The diazo group is 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 ...
consisting of two linked
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
atoms (
azo) at the terminal position. Overall charge neutral
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s containing the diazo group bound to a carbon atom are called diazo compounds or diazoalkanes and are described by the general structural formula R
2C=N
+=N
–. The simplest example of a diazo compound is
diazomethane, CH
2N
2. Diazo compounds (R
2C=N
2) should not be confused with
azo compounds of the type R-N=N-R or with
diazonium compound
Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide.
General propert ...
s of the type R-N
2+.
Structure
The
electronic structure of diazo compounds is characterized by π electron density delocalized over the α-carbon and two nitrogen atoms, along with an orthogonal π system with electron density delocalized over only the terminal nitrogen atoms. Because all
octet rule-satisfying resonance forms of diazo compounds have formal charges, they are members of a class of compounds known as
1,3-dipoles. Some of the most stable diazo compounds are α-diazo-β-diketones and α-diazo-β-diesters, in which the electron density is further delocalized into an electron-withdrawing carbonyl group. In contrast, most diazoalkanes without electron-withdrawing substituents, including diazomethane itself, are explosive. A commercially relevant diazo compound is
ethyl diazoacetate (N
2CHCOOEt). A group of isomeric compounds with only few similar properties are the
diazirines, where the carbon and two nitrogens are linked as a ring.
Four
resonance structures can be drawn:
:
Compounds with the diazo moiety should be distinguished from ''
diazonium'' compounds, which have the same terminal azo group but bear an overall positive charge, and ''azo'' compounds in which the azo group bridges two organic substituents.
History
Diazo compounds were first produced by
Peter Griess who had discovered a versatile new chemical reaction, as detailed in his 1858 paper "Preliminary notice on the influence of nitrous acid on aminonitro- and aminodinitrophenol."
Synthesis
Several methods exist for the preparation of diazo compounds.
From amines
Alpha-acceptor-substituted primary aliphatic
amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...
s R-CH
2-NH
2 (R = COOR, CN, CHO, COR) react with
nitrous acid to generate the diazo compound.
From diazomethyl compounds
An example of an
electrophilic substitution
Electrophilic substitution reactions are chemical reactions in which an electrophile displaces a functional group in a compound, which is typically, but not always, aromatic. Aromatic substitution reactions are characteristic of aromatic compound ...
using a diazomethyl compound is that of a reaction between an
acyl halide
In organic chemistry, an acyl halide (also known as an acid halide) is a chemical compound derived from an oxoacid by replacing a hydroxyl group () with a halide group (, where X is a halogen).
If the acid is a carboxylic acid (), the compoun ...
and
diazomethane, for example the first step in the
Arndt-Eistert synthesis.
By diazo transfer
In diazo transfer certain
carbon acids react with
tosyl azide in the presence of a weak base like triethylamine or DBU. The byproduct is the corresponding tosylamide (''p''-toluenesulfonamide). This reaction is also called the Regitz diazo transfer. Examples are the synthesis of tert-butyl diazoacetate and diazomalonate.
Methyl phenyldiazoacetate is generated in this way by treating methyl phenylacetate with p-acetamidobenzenesulfonyl azide in the presence of base.
The mechanism involves attack of the enolate at the terminal nitrogen, proton transfer, and expulsion of the anion of the sulfonamide. Use of the β-carbonyl aldehyde leads to a deformylative variant of the Regitz transfer, which is useful for the preparation of diazo compounds stabilized by only one carbonyl group.
From ''N''-alkyl-''N''-nitroso compounds
Diazo compounds can be obtained in an
elimination reaction of ''N''-alkyl-''N''-nitroso compounds, such as in the synthesis of diazomethane from Diazald or
MNNG:
:
:
(The mechanism shown here is one possibility. For an alternative mechanism for the analogous formation of diazomethane from an ''N-''nitrososulfonamide, see the page on
Diazald.)
From hydrazones
Hydrazone
Hydrazones are a class of organic compounds with the structure . They are related to ketones and aldehydes by the replacement of the oxygen =O with the = functional group. They are formed usually by the action of hydrazine on ketones or aldehy ...
s are
oxidized
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
(
dehydrogenation
In chemistry, dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. A ...
) for example with
silver oxide or
mercury oxide Mercury oxide can refer to:
* Mercury(I) oxide (mercurous oxide), Hg2O
* Mercury(II) oxide
Mercury(II) oxide, also called mercuric oxide or simply mercury oxide, is the inorganic compound with the formula Hg O. It has a red or orange color. Mer ...
for example the synthesis of ''2-''diazopropane from acetone hydrazone. Other oxidizing reagents are
lead tetraacetate
Lead(IV) acetate or lead tetraacetate is an organometallic compound with chemical formula . It is a colorless solid that is soluble in nonpolar, organic solvents, indicating that it is not a salt. It is degraded by moisture and is typically st ...
,
manganese dioxide
Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for is for dry-ce ...
and the
Swern reagent.
Tosyl hydrazones RRC=N-NHTs are reacted with base for example
triethylamine
Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA ...
in the synthesis of crotyl diazoacetate and in the synthesis of
phenyldiazomethane from PhCHNHTs and
sodium methoxide.
Reaction of a
carbonyl group with the
hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
1,2-bis(tert-butyldimethylsilyl)hydrazine to form the hydrazone is followed by reaction with the
iodane difluoroiodobenzene yields the diazo compound:
:
From azides
One method is described for the synthesis of diazo compounds from
azide
In chemistry, azide is a linear, polyatomic anion with the formula and structure . It is the conjugate base of hydrazoic acid . Organic azides are organic compounds with the formula , containing the azide functional group. The dominant appli ...
s using
phosphines:
:
Reactions
In cycloadditions
Diazo compounds react as 1,3-dipoles in
diazoalkane 1,3-dipolar cycloadditions.
As carbene precursors
Diazo compounds are used as precursors to
carbene
In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms.
The term "carbene" m ...
s, which are generated by
thermolysis
Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is re ...
or
photolysis
Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...
, for example in the
Wolff rearrangement. As such they are used in
cyclopropanation for example in the reaction of
ethyl diazoacetate with
styrene.
[Organic Syntheses, Coll. Vol. 6, p.913 (1988); Vol. 50, p.94 (1970]
Link
/ref> Certain diazo compounds can couple to form alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic ...
s in a formal carbene dimerization reaction.
Diazo compounds are intermediates in the Bamford-Stevens reaction of tosylhydrazones to alkenes, again with a carbene intermediate:
:
In the Doyle-Kirmse reaction certain diazo compounds react with allyl sulfides to the homoallyl sulfide. Intramolecular reactions of diazocarbonyl compounds provide access to cyclopropanes. In the Buchner ring expansion diazo compounds react with aromatic rings with ring-expansion.
As nucleophile
The Buchner-Curtius-Schlotterbeck reaction yields ketones from aldehydes and aliphatic diazo compounds:
:
The reaction type is nucleophilic addition
In organic chemistry, a nucleophilic addition reaction is an addition reaction where a chemical compound with an electrophilic double or triple bond reacts with a nucleophile, such that the double or triple bond is broken. Nucleophilic additions d ...
.
Occurrence in nature
Two families of naturally occurring products feature the diazo group: kinamycin and lomaiviticin. These molecules are DNA-intercalators, with diazo functionality as their "warheads". Loss of N2, induced reductively, generates a DNA-cleaving fluorenyl radical.
See also
* Azo compound
* Diazoalkane 1,3-dipolar cycloaddition
* Diazonium compound
Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide.
General propert ...
* Reprography
Reprography (a portmanteau of ''reproduction'' and ''photography'') is the reproduction of graphics through mechanical or electrical means, such as photography or xerography. Reprography is commonly used in catalogs and archives, as well as in ...
* Whiteprint
Whiteprint describes a document reproduction produced by using the diazo chemical process. It is also known as the blue-line process since the result is blue lines on a white background. It is a contact printing process which accurately reproduc ...
References
{{Authority control
Functional groups