid, and is so named on account of its ice-like appearance when crystallized. According to both the British and United States Pharmacopoeias, it should contain at least 99 per cent of absolute acid. Below 15.5° C. (60° F.) it forms flat, colorless, ice-like, rhombic crystals. If heated above this point it changes to a syrupy, colorless liquid, which may again be cooled to 10° C. (50° F.), and remains fluid unless a crystal be dropped into it, when it again solidifies. Acetic acid of any form should not be kept in bottles stopped with rubber, as it is liable to be contaminated by substances used in the vulcanizing of the rubber. Glacial acetic acid dissolves camphor, oils, both volatile and fixed, gum-resins, resins, albumen, and fibrin. In contact with the skin it destroys the epidermal tissues and even produces vesication. It is thus described by the U.S.P.: "Nearly or quite absolute acetic acid. A clear, colorless liquid, of a strong, vinegar-like odor, and a very pungent, purely acid taste. When the acid is cooled to a temperature as near as possible to 15° C. (59° F.), but yet in a liquid form, its specific gravity should not be higher than 1.058, corresponding to at least 99 per cent of absolute acid. At a temperature somewhat below 15° C. (59° F.), the acid becomes a crystalline solid. When crystallized by cold it becomes liquid again at about 15° C. (59° F.). At 117° to 118° C. (242.6° to 244.4° F.) it boils, evolving inflammable vapors. Glacial acetic acid corresponds in properties to acetic acid (see Acidum Aceticum), and should respond to the same tests of purity; but the tint produced by the addition of 2 drops of decinormal potassium permanganate V.S. to 2 Cc. of the acid diluted with 10 Cc. of water, contained in a clean, glass-stoppered vial, should not be changed to brown within two hours. To neutralize 3 Gm. of Glacial acetic acid should require not less than 49.5 Cc. of potassium hydrate V.S. (each cubic centimeter corresponding to 2 per cent of the absolute acid), phenolphtalein being used as indicator"—(U. S. P.).

III. ACIDUM ACETICUM (U. S. P.). Acetic acid.

Preparation.—The acetic acid of commerce is derived from the action of sulphuric acid on pure sodium acetate, and indirectly from pyroligneous acid. Even fractional distillations of the latter acid, as pursued in obtaining rectified wood vinegar, will not completely purify it and chemical means must be resorted to in order to obtain pure acetic acid. Several methods are in vogue for this purpose. By the older method the crude pyroligneous acid was neutralized with milk of lime and the wood naphtha then distilled off; the remaining solution yielded upon evaporation to dryness a tarry residue of brown acetate of lime, containing only 68 to 69 per cent of pure acetate. By a later method, it is preferred to add milk of lime to the rectified wood vinegar (purified pyroligneous acid) and thus obtain by evaporation to dryness, a gray acetate of lime of much greater purity, containing 85 to 86 per cent of pure acetate.

Free acetic acid is then liberated from the acetates by distilling them with sulphuric acid, or preferably with hydrochloric acid which is added in a quantity just sufficient to convert the calcium into CaCl2. It is also preferred to convert the calcium acetate into sodium acetate before distilling with acid, by the double decomposition of calcium acetate and sodium sulphate. The sodium acetate is then carefully purified by evaporation and repeated recrystallization, finally being fused in an iron vessel, stirred until dry, and gently heated to incipient carbonization, thus ridding it of remaining empyreumatic impurities, and pure sodium acetate results. By distilling this salt with about 35 per cent of its weight of sulphuric acid the acetic acid of commerce is obtained. The remaining smoky flavor and odor may be removed by passing it through animal charcoal, or distilling it with bichromate of potassium.

Description.—Acetic acid of commerce is a solution of pure acetic acid in water, and according to the United States Pharmacopoeia should contain 36 per cent of the stronger acid. It should be clear, colorless, free from empyreuma, of a pure, intense sour taste, and of an acetous odor. Its specific gravity is about 1.048 at 15° C. (59° F.) (U. S. P.). It mixes freely with water and alcohol in all proportions, and should volatilize completely without residue (U. S. P.). Acetic acid gives rise to a line of salts known as the acetates. The salts (most of them are soluble) in solution, upon the addition of a solution of ferric salts, acquire a dark brown-red color, which vanishes when hydrochloric acid is added. If acetic acid be neutralized (or even left slightly acid) with solution of ammonium hydroxide and treated with the pharmacopoeial test solution of ferric chloride, a blood-red color results which may be discharged by adding to it an excess of sulphuric acid. The quality and odor of acetic acid are developed with age. According to Dr. E. R. Squibb, a sample of the freshly distilled acetic acid tested by the odor would not be recognized as the same substance a few months later. Many methods have been given for determining the amount of absolute acid in a given sample of the official preparation. The following test is accurate and will answer all practical purposes. Treat 200 grains of the acetic acid with a weighed excess of dry, pure calcium carbonate. Wash from it the calcium acetate thus formed, dry the residue, and weigh the insoluble carbonate. Multiply the loss in grains by three-fifths which will give the percentage strength of absolute acid.

Tests.—"When the acid is slightly supersaturated with ammonia, the liquid should not have a bluish tint (absence of copper), nor should any residue be left after evaporating the alkaline liquid on the water-bath (absence of other fixed impurities). Acetic acid diluted with 20 volumes of water should neither become colored nor yield a precipitate with hydrogen sulphide T.S. (absence of lead, copper, etc.). Acetic acid diluted with 10 volumes of water should not yield a precipitate or turbidity with barium chloride T.S. (absence of sulphuric acid), or with silver nitrate T.S. (absence of hydrochloric acid). If a portion of the acid be just neutralized by ammonia, then mixed with some silver nitrate T.S., and warmed, the liquid should not turn dark-colored or deposit a dark-colored precipitate (absence of formic or sulphurous acid). When the acid is slightly supersaturated by sodium or potassium hydrate T.S., the liquid should not have a smoky odor or taste. And if 5 drops of decinormal potassium permanganate V.S. be mixed with 2 Cc. of the acid previously diluted with 10 Cc. of water, and contained in a clean, glass-stoppered vial, the pink tint should not change at once to brown, but should change only gradually, and not become entirely brown, or free from pinkish-brown, in less than half a minute (limit of empyreumatic substances). To neutralize 6 Gm. of acetic acid should require 36 Cc. of normal potassium hydrate V.S. (each Cc. corresponding to 1 per cent of the absolute acid), phenolphtalein being used as indicator" (U. S. P.). (See also Acetum Destillatum).

IV. ACIDUM ACETICUM DILUTUM (U. S. P.).—Diluted acetic acid.

Preparation: According to the British Pharmacopoeia, this form contains acetic acid 1 part, distilled water 7 parts, by measure. These proportions are to be preferred to those of the U. S. P., which directs a mixture of 100 parts of acetic acid to 500 parts of distilled water. The former preparation is about the strength of ordinary vinegar, and is to be preferred on that account inasmuch as it can be conveniently used in preparations where vinegar is directed, making a much finer preparation.

Description: According to the United States Pharmacopoeia, "Diluted acetic acid contains 6 per cent, by weight, of absolute acetic acid. Specific gravity, about 1.008 at 15° C. (59° F.). it corresponds, in properties to acetic acid (see Acidum Aceticum), and should respond to the same tests of purity. To neutralize 24 Gm. of diluted acetic acid should require 24 Cc. of potassium hydrate V.S. (each Cc. corresponding to 0.25 per cent of the absolute acid), phenolphtalein being used as indicator"—(U. S. P.).

Action, Medical Uses, and Dosage.—Applied to the skin glacial acetic acid will cause vesication followed by a painful sore. Acetic acid acts upon the integument as a mild irritant unless its contact be prolonged, when it blisters and finally destroys the epidermis. Mucous tissues are turned first white and then brown by it. If a large dose be swallowed violent, burning, gastric pain with vomiting and diarrhoea results. Cases of fatal perforation have occurred from accidental swallowing of this acid. It reduces temperature and slows the pulse when taken in diluted form. Its continued use produces changes in the blood corpuscles, by its action on the alkalinity of the blood. When it kills it does so by arresting the heart's action. Convulsions and coma have preceded death when glacial acetic acid has been swallowed, and when not fatal it has produced gastro-enteritis. In cases of poisoning by this acid weak alkaline solutions should be immediately administered, followed by the use of milk and mucilaginous drinks. The stomach-pump should be employed to evacuate the stomach.

I. PYROLIGNEOUS ACID. Fish and meats, fresh or salted, immersed for a few seconds in crude pyroligneous acid, acquire a smoky taste, and are as well cured as by the usual method of smoking, besides being preserved from "skippers." Silliman found that if a quart of this acid be added to the pickling liquid when hams are packed in it, they would have as perfect a smoky flavor as if they had gone through the usual process of preparation by smoking. This acid is stimulant and antiseptic. The diluted acid may be used as a local application for arresting or preventing sloughing, for cleansing old or gangrenous sores, abscesses and burns, scalds, ringworms, tinea capitis, excoriated nipples, etc., and as a gargle in inflamed and ulcerated throat, and scarlatina maligna. Internally, in doses of from 10 to 80 drops, it is useful in all cases where an antiseptic is indicated. The pyroligneous tar forms a valuable irritating plaster.

II. GLACIAL ACETIC ACID. This acid attacks flesh and is too concentrated for internal use. It destroys the epidermis and may produce a painful sore. It may be used to destroy growths, such as warty excrescences, corns, and occasionally as a vesicant. This form of acid is one of our best agents for the cure of ringworm. The parts should be touched with a hair pencil dipped in the acid. Ulcers, papillomata, lupus, epithelioma and nasal polypi have been successfully treated with it. It is an excellent application in scald head, though care should be exercised in its use not to produce an ulcerated condition of the scalp. M. Ricord speaks highly of this acid as a local application to venereal ulcers in the primary stage, to be applied as freely as any other caustic, and repeated as often as the condition of the chancres may require. Under its influence the ulcer speedily assumes a healthy aspect and promptly heals. He believes that it neutralizes the venereal poison, and thus obviates all danger of constitutional symptoms.

III. ACETIC ACID. Acetic Acid is well known for its property of preserving vegetable substances, such as pickles, etc. It is antiseptic, refrigerant, astringent, and excitant. Its volatility renders it efficient for inhalation in cases of fainting, suffocation, headache and hoarseness. A small quantity of acetic acid poured into the vessel containing the feces of typhoid fever patients, as well as those suffering from tubercular consumption and tubercular diarrhoea, will destroy the offensive odor arising therefrom. Acetic acid is claimed to be the only agent that will "liquefy and disorganize cancer cells." For this purpose a dilution of acetic acid has been applied to epitheliomata for the purpose of destroying the nature of the growths. This must be done, however, before the axillary or other glands have become involved. Fair success has attended this practice which is to be pursued only when the patient refuses to have the cancerous mass removed. Injected hypodermatically into nasal polypi, pure acetic acid has been found to quickly cause the tumors to shrivel and drop away. Should they suppurate and become offensive, deodorants, such as asepsin or borax, may follow its use to overcome the stench arising therefrom. Acetic acid 1 part, distilled water 2 parts, has been of service as an injection in gonorrhoea.

IV. DILUTED ACETIC ACID. Diluted acetic acid is always an efficient antidote for poisoning by the caustic alkalies. If this be not at hand diluted vinegar (which is an impure acetic acid) is always to be obtained and should be employed in such cases. This acid applied to an urticarious eruption will usually allay the disagreeable itching. It checks moderate hemorrhages, consequently it may be given in hematemesis, and applied to superficial wounds and in the nose for the relief of epistaxis. It may be applied to ringworm when it is not desirable to employ the stronger acid. Used as a lotion it will prevent the occurrence of bed sores, and added to the bath will frequently be beneficial in reducing temperature in febrile conditions. Vinegar may be employed for the same purposes. Diluted acetic acid has been given to cheek the colliquative sweating of phthisical patients. Acetic acid is not often used internally, but when so used this form is selected and the indications below given are the guides to its use.

Specific Indications and Uses.—Deep redness of tongue and mucous surfaces.

Preparations.—CAMPHORATED ACETIC ACID. Half an ounce of camphor triturated with a little alcohol to reduce it to powder, and then dissolved in 6 fluid ounces of this acid, forms the Camphorated Acetic Acid of the Dublin Pharmacopoeiaup the nostrils; as it is extremely volatile and , which is a pungent stimulant when snuffed corrodes nearly all common metals except gold, it should be kept in glass vials, with ground-glass stoppers. Henry's aromatic vinegar is merely an acetic solution of camphor, oil of cloves, lavender, and rosemary.

Related Acids.—ACIDUM TRICHLORACETICUM, Trichloracetic acid. (CCl3COOH). When chlorine acts upon acetic acid chloracetic acid in three modifications is formed accordingly as the hydrogen atoms are replaced with one, two or three atoms of chlorine, resulting respectively in mono-chloracetic, di-chloracetic, and trichloracetic acids, the latter of which is used in medicine. It may also be prepared by acting upon anhydrous chloral with fuming nitric acid—a process of oxidation. It forms colorless, very hygroscopic, rhombic crystals having a faintly pungent smell, and strongly reddening litmus. At 55° C. (131° F.) it fuses; at 195° C. (463° F.) it boils. Chloroform (CHCl3) and carbon dioxide (CO2) are formed when it is decomposed by boiling with an excess of sodium carbonate. It has been used from full strength to 50 per cent solutions as a cauterant and is likewise used in urinary analysis as a test-reagent for albumen (Coblentz). As a cauterant it is said to cause less pain than the commonly employed caustics, and the pain (in mucous tissues) way be wholly obtunded by the previous application of cocaine. In its action it somewhat resembles nitric acid, penetrating deeply without much inflaming the surrounding tissues, and the small dry, and smooth, white eschar soon falls off, exhibiting granulations, and the sore very quickly heals. Very little contraction takes place and the scar is inconsiderable. It has been employed for the removal of papillomata, lupus, vascular naevi, warts, condylomata, and various neoplasms. To a limited extent it has been used to cauterize the mucous surface after the removal of exuberant growths of the middle ear" (Foltz). A 20 per cent solution has been affirmed (Lanz) to cure obstinate gleet by cauterization.

King's American Dispensatory, 1898, was written by Harvey Wickes Felter, M.D., and John Uri Lloyd, Phr. M., Ph. D.