In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...
, nitroso refers to a
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...
in which the
nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
() group is attached to an organic
moiety
Moiety may refer to:
Chemistry
* Moiety (chemistry), a part or functional group of a molecule
** Moiety conservation, conservation of a subgroup in a chemical species
Anthropology
* Moiety (kinship), either of two groups into which a society is ...
. As such, various nitroso groups can be categorized as ''C''-nitroso compounds (e.g., nitroso
alkane
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which ...
s; ), ''S''-nitroso compounds (
nitrosothiols; ), ''N''-nitroso compounds (e.g.,
nitrosamines
In organic chemistry, nitrosamines (or more formally ''N''-Nitrosamines) are organic compounds with the chemical structure , where R is usually an alkyl group. They feature a nitroso group () bonded to a deprotonated amine. Most nitrosamines are ...
, ), and ''O''-nitroso compounds (
alkyl nitrites; ).
Synthesis
Nitroso compounds can be prepared by the reduction of
nitro compound
In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups (). The nitro group is one of the most common explosophores (functional group that makes a compound explosive) used globally. The nitr ...
s or by the oxidation of
hydroxylamine
Hydroxylamine is an inorganic compound with the formula . The material is a white crystalline, hygroscopic compound.Greenwood and Earnshaw. ''Chemistry of the Elements.'' 2nd Edition. Reed Educational and Professional Publishing Ltd. pp. 431–43 ...
s.
Ortho-nitrosophenols may be produced by the
Baudisch reaction
In organic chemistry, the Baudisch reaction is a process for the synthesis of nitrosophenols using metal ions. Although the products are of limited value, the reaction is of historical interest as an example of metal-promoted functionalization of a ...
. In the
Fischer–Hepp rearrangement aromatic 4-nitrosoanilines are prepared from the corresponding
nitrosamine
In organic chemistry, nitrosamines (or more formally ''N''-Nitrosamines) are organic compounds with the chemical structure , where R is usually an alkyl group. They feature a nitroso group () bonded to a deprotonated amine. Most nitrosamines are ...
s.
Properties
![VIYMEX](https://upload.wikimedia.org/wikipedia/commons/3/35/VIYMEX.png)
Nitrosoarenes typically participate in a
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.
Due to the stability of the nitric oxide
free radical
A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing.
Ageing
Ailments of unknown cause
Biogerontology
Biological processes
Causes of death
Cellular processes
Gerontology
Life extension
Metabo ...
, nitroso organyls tend to have very low C–N
bond dissociation energies
The bond-dissociation energy (BDE, ''D''0, or ''DH°'') is one measure of the strength of a chemical bond . It can be defined as the standard enthalpy change when is cleaved by homolysis to give fragments A and B, which are usually radical s ...
: nitrosoalkanes have BDEs on the order of , while nitrosoarenes have BDEs on the order of . 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,
''N''-nitrosodiphenylamine, Ph
2N–N=O, has a N–N bond dissociation energy of only . Organonitroso compounds serve as a
ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
s for
transition metal
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...
s.
Reactions
Many reaction exists which make use of an intermediate nitroso compound, such as the
Barton reaction The Barton reaction, also known as the Barton nitrite ester reaction, is a photochemical reaction that involves the photolysis of an alkyl nitrite to form a δ-nitroso alcohol.
Discovered in 1960, the reaction is named for its discoverer, Nobel Lau ...
and
Davis–Beirut reaction
The Davis–Beirut reaction is ''N,N''-bond forming heterocyclization that creates numerous types of 2''H''-indazoles and indazolones in both acidic and basic conditions
The Davis–Beirut reaction is named after Mark Kurth and Makhluf Haddadin ...
, as well as in the synthesis of
indole
Indole is an aromatic heterocyclic organic compound with the formula C8 H7 N. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indole is widely distributed in the natural environmen ...
s, for example:
Baeyer–Emmerling indole synthesis
The Baeyer–Emmerling indole synthesis is a method for synthesizing indole from a (substituted) ''ortho''-nitrocinnamic acid and iron powder in strongly basic solution. This reaction was discovered by Adolf von Baeyer and Adolph Emmerling in 186 ...
,
Bartoli indole synthesis
The Bartoli indole synthesis (also called the Bartoli reaction) is the chemical reaction of ortho-substituted nitroarenes and nitrosoarenes with vinyl Grignard reagents to form substituted indoles.
The reaction is often unsuccessful without sub ...
. In the
Saville reaction
The Saville reaction is a chemical reaction in which mercury replaces a nitrosyl from a thiol group.
It is used as a method of replacing the nitrosyl from the modified cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic ...
, mercury is used to replace a nitrosyl from a thiol group.
Nitrosation vs. nitrosylation
Nitrite
The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...
can enter two kinds of reaction, depending on the physico-chemical environment.
*
Nitrosylation
Nitrosylation is the general term for covalent incorporation of a nitric oxide "nitrosyl" moiety into another (usually organic) molecule. There are multiple chemical mechanisms by which this can be achieved; including biological enzymes and indust ...
is adding a
nitrosyl ion to a metal (e.g. iron) or a thiol, leading to nitrosyl iron (e.g., in nitrosylated heme = nitrosylheme) or ''S''-nitrosothiols (RSNOs).
*
Nitrosation
Nitrosation is a process of converting organic compounds into nitroso derivatives, i.e. compounds containing the R-NO functionality.
''C''-Nitroso compounds
''C''-Nitroso compounds, such as nitrosobenzene, are typically prepared by oxidation of ...
is adding a
nitrosonium ion
The nitrosonium ion is , in which the nitrogen atom is bonded to an oxygen atom with a bond order of 3, and the overall diatomic species bears a positive charge. It can be viewed as nitric oxide with one electron removed. This ion is usually obt ...
to an amine – leading to a
nitrosamine
In organic chemistry, nitrosamines (or more formally ''N''-Nitrosamines) are organic compounds with the chemical structure , where R is usually an alkyl group. They feature a nitroso group () bonded to a deprotonated amine. Most nitrosamines are ...
. This conversion occurs at acidic pH, particularly in the stomach, as shown in the equation for the formation of ''N''-phenylnitrosamine:
*:
NO2- + H+ <=> HONO
*:
HONO + H+ <=> H2O + NO+
*:
C6H5NH2 + NO+ -> C6H5N(H)NO + H+
Many primary alkyl ''N''-nitroso compounds, such as , tend to be unstable with respect to hydrolysis to the alcohol. Those derived from secondary amines (e.g., derived from
dimethylamine
Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to aroun ...
) are more robust. It is these ''N''-nitrosamines that are carcinogens in rodents.
Nitrosyl in inorganic chemistry
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
nonmetal
In chemistry, a nonmetal is a chemical element that generally lacks a predominance of metallic properties; they range from colorless gases (like hydrogen) to shiny solids (like carbon, as graphite). The electrons in nonmetals behave differentl ...
example is the common reagent
nitrosyl chloride
Nitrosyl chloride is the chemical compound with the formula NOCl. It is a yellow gas that is commonly encountered as a component of aqua regia, a mixture of 3 parts concentrated hydrochloric acid and 1 part of concentrated nitric acid. It is a st ...
(). Nitric oxide is a stable
radical
Radical may refer to:
Politics and ideology Politics
*Radical politics, the political intent of fundamental societal change
*Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...
, having an unpaired electron. Reduction of nitric oxide gives the nitrosyl
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
, :
:
NO + e- -> NO-
Oxidation of NO yields the
nitrosonium cation
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
, :
:
NO -> NO+ + e-
Nitric oxide can serve as a
ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
forming
metal nitrosyl complexes or just metal nitrosyls. These complexes can be viewed as adducts of , , or some intermediate case.
In food
In foodstuffs and in the gastro-intestinal tract, nitrosation and nitrosylation do not have the same consequences on consumer health.
* In
cured meat
Curing is any of various food preservation and flavoring processes of foods such as meat, fish and vegetables, by the addition of salt, with the aim of drawing moisture out of the food by the process of osmosis. Because curing increases the sol ...
: Meat processed by
curing contains nitrite and has a pH of 5 approximately, where almost all nitrite is present as (99%). Cured meat is also added with
sodium ascorbate
Sodium ascorbate is one of a number of mineral salts of ascorbic acid (vitamin C). The molecular formula of this chemical compound is C6H7NaO6. As the sodium salt of ascorbic acid, it is known as a mineral ascorbate. It has not been demonstrate ...
(or erythorbate or vitamin C). As demonstrated by S. Mirvish, ascorbate inhibits nitrosation of amines to nitrosamine, because ascorbate reacts with to form NO. Ascorbate and pH 5 thus favor nitrosylation of heme iron, forming nitrosylheme, a red pigment when included inside myoglobin, and a pink pigment when it has been released by cooking. It participates to the "bacon flavor" of cured meat. According to a consultant for the European lobby for processed meats K-O Honikel, nitrosylheme is thus considered a benefit for the
meat industry
The meat industry are the people and companies engaged in modern industrialized livestock agriculture for the production, packing, preservation and marketing of meat (in contrast to dairy products, wool, etc.). In economics, the meat industry is ...
and for consumers. According to scientists outside of the processed-meat industry, nitrosylheme is considered a carcinogenic compound.
* In the
stomach
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
: secreted
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
makes an acidic environment (pH 2) and ingested nitrite (with food or saliva) leads to nitrosation of amines, that yields
nitrosamine
In organic chemistry, nitrosamines (or more formally ''N''-Nitrosamines) are organic compounds with the chemical structure , where R is usually an alkyl group. They feature a nitroso group () bonded to a deprotonated amine. Most nitrosamines are ...
s (potential carcinogens). Nitrosation is low if amine concentration is low (e.g., low-protein diet, no fermented food) or if vitamin C concentration is high (e.g., high fruit diet). Then ''S''-nitrosothiols are formed, that are stable at pH 2.
* In the
colon: neutral pH does not favor nitrosation. No nitrosamine is formed in stools, even after addition of a secondary amine or nitrite. Neutral pH favors release from ''S''-nitrosothiols, and nitrosylation of iron. The previously called NOC (''N''-nitroso compounds) measured by Bingham's team in stools from red meat-fed volunteers were, according to Bingham and Kuhnle, largely non-''N''-nitroso ATNC (apparent total nitroso compounds), e.g., ''S''-nitrosothiols and nitrosyl iron (as nitrosyl heme).
See also
*
Nitrosamine
In organic chemistry, nitrosamines (or more formally ''N''-Nitrosamines) are organic compounds with the chemical structure , where R is usually an alkyl group. They feature a nitroso group () bonded to a deprotonated amine. Most nitrosamines are ...
, the functional group with the NO attached to an amine, such as R
2N–NO
*
Nitrosobenzene
Nitrosobenzene is the organic compound with the chemical formula, formula C6H5NO. It is one of the prototypical organic nitroso compounds. Characteristic of its functional group, it is a dark green species that exists in equilibrium with its pale ...
*
Nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
*
Nitroxyl
Nitroxyl (common name) or azanone (IUPAC name) is the chemical compound HNO. It is well known in the gas phase. Nitroxyl can be formed as a short-lived intermediate in the solution phase. The conjugate base, NO−, nitroxide anion, is the redox re ...
References
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Functional groups
Nitrosyl compounds
In organic chemistry, nitroso refers to a functional group in which the nitric oxide () group is attached to an organic moiety. As such, various nitroso groups can be categorized as ''C''-nitroso compounds (e.g., nitrosoalkanes; ), ''S''-nitroso ...