Diazonium compound
Encyclopedia
Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group
R-N2+ X- where R can be any organic residue such alkyl or aryl
and X is an inorganic or organic anion such as a halogen
. Diazonium salts, especially those where R is an aryl group, are important intermediates in the organic synthesis
of azo dyes.
with nitrous acid
. Usually the nitrous acid is generated in situ (in the same flask) from sodium nitrite
and mineral acid
. In aqueous solution diazonium salts are unstable at temperatures above +5 °C; the -N+≡N group tends to be lost as N2 (nitrogen gas). One can isolate diazonium compounds as tetrafluoroborate
salts, which are stable at room temperature. Often, diazonium compounds are not isolated and once prepared, used immediately in further reactions. This approach is illustrated in the preparation of an arylsulfonyl compound:
It is often preferred that the diazonium salt remain in solutions, but they do tend to supersaturate
. Operators have been killed and injured by an unexpected crystallization of the salt followed by its detonation.
. Dediazotization is commonly induced by halide
s. The process is a formal nucleophilic aromatic substitution
reaction, is the basis of the Sandmeyer Reaction
, the Gomberg-Bachmann reaction
and the Schiemann reaction
. In the so-called Craig method, 2-aminopyridine
reacts with sodium nitrite, hydrobromic acid
and excess bromine
to 2-bromopyridine.
Several other methods exist for dediazotization:
. In this process, the diazonium compound attacks electron-rich arenes such as anilines and phenols concomitant with release of a proton. The process is an example of electrophilic aromatic substitution
:
The resulting azo compound
s are often useful dyes and in fact are called azo dyes. The deep colors of the dyes reflects their extended conjugation
. For example, the dye called aniline yellow
is produced by mixing aniline
and cold solution of diazonium salt and then shaking it vigorously. Aniline yellow is obtained as an yellow solid. Similarly, a cold basic solution of Naphthalen-2-ol
(Β-naphthol) give the intensely orange-red precipitate. Methyl orange
is an example of an azo dye that is used in the laboratory as a pH indicator
.
. Such compounds are usually prepared by direct reaction of the low-valent metal complexes with diazonium salts. Illustrative complexes are [Fe(CO)2(PPh3)2(N2Ph)]+ and the chiral-at-metal complex Fe(CO)(NO)(PPh3)(N2Ph).
, the diazonium salts 4-chlorobenzenediazonium tetrafluoroborate very efficiently functionalizes single wall nanotubes
. In order to exfoliate the nanotubes, they are mixed with an ionic liquid
in a mortar and pestle
. The diazonium salt is added together with potassium carbonate
, and after grinding the mixture at room temperature
the surface of the nanotubes are covered with chlorophenyl groups with an efficiency of 1 in 44 carbon atoms. These added subsituents
prevent the tubes from forming intimate bundles due to large cohesive forces between them, which is a recurring problem in nanotube technology.
It is also possible to functionalize silicon wafers with diazonium salts forming an aryl
monolayer. In one study, the silicon surface is washed with ammonium hydrogen fluoride
leaving it covered with silicon-hydrogen bonds (hydride passivation). The reaction of the surface with a solution of diazonium salt in acetonitrile
for 2 hours in the dark is a spontaneous process through a free radical mechanism
:
So far grafting of diazonium salts on metals has been accomplished on iron
, cobalt
, nickel
, platinum
, palladium
, zinc
, copper
and gold
surfaces. Also the grafting to diamond surfaces has been reported. One interesting question raised is the actual positioning on the aryl group on the surface. An in silico
study demonstrates that in the period 4 element
s from titanium to copper the binding energy
decreases from left to right because the number of d-electrons increases. The metals to the left of iron are positioned tilted towards or flat on the surface favoring metal to carbon pi bond
formation and those on the right of iron are positioned in an upright position, favoring metal to carbon sigma bond
formation. This also explains why diazonium salt grafting thus far has been possible with those metals to right of iron in the periodic table
.
for example is prepared by the thermal decomposition of the phenyldiazonium tetrafluoroborate:
and water which forces coupling.
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...
R-N2+ X- where R can be any organic residue such alkyl or aryl
Aryl
In the context of organic molecules, aryl refers to any functional group or substituent derived from an aromatic ring, be it phenyl, naphthyl, thienyl, indolyl, etc....
and X is an inorganic or organic anion such as a halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
. Diazonium salts, especially those where R is an aryl group, are important intermediates in the organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
of azo dyes.
Preparation
The process of forming diazonium compounds is called "diazotation", "diazoniation", or "diazotization". The reaction was first reported by Peter Griess in 1858, who subsequently discovered several reactions of this new class of compounds. The most important method for the preparation of diazonium salts is treatment of aromatic amines such as anilineAniline
Aniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane...
with nitrous acid
Nitrous acid
Nitrous acid is a weak and monobasic acid known only in solution and in the form of nitrite salts.Nitrous acid is used to make diazides from amines; this occurs by nucleophilic attack of the amine onto the nitrite, reprotonation by the surrounding solvent, and double-elimination of water...
. Usually the nitrous acid is generated in situ (in the same flask) from 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...
and mineral acid
Mineral acid
A mineral acid is an acid derived from one or more inorganic compounds. A mineral acid is not organic and all mineral acids release hydrogen ions when dissolved in water.-Characteristics:...
. In aqueous solution diazonium salts are unstable at temperatures above +5 °C; the -N+≡N group tends to be lost as N2 (nitrogen gas). One can isolate diazonium compounds as tetrafluoroborate
Tetrafluoroborate
Tetrafluoroborate is the anion BF4−. This tetrahedral species is isoelectronic with tetrafluoromethane, CF4 and tetrafluoroammonium NF4+, and is valence isoelectronic with many stable and important species including the closely related anion perchlorate, ClO4−...
salts, which are stable at room temperature. Often, diazonium compounds are not isolated and once prepared, used immediately in further reactions. This approach is illustrated in the preparation of an arylsulfonyl compound:
It is often preferred that the diazonium salt remain in solutions, but they do tend to supersaturate
Supersaturation
The term supersaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances...
. Operators have been killed and injured by an unexpected crystallization of the salt followed by its detonation.
Displacement of N2 group
The diazo group (N2) can be displaced in a process called dediazoniation, which releases nitrogen N2 and an aryl carbocation or more commonly in combination with single electron transfer an aryl radicalAryl radical
An Aryl radical in organic chemistry is an reactive intermediate and an arene compound incorporating one free radical carbon atom as part of the ring structure. As such it is the radical counterpart of the Arenium ion. The parent compound is the phenyl radical C6H5....
. Dediazotization is commonly induced by halide
Halide
A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. Many salts are halides...
s. The process is a formal 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...
reaction, is the basis of the Sandmeyer Reaction
Sandmeyer reaction
The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts. It is named after the Swiss chemist Traugott Sandmeyer....
, the Gomberg-Bachmann reaction
Gomberg-Bachmann reaction
The Gomberg–Bachmann reaction, named for the Ukrainian-American chemist Moses Gomberg and the American chemist Werner Emmanuel Bachmann, is an aryl-aryl coupling reaction via a diazonium salt....
and the Schiemann reaction
Schiemann reaction
The Schiemann reaction is a chemical reaction in which anilines are transformed to aryl fluorides via diazonium fluoroborates...
. In the so-called Craig method, 2-aminopyridine
Pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
reacts with sodium nitrite, hydrobromic acid
Hydrobromic acid
Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at 124.3 °C and contains 47.6% HBr by weight, which is 8.89 mol/L. Hydrobromic acid has a pKa of −9, making it a...
and excess 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...
to 2-bromopyridine.
Several other methods exist for dediazotization:
- by organic reduction at an electrodeElectrosynthesisElectrosynthesis in organic chemistry is the synthesis of chemical compounds in a electrochemical cell The main advantage of electrosynthesis over an ordinary redox reaction is avoidance of the potential wasteful other half-reaction and the ability to precisely tune the required potential...
- by gamma radiation from solvated electronSolvated electronA solvated electron is a free electron in a solution. Solvated electrons occur widely although they are often not observed directly. The deep colour of solutions of alkali metals in ammonia arises form the presence of solvated electrons: blue when dilute and copper-colored when more concentrated...
s generated in water - photoinducedPhotochemistryPhotochemistry, a sub-discipline of chemistry, is the study of chemical reactions that proceed with the absorption of light by atoms or molecules.. Everyday examples include photosynthesis, the degradation of plastics and the formation of vitamin D with sunlight.-Principles:Light is a type of...
electron transfer - reduction by metal cations, most commonly a cuprous salt.
- anion-induced dediazoniation: a counterion such as iodine gives electron transfer to the diazonium cation forming the aryl radical and an iodine radical
- solvent-induced dediazoniation with solventSolventA solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
serving as electron donor
Diazo coupling
An important reaction of aromatic diazonium salts is azo couplingAzo coupling
An azo coupling is an organic reaction between a diazonium compound and a dialkylaniline , phenol or other aromatic compound which produces an azo compound. In this reaction the diazonium salt is an electrophile and the activated arene is a nucleophile in an electrophilic aromatic substitution...
. In this process, the diazonium compound attacks electron-rich arenes such as anilines and phenols concomitant with release of a proton. The process is an example of electrophilic aromatic substitution
Electrophilic aromatic substitution
Electrophilic aromatic substitution EAS is an organic reaction in which an atom, usually hydrogen, appended to an aromatic system is replaced by an electrophile...
:
- ArN2+ + Ar'H → ArN2Ar' + H+
The resulting azo compound
Azo compound
Azo compounds are compounds bearing the functional group R-N=N-R', in which R and R' can be either aryl or alkyl. IUPAC defines azo compounds as: "Derivatives of diazene , HN=NH, wherein both hydrogens are substituted by hydrocarbyl groups, e.g. PhN=NPh azobenzene or diphenyldiazene." The more...
s are often useful dyes and in fact are called azo dyes. The deep colors of the dyes reflects their extended conjugation
Conjugation
Conjugation or conjugate may refer to:* Conjugation , the modification of a verb from its basic form* Conjugate , used to rationalize the denominator of a fraction...
. For example, the dye called aniline yellow
Aniline Yellow
Aniline Yellow is a yellow azo dye and an aromatic amine. It is a derivate of azobenzene. It has the appearance of an orange powder. It is a carcinogen....
is produced by mixing aniline
Aniline
Aniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane...
and cold solution of diazonium salt and then shaking it vigorously. Aniline yellow is obtained as an yellow solid. Similarly, a cold basic solution of Naphthalen-2-ol
2-Naphthol
2-Naphthol, or β-naphthol, is a colorless crystalline solid with the formula C10H7OH. It is an isomer of 1-naphthol, differing by the location of the hydroxyl group on naphthalene. The naphthols are naphthalene homologues of phenol, with the hydroxyl group being more reactive than in the phenols....
(Β-naphthol) give the intensely orange-red precipitate. Methyl orange
Methyl orange
Methyl orange is a pH indicator frequently used in titrations.It is often used in titrations because of its clear and distinct colour change. Because it changes colour at the pH of a mid-strength acid, it is usually used in titrations for acids...
is an example of an azo dye that is used in the laboratory as a pH indicator
PH indicator
A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions or hydrogen ions in the Arrhenius model. Normally, the indicator causes the...
.
Other reactions
- In Meerwein arylationMeerwein arylationThe Meerwein arylation is an organic reaction involving the addition of an aryl diazonium salt to an electron-poor alkene usually supported by a metal salt. The reaction product is an alkylated arene compound...
the salt also decomposes and the aryl residue reacts with an electron deficient alkene in an addition reaction - In the Bamberger triazine synthesisBamberger triazine synthesisThe Bamberger triazine synthesis in organic chemistry is a classic organic synthesis of a triazine first reported by Eugen Bamberger in 1892 ....
and the Widman-Stoermer synthesis a diazonium salt reacts as an electrophileElectrophileIn general electrophiles are positively charged species that are attracted to an electron rich centre. In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile...
through its terminal nitrogen atom with an activated double bond. - HydrolysisHydrolysisHydrolysis 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...
of diazonium salts yields alcoholAlcoholIn chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s - Reduction with hypophosphorous acidHypophosphorous acidHypophosphorous acid is a phosphorus oxoacid and a powerful reducing agent with molecular formula H3PO2. Inorganic chemists refer to the free acid by this name , or the acceptable name of phosphinic acid. It is a colorless low-melting compound, which is soluble in water, dioxane, and alcohols...
replaces the nitrogen by hydrogen, which allows amino (and, indirectly, nitro groups) to be removed - In the Heck-Matsuda ReactionHeck-Matsuda reactionThe Heck-Matsuda reaction is an organic reaction and a type of palladium catalysed arylation of olefins that uses arenediazonium salts as an alternative to aryl halides and triflates...
the salt couples with an alkene.
Metal complexes
Diazonium cations are similar to NO+ and thus form complexes with many metal centers, especially in organometallic chemistryOrganometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
. Such compounds are usually prepared by direct reaction of the low-valent metal complexes with diazonium salts. Illustrative complexes are [Fe(CO)2(PPh3)2(N2Ph)]+ and the chiral-at-metal complex Fe(CO)(NO)(PPh3)(N2Ph).
Grafting reactions
In a potential application in nanotechnologyNanotechnology
Nanotechnology is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres...
, the diazonium salts 4-chlorobenzenediazonium tetrafluoroborate very efficiently functionalizes single wall nanotubes
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
. In order to exfoliate the nanotubes, they are mixed with an ionic liquid
Ionic liquid
An ionic liquid is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below some arbitrary temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of electrically neutral molecules, ILs are largely made...
in a mortar and pestle
Mortar and pestle
A mortar and pestle is a tool used to crush, grind, and mix solid substances . The pestle is a heavy bat-shaped object, the end of which is used for crushing and grinding. The mortar is a bowl, typically made of hard wood, ceramic or stone...
. The diazonium salt is added together with potassium carbonate
Potassium carbonate
Potassium carbonate is a white salt, soluble in water , which forms a strongly alkaline solution. It can be made as the product of potassium hydroxide's absorbent reaction with carbon dioxide. It is deliquescent, often appearing a damp or wet solid...
, and after grinding the mixture at room temperature
Room temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...
the surface of the nanotubes are covered with chlorophenyl groups with an efficiency of 1 in 44 carbon atoms. These added subsituents
Substituent
In organic chemistry and biochemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon...
prevent the tubes from forming intimate bundles due to large cohesive forces between them, which is a recurring problem in nanotube technology.
It is also possible to functionalize silicon wafers with diazonium salts forming an aryl
Aryl
In the context of organic molecules, aryl refers to any functional group or substituent derived from an aromatic ring, be it phenyl, naphthyl, thienyl, indolyl, etc....
monolayer. In one study, the silicon surface is washed with ammonium hydrogen fluoride
Ammonium hydrogen fluoride
Ammonium hydrogen fluoride is the inorganic compound with the formula NH4HF2 or NH4F·HF. It is produced from ammonia and hydrogen fluoride. This colourless salt is a glass-etchant and an intermediate in a once-contemplated route to hydrofluoric acid....
leaving it covered with silicon-hydrogen bonds (hydride passivation). The reaction of the surface with a solution of diazonium salt in acetonitrile
Acetonitrile
Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...
for 2 hours in the dark is a spontaneous process through a free radical mechanism
Reaction mechanism
In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs.Although only the net chemical change is directly observable for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in...
:
So far grafting of diazonium salts on metals has been accomplished on iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
, nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
, palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...
, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, 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 gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
surfaces. Also the grafting to diamond surfaces has been reported. One interesting question raised is the actual positioning on the aryl group on the surface. An in silico
In silico
In silico is an expression used to mean "performed on computer or via computer simulation." The phrase was coined in 1989 as an analogy to the Latin phrases in vivo and in vitro which are commonly used in biology and refer to experiments done in living organisms and outside of living organisms,...
study demonstrates that in the period 4 element
Period 4 element
A period 4 element is one of the chemical elements in the fourth row of the periodic table of the elements. The periodic table is laid out in rows to illustrate recurring trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour...
s from titanium to copper the binding energy
Binding energy
Binding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than its constituent parts; this is what keeps the system together—often this means that energy is released upon the creation of a bound state...
decreases from left to right because the number of d-electrons increases. The metals to the left of iron are positioned tilted towards or flat on the surface favoring metal to carbon pi bond
Pi bond
In chemistry, pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital...
formation and those on the right of iron are positioned in an upright position, favoring metal to carbon sigma bond
Sigma bond
In chemistry, sigma bonds are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most clearly defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is...
formation. This also explains why diazonium salt grafting thus far has been possible with those metals to right of iron in the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
.
Applications
The first use of diazonium salts was to produce water-fast dyed fabrics by immersing the fabric in an aqueous solution of the diazonium compound, followed by immersion in a solution of the coupler (the electron-rich ring that undergoes electrophilic substitution). The major current use remains in the dye industry.Organic synthesis
As discussed above under reactions, diazonium compounds are useful in the preparation of substituted aromatic compounds from anilines. FluorobenzeneFluorobenzene
Fluorobenzene is the chemical compound with the formula C6H5F, often abbreviated PhF. This species is a derivative of benzene, with a single fluorine atom attached. Its melting point is 44 °C lower than that of benzene, indicative of the remarkable effect of fluorination on the intermolecular...
for example is prepared by the thermal decomposition of the phenyldiazonium tetrafluoroborate:
- PhN2BF4 → PhF + BF3Boron trifluorideBoron trifluoride is the chemical compound with the formula BF3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...
+ N2NitrogenNitrogen 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...
Niche uses
Diazonium salts are light sensitive and break down under near UV or violet light. This property has led to their use in document reproduction. In this process, paper or film is coated with a diazonium salt. After contact exposure under light, the residual diazo is converted to a stable azo dye with an aqueous solution of coupler. A more common process uses a paper coated with diazo, coupler and an acid to inhibit coupling; after exposure the image is developed by a vapor mixture of ammoniaAmmonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
and water which forces coupling.