organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...

, the diazo group is an organic

moiety Moiety may refer to: __NOTOC__ Anthropology * Moiety (kinship), either of two groups into which a society is divided ** A division of society in the Iroquois societal structure in North America ** An Australian Aboriginal kinship group ** Native Ha ...

consisting of two linked

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

atoms at the terminal position. Overall charge-neutral

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

s containing the diazo group bound to a

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

atom are called diazo compounds or diazoalkanes and are described by the general

structural formula The structural formula of a chemical compound is a graphic representation of the molecular structure (determined by structural chemistry methods), showing how the atoms are connected to one another. The chemical bonding within the molecule is al ...

. The simplest example of a diazo compound is

diazomethane Diazomethane is an organic chemical compound with the formula CH2N2, discovered by German chemist Hans von Pechmann in 1894. It is the simplest diazo compound. In the pure form at room temperature, it is an extremely sensitive explosive yellow ga ...

, . Diazo compounds () should not be confused with

azo compound Azo compounds are organic compounds bearing the functional group diazenyl (, in which R and R′ can be either aryl or alkyl groups). IUPAC defines azo compounds as: "Derivatives of diazene (diimide), , wherein both hydrogens are substituted ...

s () 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. The parent, compou ...

s ().

Structure

The

electronic structure Quantum chemistry, also called molecular quantum mechanics, is a branch of physical chemistry focused on the application of quantum mechanics to chemical systems, particularly towards the quantum-mechanical calculation of electronic contributions ...

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 The octet rule is a chemical rule of thumb that reflects the theory that main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The ru ...

-satisfying resonance forms of diazo compounds have formal charges, they are members of a class of compounds known as

1,3-dipole In organic chemistry, a 1,3-dipolar compound or 1,3-dipole is a dipolar compound with delocalized electrons and a separation of charge over three atoms. They are reactants in 1,3-dipolar cycloadditions. The dipole has at least one resonance st ...

s. 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 Ethyl diazoacetate (N=N=CHC(O)OC2H5) is a diazo compound and a reagent in organic chemistry. It was discovered by Theodor Curtius in 1883. The compound can be prepared by reaction of the ethyl ester of glycine with sodium nitrite and sodium aceta ...

(N₂CHCOOEt). A group of isomeric compounds with only few similar properties are the

diazirine In organic chemistry, a diazirine is an organic molecule consisting of a carbon bound to two nitrogen atoms, which are double-bonded to each other, forming a cyclopropene-like ring, 3''H''-diazirine (). Diazirines are isomeric with diazocarbon ...

s, where the carbon and two nitrogens are linked as a ring. Four

resonance structures In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or '' ...

can be drawn: : Diazo resonance structures

Compounds with the diazo moiety should be distinguished from ''

diazonium 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. The parent, compou ...

'' 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 Johann Peter Griess (6 September 1829 – 30 August 1888) was an industrial chemist and an early pioneer of organic chemistry. Griess was influential in the formation of modern dyes, first formulating the diazotization reaction of arylamines. Lif ...

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 or nitrosamines

Alkyl-acyl

nitrosamine Nitrosamines (or more formally ''N''-nitrosamines) are organic compounds produced by industrial processes. The chemical structure is , where R is usually an alkyl group. Nitrosamines have a nitroso group () that are "probable human carcinogens", ...

s in base

dehydrate In physiology, dehydration is a lack of total body water that disrupts Metabolism, metabolic processes. It occurs when free water loss exceeds intake, often resulting from excessive sweating, health conditions, or inadequate consumption of wate ...

to diazo compounds: Diazo Synthesis

Examples are the laboratory synthesis of diazomethane from

diazald Diazald (''N''-methyl-''N''-nitroso-''p''-toluenesulfonamide) is used as a relatively safe and easily handled precursor to diazomethane, which is toxic and unstable. Diazald has become the favored commercially available precursor for the synthesis ...

MNNG Methylnitronitrosoguanidine (MNNG or MNG, NTG when referred to colloquially as nitrosoguanidine) is a biochemical tool used experimentally as a carcinogen and mutagen. It acts by adding alkyl groups to the O6 of guanine and O4 of thymine, which ca ...

. In some cases, the nitrosamine can be produced ''in situ'' without base. Primary aliphatic

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

s R-CH₂-NH₂ with an α acceptor (R = COOR, CN, CHO, COR) in

nitrous acid Nitrous acid (molecular formula ) is a weak and monoprotic acid known only in solution, in the gas phase, and in the form of nitrite () salts. It was discovered by Carl Wilhelm Scheele, who called it " phlogisticated acid of niter". Nitrous ac ...

directly generate a diazo compound.

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 aldehydes. ...

s are

oxidized Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

(

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. At ...

) for example with

silver oxide Silver oxide is the chemical compound with the formula Ag2 O. It is a fine black or dark brown powder that is used to prepare other silver compounds. Preparation Silver oxide can be prepared by combining aqueous solutions of silver nitrate and ...

mercury oxide Mercury oxide can refer to: * Mercury(I) oxide (mercurous oxide), Hg2O * Mercury(II) oxide (mercuric oxide), HgO See also *Montroydite, the mineral form of mercury(II) oxide {{Short pages monitor