→Reactions of aliphatic nitro compounds: revert narrow scope (tertiary nitro's are hardly representative)
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[[File:Nitro-group.svg|thumb|right|150px|The structure of an organic nitro compound]] |
[[File:Nitro-group.svg|thumb|right|150px|The structure of an organic nitro compound]] |
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In [[organic chemistry]], '''nitro compounds''' are [[organic compound]]s that contain one or more '''nitro''' [[functional group]]s ({{chem2|\sNO2}}). The nitro group is one of the most common [[explosophore]]s (functional group that makes a compound explosive) used globally. The nitro group is also strongly [[electron-withdrawing group|electron-withdrawing]]. Because of this property, {{chem2|[[Carbon–hydrogen bond|C\sH]]}} 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]].<ref>{{cite book |title=Nitro and Nitroso Groups: Part 2, Volume 2 |year=1970 |editor=Henry Feuer |isbn=9780470771174 |doi=10.1002/9780470771174 |publisher=John Wiley & Sons Ltd. |series=PATAI'S Chemistry of Functional Groups|volume=2 }}{{cite book |title=Nitro and Nitroso Groups: Supplement F: Part 2, Volume 2 |year=1982 |editor=Saul Patai |isbn=9780470771679 |doi=10.1002/9780470771679 |publisher=John Wiley & Sons Ltd. |series=PATAI'S Chemistry of Functional Groups}}{{cite book |title=Amino, Nitroso and Nitro Compounds and Their Derivatives: Supplement F: Part 1, Volume 1 |year=1982 |editor=Saul Patai |isbn=9780470771662 |doi=10.1002/9780470771662 |publisher=John Wiley & Sons Ltd. |series=PATAI'S Chemistry of Functional Groups}}</ref> |
In [[organic chemistry]], '''nitro compounds''' are [[organic compound]]s that contain one or more '''nitro''' [[functional group]]s ({{chem2|\sNO2}}). The nitro group is one of the most common [[explosophore]]s (functional group that makes a compound explosive) used globally. The nitro group is also strongly [[electron-withdrawing group|electron-withdrawing]]. Because of this property, {{chem2|[[Carbon–hydrogen bond|C\sH]]}} 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]].<ref>{{cite book |title=Nitro and Nitroso Groups: Part 2, Volume 2 |year=1970 |editor=Henry Feuer |isbn={{Format ISBN|9780470771174}} |doi=10.1002/9780470771174 |publisher=John Wiley & Sons Ltd. |series=PATAI'S Chemistry of Functional Groups|volume=2 }}{{cite book |title=Nitro and Nitroso Groups: Supplement F: Part 2, Volume 2 |year=1982 |editor=Saul Patai |isbn={{Format ISBN|9780470771679}} |doi=10.1002/9780470771679 |publisher=John Wiley & Sons Ltd. |series=PATAI'S Chemistry of Functional Groups}}{{cite book |title=Amino, Nitroso and Nitro Compounds and Their Derivatives: Supplement F: Part 1, Volume 1 |year=1982 |editor=Saul Patai |isbn={{Format ISBN|9780470771662}} |doi=10.1002/9780470771662 |publisher=John Wiley & Sons Ltd. |series=PATAI'S Chemistry of Functional Groups}}</ref> |
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==Synthesis== |
==Synthesis== |
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===Preparation of aromatic nitro compounds === |
===Preparation of aromatic nitro compounds === |
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[[File:PhNO2&metric.png|thumb|144px|Structural details of [[nitrobenzene]], distances in picometers.<ref>{{cite journal |journal=Structural Chemistry |year=2007 |volume=18 |issue=6 |pages=739–753 |title=Molecular Structure and Conformation of Nitrobenzene Reinvestigated by Combined Analysis of Gas-Phase Electron Diffraction, Rotational Constants, and Theoretical Calculations | |
[[File:PhNO2&metric.png|thumb|144px|Structural details of [[nitrobenzene]], distances in picometers.<ref>{{cite journal |journal=Structural Chemistry |year=2007 |volume=18 |issue=6 |pages=739–753 |title=Molecular Structure and Conformation of Nitrobenzene Reinvestigated by Combined Analysis of Gas-Phase Electron Diffraction, Rotational Constants, and Theoretical Calculations |author=Olga V. Dorofeeva |author2=Yuriy V. Vishnevskiy |author3=Natalja Vogt |author4=Jürgen Vogt |author5=Lyudmila V. Khristenko |author6=Sergey V. Krasnoshchekov |author7=Igor F. Shishkov |author8=István Hargittai |author9=Lev V. Vilkov |doi=10.1007/s11224-007-9186-6 |s2cid=98746905}}</ref>]] |
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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 ({{chem2|NO2+}}), which is the electrophile: |
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 ({{chem2|NO2+}}), which is the electrophile: |
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===Preparation of aliphatic nitro compounds === |
===Preparation of aliphatic nitro compounds === |
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Aliphatic nitro compounds can be synthesized by various methods; notable examples include: |
Aliphatic nitro compounds can be synthesized by various methods; notable examples include: |
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*[[Free radical]] [[nitration]] of [[alkane]]s.<ref>{{cite book|last1=Markofsky|first1=Sheldon|last2=Grace|first2=W.G.|title=Nitro Compounds, Aliphatic|journal=Ullmann's Encyclopedia of Industrial Chemistry|date=2000|doi=10.1002/14356007.a17_401|isbn=978-3527306732}}</ref> The reaction produces fragments from the parent alkane, creating a diverse mixture of products; for instance, [[nitromethane]], [[nitroethane]], [[1-Nitropropane|1-nitropropane]], and [[2-Nitropropane|2-nitropropane]] are produced by treating [[propane]] with [[nitric acid]] in the gas phase (e.g. 350–450 °C and 8–12 [[Atmosphere (unit)|atm]]). |
*[[Free radical]] [[nitration]] of [[alkane]]s.<ref>{{cite book|last1=Markofsky|first1=Sheldon|last2=Grace|first2=W.G.|title=Nitro Compounds, Aliphatic|journal=Ullmann's Encyclopedia of Industrial Chemistry|date=2000|doi=10.1002/14356007.a17_401|isbn={{Format ISBN|978-3527306732}}}}</ref> The reaction produces fragments from the parent alkane, creating a diverse mixture of products; for instance, [[nitromethane]], [[nitroethane]], [[1-Nitropropane|1-nitropropane]], and [[2-Nitropropane|2-nitropropane]] are produced by treating [[propane]] with [[nitric acid]] in the gas phase (e.g. 350–450 °C and 8–12 [[Atmosphere (unit)|atm]]). |
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*[[Nucleophilic substitution]] reactions between [[halocarbon]]s<ref>{{cite journal|last1=Kornblum|first1=N.|last2=Ungnade|first2=H. E.|title=1-Nitroöctane|journal=Organic Syntheses|date=1963|volume=4|page=724|doi=10.15227/orgsyn.038.0075}}</ref> or [[organosulfate]]s<ref>{{cite journal|last1=Walden|first1=P.|title=Zur Darstellung aliphatischer Sulfocyanide, Cyanide und Nitrokörper|journal=Berichte der Deutschen Chemischen Gesellschaft|date=1907|volume=40|issue=3|pages=3214–3217|doi=10.1002/cber.19070400383|url=https://zenodo.org/record/1426247}}</ref> with [[Silver nitrite|silver]] or [[Alkali metal|alkali]] [[nitrite]] salts. |
*[[Nucleophilic substitution]] reactions between [[halocarbon]]s<ref>{{cite journal|last1=Kornblum|first1=N.|last2=Ungnade|first2=H. E.|title=1-Nitroöctane|journal=Organic Syntheses|date=1963|volume=4|page=724|doi=10.15227/orgsyn.038.0075}}</ref> or [[organosulfate]]s<ref>{{cite journal|last1=Walden|first1=P.|title=Zur Darstellung aliphatischer Sulfocyanide, Cyanide und Nitrokörper|journal=Berichte der Deutschen Chemischen Gesellschaft|date=1907|volume=40|issue=3|pages=3214–3217|doi=10.1002/cber.19070400383|url=https://zenodo.org/record/1426247}}</ref> with [[Silver nitrite|silver]] or [[Alkali metal|alkali]] [[nitrite]] salts. |
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*Nitromethane can be produced in the laboratory by treating [[chloroacetic acid|sodium chloroacetate]] with [[sodium nitrite]].<ref>{{cite journal|last1=Whitmore|first1=F. C.|last2=Whitmore|first2=Marion G.|title=Nitromethane|journal=Organic Syntheses|date=1923|volume=1|page=401|doi=10.15227/orgsyn.003.0083}}</ref> |
*Nitromethane can be produced in the laboratory by treating [[chloroacetic acid|sodium chloroacetate]] with [[sodium nitrite]].<ref>{{cite journal|last1=Whitmore|first1=F. C.|last2=Whitmore|first2=Marion G.|title=Nitromethane|journal=Organic Syntheses|date=1923|volume=1|page=401|doi=10.15227/orgsyn.003.0083}}</ref> |
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*[[Organic redox reaction|Oxidation]] of [[oxime]]s<ref>{{cite journal|last1=Olah|first1=George A.|last2=Ramaiah|first2=Pichika|last3=Chang-Soo|first3=Lee|last4=Prakash|first4=Surya|title=Convenient Oxidation of Oximes to Nitro Compounds with Sodium Perborate in Glacial Acetic Acid|journal=Synlett|date=1992|volume=1992|issue=4|pages=337–339|doi=10.1055/s-1992-22006}}</ref> or [[Primary (chemistry)|primary]] [[amine]]s.<ref>{{cite journal|last1=Ehud|first1=Keinan|last2=Yehuda|first2=Mazur|title=Dry ozonation of amines. Conversion of primary amines to nitro compounds|journal=The Journal of Organic Chemistry|date=1977|volume=42|issue=5|pages=844–847|doi=10.1021/jo00425a017}}</ref> |
*[[Organic redox reaction|Oxidation]] of [[oxime]]s<ref>{{cite journal|last1=Olah|first1=George A.|last2=Ramaiah|first2=Pichika|last3=Chang-Soo|first3=Lee|last4=Prakash|first4=Surya|title=Convenient Oxidation of Oximes to Nitro Compounds with Sodium Perborate in Glacial Acetic Acid|journal=Synlett|date=1992|volume=1992|issue=4|pages=337–339|doi=10.1055/s-1992-22006}}</ref> or [[Primary (chemistry)|primary]] [[amine]]s.<ref>{{cite journal|last1=Ehud|first1=Keinan|last2=Yehuda|first2=Mazur|title=Dry ozonation of amines. Conversion of primary amines to nitro compounds|journal=The Journal of Organic Chemistry|date=1977|volume=42|issue=5|pages=844–847|doi=10.1021/jo00425a017}}</ref> |
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*Reduction of [[Henry reaction|β-nitro alcohols]]<ref>{{cite journal |last1=Chandrasekhar |first1=S. |last2=Shrinidhi |first2=A. |title=Useful Extensions of the Henry Reaction: Expeditious Routes to Nitroalkanes and Nitroalkenes in Aqueous Media |journal=Synthetic Communications |date=2014 |volume=44 |issue=20 |pages=3008–3018 |doi=10.1080/00397911.2014.926373|s2cid=98439096 |url=https://figshare.com/articles/journal_contribution/1053153 }}</ref> or [[nitroalkene]]s.<ref>{{cite journal |last1=Shrinidhi |first1=A. |title=Microwave-assisted chemoselective reduction of conjugated nitroalkenes to nitroalkanes with aqueous tri-n-butyltin hydride |journal=Cogent Chemistry |date=2015 |volume=1 |issue=1 | |
*Reduction of [[Henry reaction|β-nitro alcohols]]<ref>{{cite journal |last1=Chandrasekhar |first1=S. |last2=Shrinidhi |first2=A. |title=Useful Extensions of the Henry Reaction: Expeditious Routes to Nitroalkanes and Nitroalkenes in Aqueous Media |journal=Synthetic Communications |date=2014 |volume=44 |issue=20 |pages=3008–3018 |doi=10.1080/00397911.2014.926373|s2cid=98439096 |url=https://figshare.com/articles/journal_contribution/1053153 }}</ref> or [[nitroalkene]]s.<ref>{{cite journal |last1=Shrinidhi |first1=A. |title=Microwave-assisted chemoselective reduction of conjugated nitroalkenes to nitroalkanes with aqueous tri-n-butyltin hydride |journal=Cogent Chemistry |date=2015 |volume=1 |issue=1 |page=1061412 |doi=10.1080/23312009.2015.1061412|doi-access=free }}</ref> |
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*By [[decarboxylation]] of [[alpha and beta carbon|α]]-nitro [[carboxylic acid]]s formed from [[nitriles]] and [[ethyl nitrate]].<ref>{{cite journal|last1=Wislicenus|first1=Wilhelm|last2=Endres|first2=Anton|title=Ueber Nitrirung mittels Aethylnitrat [Nitrification by means of ethyl nitrate]|journal=Berichte der Deutschen Chemischen Gesellschaft|date=1902|volume=35|issue=2|pages=1755–1762|doi=10.1002/cber.190203502106|url=https://zenodo.org/record/1426046}}</ref><ref>{{cite book|last1=Weygand|first1=Conrad|editor1-last=Hilgetag|editor1-first=G.|editor2-last=Martini|editor2-first=A.|title=Weygand/Hilgetag Preparative Organic Chemistry|date=1972|publisher=John Wiley & Sons, Inc.|location=New York|isbn=978-0471937494|page=1007|edition=4th}}</ref> |
*By [[decarboxylation]] of [[alpha and beta carbon|α]]-nitro [[carboxylic acid]]s formed from [[nitriles]] and [[ethyl nitrate]].<ref>{{cite journal|last1=Wislicenus|first1=Wilhelm|last2=Endres|first2=Anton|title=Ueber Nitrirung mittels Aethylnitrat [Nitrification by means of ethyl nitrate]|journal=Berichte der Deutschen Chemischen Gesellschaft|date=1902|volume=35|issue=2|pages=1755–1762|doi=10.1002/cber.190203502106|url=https://zenodo.org/record/1426046}}</ref><ref>{{cite book|last1=Weygand|first1=Conrad|editor1-last=Hilgetag|editor1-first=G.|editor2-last=Martini|editor2-first=A.|title=Weygand/Hilgetag Preparative Organic Chemistry|date=1972|publisher=John Wiley & Sons, Inc.|location=New York|isbn={{Format ISBN|978-0471937494}}|page=1007|edition=4th}}</ref> |
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====Ter Meer Reaction==== |
====Ter Meer Reaction==== |
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===Acid-base reactions=== |
===Acid-base reactions=== |
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The α-carbon of nitroalkanes is somewhat acidic. The p''K''<sub>a</sub> values of [[nitromethane]] and [[2-nitropropane]] are respectively 17.2 and 16.9 in [[dimethyl sulfoxide]] (DMSO) solution. These values suggest an aqueous p''K''<sub>a</sub> of around 11.<ref>{{cite journal | doi = 10.1021/ja00099a004| title = Is Resonance Important in Determining the Acidities of Weak Acids or the Homolytic Bond Dissociation Enthalpies (BDEs) of Their Acidic H-A Bonds?| journal = Journal of the American Chemical Society| volume = 116| issue = 20| |
The α-carbon of nitroalkanes is somewhat acidic. The p''K''<sub>a</sub> values of [[nitromethane]] and [[2-nitropropane]] are respectively 17.2 and 16.9 in [[dimethyl sulfoxide]] (DMSO) solution. These values suggest an aqueous p''K''<sub>a</sub> of around 11.<ref>{{cite journal | doi = 10.1021/ja00099a004| title = Is Resonance Important in Determining the Acidities of Weak Acids or the Homolytic Bond Dissociation Enthalpies (BDEs) of Their Acidic H-A Bonds?| journal = Journal of the American Chemical Society| volume = 116| issue = 20| page = 8885| year = 1994| last1 = Bordwell| first1 = Frederick G| last2 = Satish| first2 = A. V}}</ref> In other words, these [[carbon acid]]s can be deprotonated in aqueous solution. The conjugate base is called a [[nitronate]], they are formed as intermediates in the [[nitroaldol reaction]] and [[Nef reaction]]s. |
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===Condensation reactions=== |
===Condensation reactions=== |
Inorganic chemistry, nitro compounds are organic compounds that contain one or more nitro functional 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]
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:
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.
Aliphatic nitro compounds can be synthesized by various methods; notable examples include:
Innucleophilic aliphatic substitution, sodium nitrite (NaNO2) replaces an alkyl halide. In the so-called Ter Meer reaction (1876) named after Edmund ter Meer,[14] the reactant is a 1,1-halonitroalkane:
The reaction mechanism is proposed in which in the first slow step a proton is abstracted from nitroalkane 1 to a carbanion 2 followed by protonation to an aci-nitro 3 and finally nucleophilic displacement of chlorine based on an experimentally observed hydrogen kinetic isotope effect of 3.3.[15] When the same reactant is reacted with potassium hydroxide the reaction product is the 1,2-dinitro dimer.[16]
Chloramphenicol is a rare example of a naturally occurring nitro compound. At least some naturally occurring nitro groups arose by the oxidation of amino groups.[17] 2-Nitrophenol is an aggregation pheromoneofticks.
Examples of nitro compounds are rare in nature. 3-Nitropropionic acid found in fungi and plants (Indigofera). Nitropentadecene is a defense compound found in termites. Nitrophenylethane is found in Aniba canelilla.[18] Nitrophenylethane is also found in members of the Annonaceae, Lauraceae and Papaveraceae.[19]
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]
Nitro compounds participate in several organic reactions, the most important being their reduction to the corresponding amines:
Variations on this method is one of the main techniques for arylamine production.
In the Nef reaction, a nitro compound hydrolyzes to release a ketone/aldehyde and nitrous oxide.
The α-carbon of nitroalkanes is somewhat acidic. The pKa values of nitromethane and 2-nitropropane are respectively 17.2 and 16.9 in dimethyl sulfoxide (DMSO) solution. These values suggest an aqueous pKa of around 11.[21] In other words, these carbon acids can be deprotonated in aqueous solution. The conjugate base is called a nitronate, they are formed as intermediates in the nitroaldol reaction and Nef reactions.
Nitromethane undergoes base-catalyzed additions to aldehydes in 1,2-addition in the nitroaldol reaction. Similarly, it adds to alpha-beta unsaturated carbonyl compounds as a 1,4-addition in the Michael reaction as a Michael donor. Nitroalkenes are Michael acceptors in the Michael reaction with enolate compounds.[22][23]
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.[24]
Reduction of aromatic nitro compounds with hydrogen over metal catalysts gives anilines. Virtually all aromatic amines (anilines) are derived from nitroaromatics. A variation is formation of a dimethylaminoarene with palladium on carbon and formaldehyde:[25]
The Leimgruber–Batcho, Bartoli and Baeyer–Emmerling indole syntheses begin with aromatic nitro compounds. Indigo can be synthesized in a condensation reaction from ortho-nitrobenzaldehyde and acetone in strongly basic conditions in a reaction known as the Baeyer–Drewson indigo synthesis.
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.
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Only one element, not being carbon, hydrogen, or oxygen (one element, not C, H or O) |
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Nitrogen species
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Hydrides |
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Organic |
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Halides |
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Oxidation states |