Nitro Compounds

Nitro compounds are characterized by the presence of a NO₂ group attached to a carbon atom; for example CH₃-NO₂, whereas in esters of nitrous acid, which are isomeric with nitro compounds, N is connected to carbon through oxygen, for example CH₃-O-NO. Both aliphatic and cyclic nitro compounds are known. Aliphatic nitro compounds are obtained 1) by the action of HNO₃ on saturated hydrocarbons: C₆H₁₄ + NO₂.OH = C₆H₁₃.NO₂ + H₂O; 2) by the action of AgNO₂ on halogen derivatives of saturated hydrocarbons: C₂H₅J + AgNO₂ = C₂H₅NO₂ + AgJ; 3) by the action of KNO₂ on esters of sulfuric acid: (CH₃O)₂SO₂ + KNO₂ = CH₃NO₂ + CH₃O-. Aliphatic nitro compounds are neutral substances, the lower ones being liquids. Tertiary nitro compounds R₃C-NO₂ do not dissolve in alkalis, while primary R-CH₂-NO₂ and secondary R₂CH-NO₂ nitro compounds dissolve, forming salt-like compounds; in this process, neutral nitro compounds isomerize into acidic isonitro compounds: CH₃-CH₂-NO₂ + NaOH = H₂O + CH₃-CH:NO-ONa (corresponding isonitro compound-CH₃-CH:NO-OH). Primary nitro compounds give nitrolic acids with HNO₂, R-C:(OH)(NO₂); secondary ones give pseudonitroles, R₂:C(NO₂).NO; tertiary ones do not react.--Upon reduction, nitro compounds yield amines (see): CH₃-NO₂ + 3H₂ = CH₃-NH₂ + 2H₂O. Among aliphatic nitro compounds, chloropicrin, CCl₃-NO₂, has the greatest practical importance, used as a chemical warfare agent. Among cyclic nitro compounds, those of the aromatic series are most important. Nitro derivatives of aromatic hydrocarbons with a NO₂ group in the nucleus are obtained by the action of HNO₃ (mixed with H₂SO₄ as a dehydrating agent) on aromatic hydrocarbons (nitration reaction), for example C₆H₆ + NO₂.OH = C₆H₅-NO₂ + H₂O. Mononitro derivatives of aromatic hydrocarbons are liquids or solids, usually with a bitter almond odor, and are insoluble in water. Di- and trinitro compounds are yellow, crystalline, water-insoluble substances that are explosive. Nitro compounds are more or less toxic. The most important property of aromatic nitro compounds is their ability to give a series of successive reduction products, for example C₆H₅-NO₂ (nitrobenzene) → C₆H₅-NO (nitrosobenzene) → C₆H₅-NHOH (phenylhydroxylamine) → C₆H₅-N:N-C₆H₅ (azobenzene) → C₆H₅-NH-NH-C₆H₅ (hydrazobenzene) → C₆H₅-NH₂ (aminobenzene, or aniline). The production of amino derivatives by reduction of nitro derivatives is particularly important technically: C₆H₅-NO₂ + 3H₂ = C₆H₅-NH₂ + 2H₂O (see Aniline). For this purpose, very large quantities of nitrobenzene (see) and o- and p-nitrotoluenes (boiling point 218° and 238°) are prepared. Trinitrotoluene, or TNT C₆H₂(NO₂)₃-CH₃ (melting point 92°) is of great importance in military chemistry as one of the most important high explosives for filling artillery shells. Nitroanilines, for example p-C₆H₄(NH₂)-NO₂, are used in the manufacture of azo dyes. The most important representatives of nitrophenols are p-nitrophenol C₆H₄(NO₂)-OH, which is among other things used for the preparation of phenacetin and other medicinal substances, and picric acid (see) C₆H₂(NO₂)₃-OH.

I. Yaichnikov. Aromatic nitro compounds (as industrial poisons). Of the large number of nitro derivatives of benzene (see), the following substances have practical importance: nitro- and dinitrobenzene, nitro- and dinitrochlorobenzene, dinitro- and trinitrotoluene, trinitrophenol (picric acid), as well as dinitro- and tetranitronaphthalene, trinitroanisole, etc. In the chemical industry and in the production of explosives, these substances play an extremely important role.- Nitrobenzene, an oily yellow liquid with a bitter almond odor, is the starting product for obtaining aniline (see). Dinitrobenzene (a solid substance) serves as a raw material in the chemical industry and is used for the production of the common explosive roburite; dinitrochlorobenzene is used for the production of sulfur dyes and explosives; trinitrotoluene is a very powerful, widely used military explosive, as are many other polynitro compounds.- Various compounds of benzene and its homologs, in terms of their effect on the human body, routes of penetration, and symptoms of poisoning, generally possess the same properties; the difference lies only in the degree of toxic effect. An increase in the number of nitro groups in a substance generally increases its toxicity; substances in which the groups replacing hydrogen atoms in the compound are in the para position are more toxic than when located in the ortho or meta position. The presence of chlorine in nitro compounds, in addition to the usual clinical symptoms of nitro compound poisoning, also causes significant irritation of the skin and mucous membranes and affects the cardiovascular system, causing a labile state of it for a long time (Kharchenko and Leites; see Dinitrochlorobenzene). Trinitroanisole has a particularly irritating effect on the skin; trinitrophenol (picric acid) stains the skin and hair yellow or yellowish-green; in other cases it causes skin lesions, etc. Predisposition to poisoning by nitro compounds, as with other benzene derivatives, varies greatly individually; it is higher in young people, as well as in older persons, and also in women, especially during puberty, menstruation, pregnancy, and lactation. Persons of weak constitution, with poor nutrition, suffering from organic diseases (especially of the circulatory and excretory systems) and metabolic diseases, convalescents, and especially alcoholics are poisoned much more often and endure the illness more severely. Damage and diseases of the skin, as well as increased sweating, facilitate the penetration of the poison through the skin and then its general resorptive effect. These poisons penetrate the body even through the skin, and not only through damaged or diseased skin, but also through completely healthy skin (for example, most of the acute poisonings with nitrobenzene, dinitrochlorobenzene, etc. that occurred in the USSR occurred precisely by this route); in the form of vapors or dust, they also penetrate through the respiratory or digestive tract. They are excreted from the body mainly with urine in the form of various transformation products (for example, para-aminophenol). For the clinical picture of poisonings, treatment and prevention, see Nitrobenzene, Dinitrobenzene, Dinitrochlorobenzene.

NITRO compounds. Poisoning by nitro compounds and their derivatives (nitrobenzene, dinitrobenzene, dinitrochlorobenzene, trinitrotoluene, etc.) occurs in the chemical industry, during the production and use of explosives, and in agriculture. The main route of entry into the body is through the skin (even intact), less often through the respiratory tract. The clinical picture is characterized by cyanosis, headache, dizziness, nausea, vomiting, pain in the abdomen, sometimes hematuria. In severe cases, collapse, convulsions, and coma develop. Treatment: removal of the poison from the body, symptomatic therapy. Prevention: compliance with safety regulations when working with nitro compounds, use of protective equipment.