View source for Chemistry:Nitroso

{{Short description|1=Class of functional groups with a –N=O group attached}}
[[Image:Nitroso-compound-2D.svg| thumb | right | [[Chemistry:Structural formula|Structural formula]] of nitroso group]]

In [[Chemistry:Organic chemistry|organic chemistry]], '''nitroso''' refers to a [[Chemistry:Functional group|functional group]] in which the [[Chemistry:Nitric oxide|nitric oxide]] ({{chem2|\sN\dO}}) group is attached to an organic [[Chemistry:Moiety|moiety]]. As such, various nitroso groups can be categorized as ''C''-nitroso compounds (e.g., nitroso[[Chemistry:Alkane|alkane]]s; {{chem2|R\sN\dO}}), ''S''-nitroso compounds ([[Chemistry:S-Nitrosothiol|nitrosothiols]]; {{chem2|RS\sN\dO}}), ''N''-nitroso compounds (e.g., nitrosamines, {{chem2|RN(\sR’)\sN\dO}}), and ''O''-nitroso compounds ([[Chemistry:Alkyl nitrites|alkyl nitrites]]; {{chem2|RO\sN\dO}}).

==Synthesis==
Nitroso compounds can be prepared by the reduction of [[Chemistry:Nitro compound|nitro compound]]s<ref>{{cite journal| author = G. H. Coleman| author2 = C. M. McCloskey| author3 = F. A. Stuart | title = Nitrosobenzene | journal=Org. Synth.|volume = 25 | pages = 80| year = 1945 | doi=10.15227/orgsyn.025.0080}}</ref> or by the oxidation of [[Chemistry:Hydroxylamine|hydroxylamine]]s.<ref>{{OrgSynth|first1=A. |last1=Calder |first2=A. R. |last2=Forrester |first3=S. P. |last3=Hepburn |title=2-Methyl-2-nitrosopropane and Its Dimer |collvol=6 |collvolpages=803 |volume=52 |page=77 |prep=cv6p0803}}</ref> 
Ortho-nitrosophenols may be produced by the [[Chemistry:Baudisch reaction|Baudisch reaction]]. In the [[Chemistry:Fischer–Hepp rearrangement|Fischer–Hepp rearrangement]] aromatic 4-nitrosoanilines are prepared from the corresponding [[Chemistry:Nitrosamine|nitrosamine]]s.

==Properties==
[[File:VIYMEX.png|thumb|right|132px|Structure of 2-nitrosotoluene dimer<ref>{{cite journal|author=E.Bosch|title=Structural Analysis of Methyl-Substituted Nitrosobenzenes and Nitrosoanisoles|journal=J. Chem. Cryst.|year=2014|volume=98|issue=2|page=44| doi=10.1007/s10870-013-0489-8|s2cid=95291018}}</ref>]]

Nitrosoarenes typically participate in a [[Chemistry:Dimerization|monomer–dimer equilibrium]].  The dimers, which are often pale yellow, are often favored in the solid state, whereas the deep-green monomers are favored in dilute solution or at higher temperatures.  They exist as ''cis'' and ''trans'' isomers.<ref>{{cite journal|author1=Beaudoin, D. |author2=Wuest, J. D. |title=Dimerization of Aromatic ''C''-Nitroso Compounds|journal=Chemical Reviews|year=2016|volume=116|issue=1 |pages=258–286|doi=10.1021/cr500520s|pmid=26730505}}</ref>

When stored in [[Chemistry:Protic solvent|protic media]], [[Chemistry:Primary carbon|primary]] and [[Chemistry:Secondary carbon|secondary]] nitrosoalkanes [[Chemistry:Rearrangement reaction|isomerize]] to [[Chemistry:Oxime|oxime]]s.<ref name=TildenLect>{{cite journal |doi=10.1039/CS9770600001|title=Electrophilic C-nitroso-compounds|year=1977|last1=Kirby|first1=G.&nbsp;W.|journal=Chemical Society Reviews|volume=6|page=2|postscript=none}} (Tilden lecture).</ref>  

Due to the stability of the nitric oxide [[Biology:Free radical|free radical]], nitroso organyls tend to have very low C–N bond dissociation energies: nitrosoalkanes have BDEs on the order of {{cvt|30|-|40|kcal/mol|kJ/mol|-1}}, while nitrosoarenes have BDEs on the order of {{cvt|50|-|60|kcal/mol|kJ/mol|-1}}.  As a consequence, they are generally heat- and light-sensitive.  Compounds containing O–(NO) or N–(NO) bonds generally have even lower bond dissociation energies.  For instance, [[Chemistry:N-Nitrosodiphenylamine|''N''-nitrosodiphenylamine]], Ph<sub>2</sub>N–N=O, has a N–N bond dissociation energy of only {{cvt|23|kcal/mol|kJ/mol|0}}.<ref>{{Cite book|title=Comprehensive Handbook of Chemical Bond Energies|last=Luo|first=Yu-Ran|publisher=Taylor and Francis|year=2007|isbn=9781420007282|location=Boca Raton, FL}}</ref> Organonitroso compounds serve as a [[Chemistry:Ligand|ligand]]s giving [[Chemistry:Transition metal nitroso complexes|transition metal nitroso complexes]].<ref name=GBRA>{{cite journal |doi=10.1021/cr0000731 |title=Interactions of Organic Nitroso Compounds with Metals |date=2002 |last1=Lee |first1=Jonghyuk |last2=Chen |first2=Li |last3=West |first3=Ann H. |last4=Richter-Addo |first4=George B. |journal=Chemical Reviews |volume=102 |issue=4 |pages=1019–1066 |pmid=11942786 }}</ref>

==Reactions==
Many reaction exists which make use of an intermediate nitroso compound, such as the [[Chemistry:Barton reaction|Barton reaction]] and [[Chemistry:Davis–Beirut reaction|Davis–Beirut reaction]], as well as in the synthesis of [[Chemistry:Indole|indole]]s, for example: [[Chemistry:Baeyer–Emmerling indole synthesis|Baeyer–Emmerling indole synthesis]], [[Chemistry:Bartoli indole synthesis|Bartoli indole synthesis]]. In the [[Chemistry:Saville reaction|Saville reaction]], mercury is used to replace a nitrosyl from a thiol group.

''C''-nitroso compounds are used in organic synthesis as synthons in some well-documented chemical reactions such as hetero Diels-Alder (HDA), nitroso-ene and nitroso-aldol reactions.<ref>{{cite journal|author1=Bianchi, P. |author2=Monbaliu, J. C. M. |title=Three decades of unveiling the complex chemistry of ''C''-nitroso species with computational chemistry|journal=Organic Chemistry Frontiers|year=2022|volume=9|pages=223–264|doi=10.1039/d1qo01415c}}</ref>

== Nitrosation vs. nitrosylation ==
[[Chemistry:Nitrite|Nitrite]] can enter two kinds of reaction, depending on the physico-chemical environment. 
* [[Chemistry:Nitrosylation|Nitrosylation]] is adding a [[Chemistry:Nitric oxide|nitrosyl ion]] {{chem2|NO-}} to a metal (e.g. iron) or a thiol, leading to nitrosyl iron {{chem2|Fe\sNO}} (e.g., in nitrosylated heme = nitrosylheme) or ''S''-nitrosothiols (RSNOs).
* [[Chemistry:Nitrosation|Nitrosation]] is adding a nitrosonium ion {{chem2|NO+}} to an amine –{{chem2|NH2}} leading to a [[Chemistry:Nitrosamine|nitrosamine]]. This conversion occurs at acidic pH, particularly in the stomach, as shown in the equation for the formation of ''N''-phenylnitrosamine:
*: <chem>NO2- + H+ <=> HONO</chem>
*: <chem>HONO + H+ <=> H2O + NO+</chem>
*: <chem>C6H5NH2 + NO+ -> C6H5N(H)NO + H+</chem>
Many primary alkyl ''N''-nitroso compounds, such as {{chem2|CH3N(H)NO}}, tend to be unstable with respect to hydrolysis to the alcohol. Those derived from secondary amines (e.g., {{chem2|(CH3)2NNO}} derived from [[Chemistry:Dimethylamine|dimethylamine]]) are more robust. It is these ''N''-nitrosamines that are carcinogens in rodents.

==Nitrosyl in inorganic chemistry==
[[Image:Metal-nitrosyl-coordination-modes-2D.png|thumb|right|100px|Linear and bent metal nitrosyls]]
Nitrosyls are non-organic compounds containing the NO group, for example directly bound to the metal via the N atom, giving a metal–NO moiety. Alternatively, a [[Chemistry:Nonmetal|nonmetal]] example is the common reagent [[Chemistry:Nitrosyl chloride|nitrosyl chloride]] ({{chem2|Cl\sN\dO}}). Nitric oxide is a stable [[Biology:Radical|radical]], having an unpaired electron. Reduction of nitric oxide gives the nitrosyl anion, {{chem2|NO-}}:
:<chem>NO + e- -> NO-</chem>

Oxidation of NO yields the [[Chemistry:Nitrosonium|nitrosonium]] cation, {{chem2|NO+}}:
:<chem>NO -> NO+ + e-</chem>

Nitric oxide can serve as a [[Chemistry:Ligand|ligand]] forming metal nitrosyl complexes or just metal nitrosyls. These complexes can be viewed as adducts of {{chem2|NO+}}, {{chem2|NO-}}, or some intermediate case.

==In human health==
{{Transcluded section|source=Nitrosamine formation during digestion}}{{:Nitrosamine formation during digestion}}

== See also ==
* [[Chemistry:Nitrosamine|Nitrosamine]], the functional group with the NO attached to an amine, such as R<sub>2</sub>N–NO
* [[Chemistry:Nitrosobenzene|Nitrosobenzene]]
* [[Chemistry:Nitric oxide|Nitric oxide]]
* [[Chemistry:Nitroxyl|Nitroxyl]]

==References==
{{Reflist}}

{{Functional Groups}}
{{Nitric oxide signaling}}
{{Nitrogen compounds}}

[[Category:Functional groups]]
[[Category:Nitroso compounds| ]]
[[Category:Nitrosyl compounds|Nitrosyl compounds]]

{{Sourceattribution|Nitroso}}