In organic chemistry, nitro compounds are organic compounds that contain one or more nitrofunctional groups (−NO2). The nitro group is one of the most common explosophores (functional group that makes a compound explosive) used globally. The nitro group is also strongly electron-withdrawing. Because of this property, C−H bonds alpha (adjacent) to the nitro group can be acidic. For similar reasons, the presence of nitro groups in aromatic compounds retards electrophilic aromatic substitution but facilitates nucleophilic aromatic substitution. Nitro groups are rarely found in nature. They are almost invariably produced by nitration reactions starting with nitric acid.[1]
Synthesis
Preparation of aromatic nitro compounds
Aromatic nitro compounds are typically synthesized by nitration. Nitration is achieved using a mixture of nitric acid and sulfuric acid, which produce the nitronium ion (NO+2), which is the electrophile:
+
H+
The nitration product produced on the largest scale, by far, is nitrobenzene. Many explosives are produced by nitration including trinitrophenol (picric acid), trinitrotoluene (TNT), and trinitroresorcinol (styphnic acid).[3]Another but more specialized method for making aryl–NO2 group starts from halogenated phenols, is the Zinke nitration.
Preparation of aliphatic nitro compounds
Aliphatic nitro compounds can be synthesized by various methods; notable examples include:
Despite the occasional use in pharmaceuticals, the nitro group is associated with mutagenicity and genotoxicity and therefore is often regarded as a liability in the drug discovery process.[20]
Nitronates are also key intermediates in the Nef reaction: when exposed to acids or oxidants, a nitronate hydrolyzes to a carbonyl and azanone.[26]
Grignard reagents combine with nitro compounds to give a nitrone; but a Grignard reagent with an α hydrogen will then add again to the nitrone to give a hydroxylamine salt.[27]
Many flavin-dependent enzymes are capable of oxidizing aliphatic nitro compounds to less-toxic aldehydes and ketones. Nitroalkane oxidase and 3-nitropropionate oxidase oxidize aliphatic nitro compounds exclusively, whereas other enzymes such as glucose oxidase have other physiological substrates.[28]
Explosions
Explosive decomposition of organo nitro compounds are redox reactions, wherein both the oxidant (nitro group) and the fuel (hydrocarbon substituent) are bound within the same molecule. The explosion process generates heat by forming highly stable products including molecular nitrogen (N2), carbon dioxide, and water. The explosive power of this redox reaction is enhanced because these stable products are gases at mild temperatures. Many contact explosives contain the nitro group.
^Henry Feuer, ed. (1970). Nitro and Nitroso Groups: Part 2, Volume 2. PATAI'S Chemistry of Functional Groups. Vol. 2. John Wiley & Sons Ltd. doi:10.1002/9780470771174. ISBN 978-0-470-77117-4.Saul Patai, ed. (1982). Nitro and Nitroso Groups: Supplement F: Part 2, Volume 2. PATAI'S Chemistry of Functional Groups. John Wiley & Sons Ltd. doi:10.1002/9780470771679. ISBN 978-0-470-77167-9.Saul Patai, ed. (1982). Amino, Nitroso and Nitro Compounds and Their Derivatives: Supplement F: Part 1, Volume 1. PATAI'S Chemistry of Functional Groups. John Wiley & Sons Ltd. doi:10.1002/9780470771662. ISBN 978-0-470-77166-2.
^Olga V. Dorofeeva; Yuriy V. Vishnevskiy; Natalja Vogt; Jürgen Vogt; Lyudmila V. Khristenko; Sergey V. Krasnoshchekov; Igor F. Shishkov; István Hargittai; Lev V. Vilkov (2007). "Molecular Structure and Conformation of Nitrobenzene Reinvestigated by Combined Analysis of Gas-Phase Electron Diffraction, Rotational Constants, and Theoretical Calculations". Structural Chemistry. 18 (6): 739–753. doi:10.1007/s11224-007-9186-6. S2CID 98746905.
^Markofsky, Sheldon; Grace, W.G. (2000). "Nitro Compounds, Aliphatic". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a17_401. ISBN 978-3-527-30673-2.
^Kornblum, N.; Ungnade, H. E. (1963). "1-Nitroöctane". Organic Syntheses. 4: 724. doi:10.15227/orgsyn.038.0075.
^Walden, P. (1907). "Zur Darstellung aliphatischer Sulfocyanide, Cyanide und Nitrokörper". Berichte der Deutschen Chemischen Gesellschaft. 40 (3): 3214–3217. doi:10.1002/cber.19070400383.
^Whitmore, F. C.; Whitmore, Marion G. (1923). "Nitromethane". Organic Syntheses. 1: 401. doi:10.15227/orgsyn.003.0083.
^Olah, George A.; Ramaiah, Pichika; Chang-Soo, Lee; Prakash, Surya (1992). "Convenient Oxidation of Oximes to Nitro Compounds with Sodium Perborate in Glacial Acetic Acid". Synlett. 1992 (4): 337–339. doi:10.1055/s-1992-22006.
^Ehud, Keinan; Yehuda, Mazur (1977). "Dry ozonation of amines. Conversion of primary amines to nitro compounds". The Journal of Organic Chemistry. 42 (5): 844–847. doi:10.1021/jo00425a017.
^Chandrasekhar, S.; Shrinidhi, A. (2014). "Useful Extensions of the Henry Reaction: Expeditious Routes to Nitroalkanes and Nitroalkenes in Aqueous Media". Synthetic Communications. 44 (20): 3008–3018. doi:10.1080/00397911.2014.926373. S2CID 98439096.
^Shrinidhi, A. (2015). "Microwave-assisted chemoselective reduction of conjugated nitroalkenes to nitroalkanes with aqueous tri-n-butyltin hydride". Cogent Chemistry. 1 (1): 1061412. doi:10.1080/23312009.2015.1061412.
^Wislicenus, Wilhelm; Endres, Anton (1902). "Ueber Nitrirung mittels Aethylnitrat [Nitrification by means of ethyl nitrate]". Berichte der Deutschen Chemischen Gesellschaft. 35 (2): 1755–1762. doi:10.1002/cber.190203502106.
^Weygand, Conrad (1972). Hilgetag, G.; Martini, A. (eds.). Weygand/Hilgetag Preparative Organic Chemistry (4th ed.). New York: John Wiley & Sons, Inc. p. 1007. ISBN 978-0-471-93749-4.
^Hawthorne, M. Frederick (1956). "Aci-Nitroalkanes. I. The Mechanism of the ter Meer Reaction1". Journal of the American Chemical Society. 78 (19): 4980–4984. doi:10.1021/ja01600a048.
^3-Hexene, 3,4-dinitro- D. E. Bisgrove, J. F. Brown, Jr., and L. B. Clapp. Organic Syntheses, Coll. Vol. 4, p. 372 (1963); Vol. 37, p. 23 (1957). (Article)
^Zocher, Georg; Winkler, Robert; Hertweck, Christian; Schulz, Georg E (2007). "Structure and Action of the N-oxygenase AurF from Streptomyces thioluteus". Journal of Molecular Biology. 373 (1): 65–74. doi:10.1016/j.jmb.2007.06.014. PMID 17765264.
^Maia, José Guilherme S.; Andrade, Eloísa Helena A. (2009). "Database of the Amazon aromatic plants and their essential oils" (PDF). Química Nova. 32 (3). FapUNIFESP (SciELO): 595–622. doi:10.1590/s0100-40422009000300006. ISSN 0100-4042.
^Kramer, K.U.; Kubitzki, K.; Rohwer, J.G.; Bittrich, V. (1993). Flowering Plants, Dicotyledons: Magnoliid, Hamamelid, and Caryophyllid Families. Families and genera of vascular plants. Springer-Verlag, Berlin. ISBN 978-3-540-55509-4.
^Bordwell, Frederick G; Satish, A. V (1994). "Is Resonance Important in Determining the Acidities of Weak Acids or the Homolytic Bond Dissociation Enthalpies (BDEs) of Their Acidic H-A Bonds?". Journal of the American Chemical Society. 116 (20): 8885. doi:10.1021/ja00099a004.
^Ranganathan, Darshan; Rao, Bhushan; Ranganathan, Subramania; Mehrotra, Ashok & Iyengar, Radha (1980). "Nitroethylene: a stable, clean, and reactive agent for organic synthesis". The Journal of Organic Chemistry. 45 (7): 1185–1189. doi:10.1021/jo01295a003.
^Jubert, Carole & Knochel, Paul (1992). "Preparation of polyfunctional nitro olefins and nitroalkanes using the copper-zinc reagents RCu(CN)ZnI". The Journal of Organic Chemistry. 57 (20): 5431–5438. doi:10.1021/jo00046a027.
^Bartoli, Giuseppe; Marcantoni, Enrico; Petrini, Marino (1992) [14 Apr 1992]. "Nitrones from addition of benzyl and allyl Grignard reagents to alkyl nitro compounds: chemo-, regio-, and stereoselectivity of the reaction". Journal of Organic Chemistry. 57 (22). American Chemical Society: 5834–5840. doi:10.1021/jo00048a012.
^Nagpal, Akanksha; Valley, Michael P.; Fitzpatrick, Paul F.; Orville, Allen M. (2006). "Crystal Structures of Nitroalkane Oxidase: Insights into the Reaction Mechanism from a Covalent Complex of the Flavoenzyme Trapped during Turnover". Biochemistry. 45 (4): 1138–50. doi:10.1021/bi051966w. PMC 1855086. PMID 16430210.
Wikimedia Commons has media related to Nitro compounds.