Benzoic Acid

BENZOIC ACID, Acidum benzoicum, C₆H₅COOH, used for medical purposes, is obtained either by the sublimation of benzoin resin or synthetically and appears as needle-flat crystals with a melting point of 120-121.5°, soluble in 450 parts of water, easily soluble in alcohol (3 parts), ether, and glycerin; volatile with water vapor. Benzoic acid has a strongly irritating local effect; when large doses are taken internally, vomiting, stomach pain, and diarrhea may appear, and upon inhalation of a strongly concentrated solution, coughing. Being chemically close to salicylic acid, it possesses its properties—antiseptic and antipyretic—but significantly less pronounced. Benzoic acid is rapidly absorbed by the intestines, and then the greater part of it is excreted in the urine in the form of hippuric acid (C₆H₅CONHCH₂COOH), while the remainder is partly destroyed in the organism and partly excreted in unchanged form by the salivary, bronchial, and sweat glands. Benzoic acid is used mainly as an expectorant, which is explained by the fact that benzoic acid, partly being excreted on the mucous membrane of the respiratory tract, exerts a weakly irritating effect on it. In addition, benzoic acid increases urine acidity and prevents abnormal urine fermentation in the bladder. Benzoic acid also exerts a favorable effect on the urinary tract in pyelitis and cystitis (Robin). Benzoic acid is prescribed in a mixture or pills at 0.05-0.25 per dose, several times a day.—Sodium benzoate, C₆H₅COONa · H₂O, Natrium benzoicum, is easily soluble in water (1 : 2 parts), less easily in alcohol (1 : 24 parts) and glycerin (1 : 9 parts), possesses a weaker irritating effect than benzoic acid, is prescribed in the same cases as the latter, and in addition—for gout at 0.3-1.0 per dose, up to 10.0 per day (in powders, mixtures, pills); for local action on the respiratory tract (in the form of inhalations), a 5% solution is used. In other salts, such as lithium, mercury, and bismuth benzoate, the pharmacological action belongs not to benzoic acid, but to the metal. In the form of benzoin resin, benzoic acid is part of various mixtures prescribed as an expectorant.

M. Likhachev. Detection of benzoic acid in forensic cases. To establish the presence of benzoic acid during forensic examinations as an illicit preservative for food products, particularly beverages (e.g., fruit waters), the object of investigation, after adding diluted sulfuric acid, is extracted with a mixture of ethyl and petroleum ether; the extract is evaporated at room temperature, the residue is placed in a small crucible covered with a watch glass, and carefully heated: a characteristic needle-like sublimate is obtained (melting point 120-121°). The residue is converted into salicylic acid; mixed with 1 cubic centimeter of water, 2 drops of hydrogen peroxide and 1 drop of ferric chloride solution are added. Upon standing (3-6 hours), a violet or red-violet coloration appears.