Nitro compounds: preparation and properties
Compounds formed when a hydrogen atom of a hydrocarbon is replaced by the nitro group –NO₂ are nitro compounds (R–NO₂). The rational name is the hydrocarbon name plus “nitro”: nitromethane CH₃NO₂, nitroethane C₂H₅NO₂; in systematic names the nitro group is a numbered substituent: 1-nitropropane, 2-nitropropane, 2-methyl-2-nitropropane. Nitro compounds are interclass isomers of amino acids: nitroethane C₂H₅NO₂ and glycine H₂N–CH₂–COOH. Preparation is nitration: heating alkanes with dilute HNO₃ (about 140 °C), and arenes with a mixture of concentrated HNO₃ and H₂SO₄: C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O. Nitrobenzene is a pale-yellow oily poisonous liquid with a bitter-almond smell. The most important property is reduction: a nitro compound becomes an amine. N. N. Zinin (1842) obtained aniline from nitrobenzene; today H₂ with a catalyst or a metal with acid is used: C₆H₅NO₂ + 3H₂ → C₆H₅NH₂ + 2H₂O. Nitro compounds are intermediates in the synthesis of dyes, drugs and solvents; some polynitro compounds (trinitrotoluene, picric acid) are explosive and only specialists handle them.
Table: nitromethane, nitroethane, nitrobenzene — formula, molar mass, use. Only general information about explosives is read; nothing is done about making or using them.