Benzoic acid

“ By the action of sodium amalgam on an aqueous solution of the acid, benzyl alcohol, tetrahydrobenzoic acid and hexahydrobenzoic acid are formed. The salts of benzoic acid are known as the benzoates and are mostly soluble in water. They are readily decomposed by mineral acids with the production of benzoic acid, and on addition of ferric chloride to their neutral solutions give a reddish-brown precipitate of ferric benzoate. ”

“ Bitter almond oil, which by oxidation yields benzoic acid, is wanting in benzoin. Very little volatile oil is in fact to be got; half a pound of the best Penang benzoin yielded us by distillation with water only a few drops of an extremely fragrant oil (styrol?) .
Ferric chloride imparts to an alcoholic solution of benzoin a dark brownish green, which is not acquired under the same circumstances by the aqueous decoction of the powdered resin. Benzoin dissolves in cold oil of vitriol, forming a solution of splendid carmine hue, from which water separates crystals of benzoic acid. ”

“ If it is found to contain sufficient benzoic acid to react with a considerable proportion of the sodium alcoholate, a poor yield of ester will be obtained. Less than 1 per cent of benzoic acid will not interfere seriously with the yields obtained, but the presence of larger quantities of acid will be found to be detrimental and must be removed by washing the benzaldehyde with a sodium carbonate solution and redistilling with the precautions necessary to prevent too free an access of air to the distillate. ”

“ Benzoic acid is perfectly soluble in hot grease. Half an ounce of benzoic acid being dissolved in half a pint of hot olive or almond oil, deposits on cooling beautiful acicular crystals, similar to the crystals that effloresce from vanilla beans; a portion of the acid, however, remains dissolved in the oil at the ordinary temperature, and imparts to it the peculiar aroma of benzoin ”

“ Benzoic acid crystallizes in glistening leaflets (from water) which melt at 121.4° C. and boil at 249.2° C. (H. Kopp) . Its specific heat is 0.1946. It sublimes readily and is volatile in steam. It is readily soluble in hot water and the ordinary organic solvents, but is only slightly soluble in cold water. When heated with lime, it is decomposed, benzene being formed; if its vapours are passed over heated zinc dust, it is converted into benzaldehyde (A. Baeyer, Ann. 1866, 140, p. 296) . Distillation of its calcium salt gives benzophenone (q.v.) ”

“ The greater part of the oil floats over the surface of the acid, and, if the former be free {209} from adulteration, no change of color takes place within several hours in either; but after the lapse of three or four days crystals of benzoic acid will begin to be formed from the oxidation of the hyduret of benzoyle by the nitric acid, and these will increase in quantity until the whole becomes a solid mass of crystals, which will gradually assume a bright emerald green color. This reaction is very char­ac­ter­is­tic. ”

“ The heat volatilizes the benzoic acid, the above-mentioned essential oil, and some tarry substances of a brown color. The latter are arrested by the filter paper, while the benzoic acid is deposited on the cone and in the tube, in the form of delicate glossy needles which are very fragrant owing to the essential oil. The largest yield of benzoic acid is obtained when the temperature is raised very gradually, until finally nothing remains in the copper boiler but a brown, almost carbonized mass of a blistered appearance. ”

“ Chlorine and nitric acid oxidize it to benzil; chromic acid mixture and potassium permanganate, to benzoic acid and benzaldehyde. On heating with zinc dust, desoxy-benzoin (C6H5CO·CH2·C6H5) is obtained; sodium amalgam converts it into hydrobenzoin; and fuming hydriodic acid at 130° C. gives dibenzyl (C6H5CH2·CH2·C6H5) . By fusion with alkali it is converted into benzil; and with an alcoholic solution of benzaldehyde in presence of ammonia it forms amarine (triphenyl dihydro-glyoxaline) . ”

“ When obtained by sublimation benzoic acid forms soft, light, feathery, white, flexible crystals, which are transparent or semi-transparent, with more or less of a mother-of-pearl lustre; when by slowly cooling its aqueous solution, or by precipitation from a solution of a benzoate, it forms either thin plates or scales, or a dazzling white crystalline powder. It is inodorous when cold, [153] but acquires a faint balsamic odour when gently warmed; fuses at about 212° Fahr., and begins to sublime freely at a temperature a little above it, but does not boil until heated to about 460° ”

“ When benzoic acid is prepared by any of the wet processes, it is free from the fragrant volatile oil which accompanies it when prepared by sublimation from the resin, and to which oil the acid of commerce owes its peculiar odor. ”

“ The classical investigation of Liebig and Friedrich Wohler on the radical of benzoic acid (“Über das Radikal der Benzoë-säure,” Ann. Chem., 1832, 3, p. 249) is to be regarded as a most important contribution to the radical theory, for it was shown that a radical containing the elements carbon, hydrogen and oxygen, which they named benzoyl (the termination yl coming from the Gr. ὔλη, matter) , formed the basis of benzaldehyde, benzoic acid, benzoyl chloride, benzoyl bromide and benzoyl sulphide, benzamide and benzoic ether. ”

“ Perhaps the final solution of the benzoic acid problem could be best obtained directly from the people at large. If they were to consume benzoic acid as knowingly as they consume, for example, sodic carbonate in soda biscuits, or caffeine and theobromine in coffee and tea, it would not require more than a decade or two before we should have a well-defined and well-founded public opinion on the subject, at least in the medical profession. ”

“ Similarly, the replacement of hydrogen by a water-residue, hydroxyl, gives rise to a phenol. The group of carbon, oxygen, and hydrogen atoms which confers the property of acidity upon an organic compound is a half-molecule of oxalic acid—it is known as the carboxyl group. Thus benzoic acid is the carboxyl-derivative of benzene, and the phthalic acid with which we are now concerned is a dicarboxyl-derivative of benzene. It is related to benzoic acid in the same way that diamidobenzene is related to aniline. ”

“ Benzoin is not manifestly acted on by bisulphide of carbon, but if kept in contact with it for a month or two, very large colourless crystals of benzoic acid make their appearance. Brought into a warm room, the crystals quickly dissolve, but are easily reproduced by exposure to cold.
Most pharmacopœias require not the inodorous acid obtained by a wet process, but that afforded by sublimation, which contains a small amount of fragrant empyreumatic products. The resin, when repeatedly subjected to sublimation, affords as much as 14 per cent. ”

“ Chemical Composition. Volatile oil, resin, mucilage, extractive, iron, and small portions of the carbonate of potass, lime and ammonia. It contains also, according to the analysis of Laugier, a small quantity of Benzoic acid. The Canadian variety is also stated by Laugier to contain benzoic acid both free and combined. Solubility. Its active matter is dissolved by alcohol, proof spirit, and partially by water; the tincture made with alcohol is the least nauseous, and the most efficacious; the spirit of ammonia is also an excellent menstruum, and in many cases improves its virtues. ”

“ Also from phthalic acid, C8H6O4, there may be obtained benzoic acid, C7H6O2, and carbonic anhydride, CO2, and as all the elements of phthalic acid enter into the composition of these substances, it follows that, although [311] they cannot re-form it by their direct action on each other (the reaction is not reversible) , still they form the direct products of its decomposition, and they occupy equal volumes. But benzoic acid, C7H6O2, is itself composed of benzene, C6H6, and carbonic anhydride, CO2, which also occupy equal volumes. ”

“ Then procure a small quantity of benzoic acid, which exists in the shape of snowy crystals. Elevate the bell-glass upon a little stage made of books or pieces of wood, so as to allow a spirit-lamp to be introduced underneath, and a little evaporating dish to be held above the flame by means of a ring of wire with suitable handle. Place the benzoic acid in the evaporating dish, over the flame, and presently the acid will ascend in vapor and fill the bell, which must not be quite closed at the top. ”

“ It may be decoloured by redissolving it in boiling water, and treating it with animal charcoal, or with a little chloride of lime along with some hydrochloric acid, and re-crystallising it.
Obs. Hippuric acid, when pure, forms long, slender, milk-white, square prisms; it is soluble in 400 parts of cold water; it also dissolves in hot alcohol. When strongly heated, it yields benzoic acid, benzoate of ammonia, and benzonitrile, with a coaly residue. ”

“ It fuses at a gentle heat and exhales white fumes, which, on condensation, are found to be benzoic acid contaminated with a little volatile oil. Alcohol dissolves the larger portion of it, ether much less, and the volatile and fixed oils only a little. It contains from 9% to 18, or (occasionally) nearly 20%, of benzoic acid, according to the quality. It burns with an agreeable odour. The resin and its alcoholic solution strike a bright red colour with oil of vitriol, and a green colour with chloride of iron. ”

“ The accomplishment of such an effect is in many instances the sole object of a pharmaceutical process. It is thus that we obtain pure Citric acid from the juice of the Lemon; Tartaric acid, from Cream of Tartar; Benzoic acid, from the resinous substance known by the name of Gum Benzoin; upon the same principle, the Muriatic and Nitric acids are elicited from the saline compounds in which they exist. Ammonia, in its pungent form, is developed from its inodorous Muriate ”

“ It suggests that even the small quantities of benzoic acid which we get with unadulterated food, or produce within ourselves, might be deleterious to health except for the saving hippuric acid forming process. And because that "factor of safety" is a large one with respect to the normal benzoic acid content of our food it does not follow that we can encroach on it with perfect impunity. What the effect of a general, regular encroachment on it would be cannot be determined by a few relatively short feeding experiments. ”

“ The oxidation of benzaldehyde to benzoic acid when exposed to air is not one of ordinary oxidation, for it has been observed in the case of many compounds that during such oxidation, as much oxygen is rendered “active” as is used up by the substance undergoing oxidation; thus if benzaldehyde is left for some time in contact with air, water and indigosulphonic acid, just as much oxygen is used up in oxidizing the indigo compound as in oxidizing the aldehyde. ”

“ As a medicine, its general effects resemble those of the other true balsams, and of benzoic acid.—Dose, 5 or 6 to 20, or even 30 gr., in powder, and usually in combination with some other remedy; chiefly in chronic pulmonary and bronchial affections, when occurring in torpid habits, and unaccompanied by inflammatory symptoms or gastric irritation. Also as a fumigation in the same diseases, hooping-cough, &c. Like benzoic acid, it is used to prevent rancidity in ointments, pomades, and other fatty preparations. ”

“ When heated, these white specks rise as a smoke, which is easily condensed upon paper. The material thus separated from the benzoin is called flowers of benzoin in commerce, and by chemists is termed benzoic acid. It has all, or nearly all, the odor of the resin from which it is derived.
The extract, or tincture of benzoin, forms a good basis for a bouquet. [B] Like balsam of Tolu, it gives permanence and body to a perfume made with an essential oil in spirit. ”

“ Neutralize with sodium hydrate and evaporate to dryness or to a small volume. After treating with 3 cc. of concentrated sulfuric acid, heat till white fumes appear. Add 4 or 5 crystals of potassium nitrate and continue heating until the solution is colorless or nearly so. When cool dilute with water, add an excess of ammonia, and place in a narrow vessel like a test tube. Add one or two drops of ammonium sulfid carefully so that the liquids do not mix. If the surface of [11] the liquid immediately becomes red, benzoic acid is present. ”

“ E. Mitscherlich prepared it in 1834 by distilling benzoic acid with lime; and in 1845 Hofmann discovered it in coal-tar. It was named “benzin” or “benzine” by Mitscherlich in 1833, but in the following year Liebig proposed “benzol” (the termination ol being suggested by the Lat. oleum, oil) ; the form “benzene” was due to A.W. Hofmann. The word “benzine” is sometimes used in commerce for the coal-tar product, but also for the light petroleum better known as petroleum-benzine ”

“ The first of the above-named substances, benzol, was discovered by Faraday, in 1825, in liquid produced by strongly compressing gas obtained from oil. He called it bicarburet of hydrogen; but afterwards another chemist, having procured the same body by distilling benzoic acid with lime, termed it benzine. It readily dissolves fats and oils; and is used domestically for removing grease-spots, cleaning gloves, &c., and in the arts as a solvent of india-rubber and gutta-percha. It is a very limpid, colourless liquid, very volatile, and, when pure, is of a peculiar but not disagreeable odour. ”