Azide
Overview
 
Azide is the anion with the formula N3. It is the conjugate base of hydrazoic acid
Hydrazoic acid
Hydrazoic acid, also known as hydrogen azide or azoimide, is a colorless, volatile, and extremely explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, having chemical formula HN3. It was first isolated in 1890 by Theodor Curtius...

. N3 is a linear anion that is isoelectronic with CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and N2O
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...

. Per valence bond theory
Valence bond theory
In chemistry, valence bond theory is one of two basic theories, along with molecular orbital theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds...

, azide can be described by several resonance structures, an important one being N=N+=N. Azide is also a functional group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

 in organic chemistry
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...

, RN3.

Sodium azide
Sodium azide
Sodium azide is the inorganic compound with the formula NaN3. This colourless azide salt is the gas-forming component in many car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance and is highly soluble in water. It is extremely...

 is found in automobile air bags; it decomposes on heating to give nitrogen gas, which is used to quickly expand the air bag.
Encyclopedia
Azide is the anion with the formula N3. It is the conjugate base of hydrazoic acid
Hydrazoic acid
Hydrazoic acid, also known as hydrogen azide or azoimide, is a colorless, volatile, and extremely explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, having chemical formula HN3. It was first isolated in 1890 by Theodor Curtius...

. N3 is a linear anion that is isoelectronic with CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and N2O
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...

. Per valence bond theory
Valence bond theory
In chemistry, valence bond theory is one of two basic theories, along with molecular orbital theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds...

, azide can be described by several resonance structures, an important one being N=N+=N. Azide is also a functional group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

 in organic chemistry
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...

, RN3.

Sodium azide
Sodium azide
Sodium azide is the inorganic compound with the formula NaN3. This colourless azide salt is the gas-forming component in many car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance and is highly soluble in water. It is extremely...

 is found in automobile air bags; it decomposes on heating to give nitrogen gas, which is used to quickly expand the air bag. The antiviral drug zidovudine
Zidovudine
Zidovudine or azidothymidine is a nucleoside analog reverse-transcriptase inhibitor , a type of antiretroviral drug used for the treatment of HIV/AIDS. It is an analog of thymidine....

 (AZT) contains an azido group. Some azides are valuable as bioorthogonal chemical reporters.

In organic chemistry, azides are commonly used as a way to introduce an amine group. They are also popular for their participation in the "click reaction", and Staudinger ligation. These two reactions are generally quite reliable, lending themselves to combinatorial chemistry
Combinatorial chemistry
Combinatorial chemistry involves the rapid synthesis or the computer simulation of a large number of different but structurally related molecules or materials...

. That aside, low-molecular weight azides tend to be unstable, hence the need for caution.

Preparation

The principal source of the azide moiety is sodium azide
Sodium azide
Sodium azide is the inorganic compound with the formula NaN3. This colourless azide salt is the gas-forming component in many car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance and is highly soluble in water. It is extremely...

. Sodium azide is made industrially by the reaction of nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...

, N2O with sodium amide
Sodium amide
Sodium amide, commonly called sodamide, is the chemical compound with the formula NaNH2. This solid, which is dangerously reactive toward water, is white when pure, but commercial samples are typically gray due to the presence of small quantities of metallic iron from the manufacturing process...

, NaNH2, in liquid ammonia as solvent. The overall stoichiometry is given by
N2O + 2NaNH2 → NaN3 + NaOH + NH3


Most inorganic and organic azides are prepared directly or indirectly from sodium azide. For example, lead azide, used in detonator
Detonator
A detonator is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the latter two being the most common....

s, may be prepared from the metathesis reaction between lead nitrate and sodium azide. As a pseudohalogen
Pseudohalogen
Pseudo'halogen molecules are inorganic molecules of the general formsPs–Ps or Ps–X, where Ps is a pseudohalogen group such as cyanide, cyanate, thiocyanate and others, and X is a "true" halogen...

 compound, sodium azide generally displaces an appropriate leaving group (e.g. Br, I, OTs) to give the azido compound.

Aryl azides may be prepared by displacement of the appropriate diazonium salt with sodium azide, or trimethylsilyl azide
Trimethylsilyl azide
Trimethylsilyl azide is a chemical compound used as a reagent in organic chemistry.-Preparation:Trimethylsilyl azide is commercially available. It may be prepared by the reaction of trimethylsilyl chloride and sodium azide:-Applications:...

; nucleophilic aromatic substitution
Nucleophilic aromatic substitution
right|300px|Aromatic nucleophilic substitutionA nucleophilic aromatic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide, on an aromatic ring...

 is also possible, even with chlorides. Anilines and aromatic hydrazines undergo diazotization, as do alkyl amines and hydrazines.

Appropriately functionalized aliphatic compounds undergo nucleophilic substitution with sodium azide. Aliphatic alcohols give azides via a variant of the Mitsunobu reaction
Mitsunobu reaction
The Mitsunobu reaction is an organic reaction that converts an alcohol into a variety of functional groups, such as an ester, using triphenylphosphine and an azodicarboxylate such as diethyl azodicarboxylate or diisopropyl azodicarboxylate . The alcohol undergoes an inversion of stereochemistry...

, with the use of hydrazoic acid
Hydrazoic acid
Hydrazoic acid, also known as hydrogen azide or azoimide, is a colorless, volatile, and extremely explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, having chemical formula HN3. It was first isolated in 1890 by Theodor Curtius...

. Hydrazines may also form azides by reaction with sodium nitrite
Sodium nitrite
Sodium nitrite is the inorganic compound with the chemical formula NaNO2. It is a white to slight yellowish crystalline powder that is very soluble in water and is hygroscopic...

:
PhNHNH2PhN3
Phenyl azide
Phenylazide is an organic compound with the formula C6H5N3. It is one of the prototypical organic azides. It has a pungent odor. The structure consists of a linear azide substituent bound to a phenyl group...



Alkyl or aryl acyl chloride
Acyl chloride
In organic chemistry, an acyl chloride is an organic compound with the functional group -CO-Cl. Their formula is usually written RCOCl, where R is a side chain. They are usually considered to be reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride,...

s react with sodium azide
Sodium azide
Sodium azide is the inorganic compound with the formula NaN3. This colourless azide salt is the gas-forming component in many car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance and is highly soluble in water. It is extremely...

 in aqueous solution to give acyl azides, which give isocyanates in the Curtius rearrangement
Curtius rearrangement
The Curtius rearrangement , as first defined by Theodor Curtius, is a chemical reaction that involves the rearrangement of an acyl azide to an isocyanate. Several reviews have been published....

.


The azo-transfer compounds, trifluoromethanesulfonyl azide
Trifluoromethanesulfonyl azide
Trifluoromethanesulfonyl azide or triflyl azide is an organic azide used as a reagent in organic synthesis.-Preparation:Trifluoromethanesulfonyl azide is not commercially available. It is prepared before use by reacting trifluoromethanesulfonic anhydride with sodium azide, traditionally in...

 and imidazole-1-sulfonyl azide
Imidazole-1-sulfonyl azide
Imidazole-1-sulfonyl azide is an organic azide compound that can be used as an alternative to trifluoromethanesulfonyl azide. It is a colorless liquid; it may also be used as a better-handled hydrochloride salt.-Preparation:...

, are prepared from sodium azide as well. They react with amines to give the corresponding azides:
RNH2 → RN3

Dutt-Wormall reaction

A classic method for the synthesis of azides is the Dutt-Wormall reaction in which a diazonium salt reacts with a sulfonamide
Sulfonamide (chemistry)
In chemistry, the sulfonamide functional group is -S2-NH2, a sulfonyl group connected to an amine group.A sulfonamide is a compound that contains this group. The general formula is RSO2NH2, where R is some organic group. For example, "methanesulfonamide" is CH3SO2NH2...

 first to a diazoaminosulfinate and then on hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

  the azide and a sulfinic acid.

Inorganic azides

Most azide salts decompose violently to give nitrogen gas, for example with the sodium and silver azide
Silver azide
Silver azide is the chemical compound with the formula AgN3. This colorless solid is a well-known explosive.-Structure and chemistry:Silver azide can be prepared by treating an aqueous solution of silver nitrate with sodium azide...

s:
2 NaN3 → 2 Na + 3 N2
2 AgN3 → 2 Ag + 3 N2


They also liberate toxic hydrazoic acid
Hydrazoic acid
Hydrazoic acid, also known as hydrogen azide or azoimide, is a colorless, volatile, and extremely explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, having chemical formula HN3. It was first isolated in 1890 by Theodor Curtius...

 in the presence of strong acids:
H+ + N3 → HN3


Azide salts may react with heavy metals or heavy metal compounds to give the corresponding azides, which are more sensitive than sodium azide alone. They decompose with sodium nitrite when acidified. This is a method of destroying residual azides, prior to disposal.
2 NaN3 + 2 HNO2 → 3 N2 + 2 NO + 2 NaOH


Many inorganic covalent azides, e.g. chlorine, bromine, and iodine azides, have been described as well.

The azide anion behaves as a nucleophile; it undergoes nucleophilic substitution
Nucleophilic substitution
In organic and inorganic chemistry, nucleophilic substitution is a fundamental class of reactions in which an electron nucleophile selectively bonds with or attacks the positive or partially positive charge of an atom or a group of atoms called the leaving group; the positive or partially positive...

 for both aliphatic and aromatic systems. It reacts with epoxides, causing a ring-opening; it undergoes Michael-like conjugate addition to 1,4-unsaturated carbonyl compounds.

Organic azides

Organic azides engage in useful organic reactions
Organic Reactions
Organic Reactions is a secondary reference which synthesizes the organic chemistry literature around particular chemical transformations. Each chapter of Organic Reactions is devoted to a particular organic chemical reaction, and chapters provide exhaustive coverage of literature work in the form...

. The terminal nitrogen is mildly nucleophilic. Azides easily extrude diatomic nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, a tendency that is exploited in many reactions such as the Staudinger ligation or the Curtius rearrangement
Curtius rearrangement
The Curtius rearrangement , as first defined by Theodor Curtius, is a chemical reaction that involves the rearrangement of an acyl azide to an isocyanate. Several reviews have been published....

 or for example in the synthesis of γ-imino-β-enamino esters.


Azides may be reduced to amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

s by hydrogenolysis
Hydrogenolysis
Hydrogenolysis is a chemical reaction whereby a carbon–carbon or carbon–heteroatom single bond is cleaved or undergoes "lysis" by hydrogen. The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A related reaction is hydrogenation, where hydrogen is added to the molecule, without...

 or with a phosphine, e.g. triphenylphosphine
Triphenylphosphine
Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...

, in the Staudinger reaction
Staudinger reaction
The Staudinger reaction or Staudinger reduction is a chemical reaction in which the combination of an azide with a phosphine or phosphite produces an iminophosphorane intermediate. Combined with the hydrolysis of the aza-ylide to produce a phosphine oxide and an amine, this reaction is a mild...

. This reaction allows azides to serve as protected -NH2 synthons:
RN3 → RNH2


In the azide alkyne Huisgen cycloaddition
Azide alkyne Huisgen cycloaddition
The Azide-Alkyne Huisgen Cycloaddition is a 1,3-dipolar cycloaddition between an azide and a terminal or internal alkyne to give a 1,2,3-triazole. Rolf Huisgen was the first to understand the scope of this organic reaction. American chemist K...

, organic azides react as 1,3-dipole
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...

s, reacting with alkyne
Alkyne
Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...

s to give substituted 1,2,3-triazoles
1,2,3-Triazole
1,2,3-Triazole is one of a pair of isomeric chemical compounds with molecular formula C2H3N3, called triazoles, which have a five-membered ring of two carbon atoms and three nitrogen atoms...

. This reaction is very popular in click chemistry
Click chemistry
Click chemistry is a chemical philosophy introduced by K. Barry Sharpless of The Scripps Research Institute, in 2001 and describes chemistry tailored to generate substances quickly and reliably by joining small units together...

.

Another azide regular is tosyl azide
Tosyl azide
Tosyl azide is a reagent used in organic synthesis.-Uses:Tosyl azide is used for the introduction of azide and diazo functional groups. It is also used as a nitrene source and as a substrate for [3+2] cycloaddition reactions.-Preparation:...

 here in reaction with norbornadiene
Norbornadiene
Norbornadiene is an organic compound. This bicyclic hydrocarbon is the most stable diolefin derived from the norbornane and norbornene. Norbornadiene is primarily of interest as a ligand in homogeneous catalysis, but it has been heavily studied due to its high reactivity and distinctive...

 in a nitrogen insertion reaction:

Azides in coordination chemistry

Azides can be used as sources of the nitrido function in the coordination chemistry of late transition metals, loss of N2 from terminal azide complexes can thus facilitate the formation of unusual oxidation states (see high-valent iron).

Safety

  • Azides are explosophore
    Explosophore
    Explosophores are functional groups in organic chemistry that give organic compounds explosive properties. The term was first coined by Russian chemist V. Pletz in 1935. and originally mistranslated in some articles as "plosophore"...

    s and toxins. Example: tetraazidomethane
    Tetraazidomethane
    Tetraazidomethane is a colorless, highly explosive liquid. Its chemical structure consists of a carbon atom substituted with four azide functional groups.-Synthesis:...

    .
  • Sodium azide
    Sodium azide
    Sodium azide is the inorganic compound with the formula NaN3. This colourless azide salt is the gas-forming component in many car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance and is highly soluble in water. It is extremely...

     is toxic ( oral (rat) = 27 mg/kg) and can be absorbed through the skin. It decomposes explosively upon heating to above 275 °C and reacts vigorously with CS2
    Carbon disulfide
    Carbon disulfide is a colorless volatile liquid with the formula CS2. The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non-polar solvent...

    , bromine
    Bromine
    Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

    , nitric acid
    Nitric acid
    Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

    , dimethyl sulfate
    Dimethyl sulfate
    Dimethyl sulfate is a chemical compound with formula 2SO2. As the diester of methanol and sulfuric acid, its formula is often written as 2SO4 or even Me2SO4, where CH3 or Me is methyl...

    , and a series of heavy metals, including copper
    Copper
    Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

     and lead
    Lead
    Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

    . In reaction with water or Brønsted acids the highly toxic and explosive hydrogen azide
    Hydrazoic acid
    Hydrazoic acid, also known as hydrogen azide or azoimide, is a colorless, volatile, and extremely explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, having chemical formula HN3. It was first isolated in 1890 by Theodor Curtius...

     is released.
  • Heavy metal
    Heavy metals
    A heavy metal is a member of a loosely-defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight,...

     azides, such as lead azide are primary high explosives detonable
    Detonation
    Detonation involves a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations are observed in both conventional solid and liquid explosives, as well as in reactive gases...

     when heated or shaken. Heavy-metal azides are formed when solutions of sodium azide or HN3 vapors come into contact with heavy metals or their salts. Heavy-metal azides can accumulate under certain circumstances, for example, in metal pipelines and on the metal components of diverse equipment (rotary evaporator
    Rotary evaporator
    A rotary evaporator is a device used in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation...

    s, freezedrying
    Freeze drying
    Freeze-drying is a dehydration process typically used to preserve a perishable material or make the material more convenient for transport...

     equipment, cooling traps, water baths, waste pipes), and thus lead to violent explosions.
  • Some organic and other covalent azides are classified as highly explosive and toxic (inorganic azides as neurotoxins; azide ions as cytochrome c oxidase
    Cytochrome c oxidase
    The enzyme cytochrome c oxidase or Complex IV is a large transmembrane protein complex found in bacteria and the mitochondrion.It is the last enzyme in the respiratory electron transport chain of mitochondria located in the mitochondrial membrane...

     inhibitors).
  • It has been reported that sodium azide and polymer-bound azide reagents react with dichloromethane
    Dichloromethane
    Dichloromethane is an organic compound with the formula CH2Cl2. This colorless, volatile liquid with a moderately sweet aroma is widely used as a solvent. Although it is not miscible with water, it is miscible with many organic solvents...

     and chloroform
    Chloroform
    Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...

    to form di- and triazidomethane resp., which are both unstable in high concentrations in solution. Various devastating explosions were reported while reaction mixtures were being concentrated on a rotary evaporator. The hazards of diazidomethane (and triazidomethane) have been well documented.
  • Solid iodoazide is explosive and should not be prepared in the absence of solvent.

External links

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