Picric Acid

PICRIC ACID (2,4,6-trinitrophenol), (OH)C₆H₂(NO₂)₃ (from Greek picros - bitter), brilliant pale yellow crystalline flakes or prismatic crystals, sparingly soluble in cold water (1.225 parts in 100 parts of water at 20°), readily soluble in boiling water, alcohol, and ether. Melting point 122.5, specific gravity 1.67-1.69. Formed by boiling various animal and vegetable substances with concentrated nitric acid (silk, leather, wool, resin, aniline, indigo); P. acid is the end product of the nitration of phenol. Aqueous solutions are bitter and have an intense yellow color. Potassium cyanide can serve as a reagent for P. acid (formation of isopurpuric acid). With bases, P. acid gives salts - picrates. Many picrates of organic bases crystallize well; P. acid also forms well-crystallizing molecular compounds with aromatic hydrocarbons, which can be used for their isolation; many picrates are highly explosive and have been used in explosive technology since the 1860s. P. acid is the oldest artificial dye for wool and silk. It is used to stain cytoplasm, hair, and the horny layers of the epidermis. The oldest therapeutic agent against malaria (now experimentally rejected). It was recommended as an analgesic and keratoplastic agent (in a 1% solution), as an anthelmintic. In ophthalmology, it is used for the treatment of tumors. The most recent area of application - internally for pellagra. In England, a 5% solution is used as an antiseptic instead of iodine. Poisonous to bacteria, plants, and animals. For poisoning with P. acid, see Poisoning. Sometimes used by recruits to simulate jaundice. (Discovery of P. acid in urine - see Urine.) Serves as a falsifier in brewing. A component of Spengler's reagent, Muh's reagent (see Sputum), Esbach's reagent, reagent for creatinine, reagent for precipitating proteins. P. acid and ammonium picrate are used in histological technique as fixatives for the vital staining of nerve elements with methylene blue (V. G. Smirnov, A. Dogel, V. Nikolaev).

N. Tolachevskaya. Discovery in judicial cases and in professional poisonings. No fatal cases from P. acid poisoning have been observed. The object of research for P. acid and for the product of its partial reduction - lycraminic acid [C₆H₂(NO₂)₂(NH₂)OH] is urine, which is colored bright red in the presence of picraminic acid. The skin of poisoned persons has a yellow color with an orange tint. To detect picric and picraminic acids, the urine is strongly acidified with dilute sulfuric acid and repeatedly extracted in a separatory funnel with small portions of ether. In the first portions of extraction, picraminic acid predominates, in the last - P. acid. This makes it possible to approximately separate them. From the obtained extract, the acids under investigation are transferred to an aqueous solution by shaking with a dilute solution of caustic soda. The aqueous solution is separated, repeatedly extracted with ether to remove foreign substances. Again acidified, extracted with ether. The ether is evaporated, the residue is dissolved in water, and the following reactions are performed with the solution: 1) heated with woolen or silk threads. The threads are stained by P. acid to a bright yellow color, by picraminic acid to an orange color; 2) when a yellow solution of P. acid is heated with glucose and soda, a red-orange color of picraminic acid appears; 3) to a portion of the solution of picric (and picraminic) acid, hydrochloric acid and zinc dust are added. The acids under investigation are reduced to triaminophenol. When shaken with air, a blue coloration appears due to oxidation. This oxidation is more conveniently caused by hydrogen peroxide with slight alkalization of the solution with aqueous ammonia. To detect P. acid dust in the air, the latter is washed by passing it through bottles with water. The presence of P. acid will be indicated by the yellowing of the water. Reactions for P. acid are performed with the solution, and colorimetric quantitative determination is made by comparison with standard solutions of P. acid. A. Stepanov. Professional poisonings with picric acid. Potassium and ammonium salts of it are explosive substances, and therefore P. acid finds wide application in the military industry - it is a component of melinite, lyddite, shimose, etc.; further, it is used as a dye and for tanning wood. P. acid is obtained from phenol by its nitration. Production processes: heating phenol with sulfuric acid, cooling, draining water; treating the resulting phenolsulfonic acid with nitric acid, after cooling, brilliant yellow crystals of P. acid precipitate; they are centrifuged, washed, and crystallized. Older authors assumed that P. acid poses a great danger to workers dealing with it, as laboratory observations and accidental acute poisonings gave a severe picture: severe pain in the stomach region, nephritis, strangury, anuria, irritation of the central nervous system, methemoglobin formation, etc. More recent observations (Koelsch, Curschmann), however, did not confirm these assumptions: professional poisonings with P. acid are rarely observed and are almost never accompanied by serious symptoms. Most often, local processes develop - inflammatory lesions of the skin, irritation of the conjunctiva and nasal mucosa; dust that gets into the mouth causes a very unpleasant bitter taste and loss of appetite; further, for P. acid, a greenish-yellow coloration of hair and a yellow coloration of uncovered parts of the skin are characteristic; in individual cases (increased sensitivity, uncleanliness), more serious general phenomena, eczema, furunculosis, were observed. Observations by Russian authors also confirmed that P. acid, while causing lesions of some organs, still does not cause serious poisoning phenomena: thus, Matushevich, when examining 20 people, found in all the aforementioned yellow coloration of the skin, in 3 people skin rashes, in 17 people catarrhs of the upper respiratory tract, in 12 people reduced acidity of gastric juice; all of them complained of bitterness in the mouth, poor appetite, heartburn, nausea, dry cough. Katin-Yartsev, when examining 7 workers, found in all of them hypertrophic catarrh of the nose, shortening of air conductivity on the basis of the pathological condition of the sound-conducting apparatus (blowing gave improvement). Prevention - complete hermetization of processes (boiling, sifting, weighing, filling, etc.) with the aim of preventing the release of dust and vapors.