diazonium

Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group with the characteristic structure of 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. Historically, diazonium salts have been developed as important intermediates in the organic synthesis of dyes.

Diazonium salt synthesis

The most important method for the preparation of diazonium salts is treatment of aromatic amines such as aniline with sodium nitrite in the presence of a mineral acid. In aqueous solution these salts are unstable at temperatures higher than +5 °C. One can isolate diazonium compounds as the tetrafluoroborate salt, which is stable at room temperature, but typically diazonium compounds are not isolated and once prepared, used immediately in further reactions. The process of forming diazonium compound is called diazotation or diazotization. The reaction was discovered by Peter Griess in 1858, who subsequentely discovered several reactions of the new compound.

Diazonium salt reactions

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, then a solution of the coupler.

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 ammonia and water which forces coupling.

In nanotechnology

In a nanotechnology application of diazonium salts, 4-chlorobenzenediazonium tetrafluoroborate is very efficient in functionalizing single wall nanotubes [2] . 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 15 minutes of grinding 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 reoccurring problem in nanotube technology.

It is also possible to functionalize silicon wafers with diazonium salts forming an aryl monolayer. In one study [3] 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 [4]:

Enlarge picture
Diazonium Salt Application Silicon Wafer


No details on aryl density are given.

Thus far grafting of diazonium salts on metals has been accomplished on iron, cobalt, nickel, platinum, palladium, zinc, copper and gold surfaces. One interesting question raised is the actual positioning on the aryl group on the surface. An in silico study [5] demonstrates that in the period 4 elements 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.

References

1. ^ A Study of the Preparation of Alpha-Pyridyl Halides from Alpha-Aminopyridine by the Diazo Reaction Lyman C. Craig J. Am. Chem. Soc.; 1934; 56(1); 231-232. doi:10.1021/ja01316a072
2. ^ Green Chemical Functionalization of Single-Walled Carbon Nanotubes in Ionic Liquids B. Katherine Price, Jared L. Hudson, and James M. Tour J. Am. Chem. Soc.; 2005; 127(42) pp 14867 - 14870. doi:10.1021/ja053998c
3. ^ Direct Covalent Grafting of Conjugated Molecules onto Si, GaAs, and Pd Surfaces from Aryldiazonium Salts Michael P. Stewart, Francisco Maya, Dmitry V. Kosynkin, Shawn M. Dirk, Joshua J. Stapleton, Christine L. McGuiness, David L. Allara, and James M. Tour J. Am. Chem. Soc.; 2004; 126(1) pp 370 - 378. doi:10.1021/ja0383120
4. ^ Reaction sequence: silicon surface reaction with ammonium hydrogen fluoride creates hydride layer. An electron is transferred from the silicon surface to the diazonium salt in an open circuit potential reduction leaving a silicon radical cation and a diazonium radical. In the next step a proton and a nitrogen molecule are expelled and the two radical residues recombine creating a surface silicon to carbon bond.
5. ^ Structure and Bonding between an Aryl Group and Metal Surfaces De-en Jiang, Bobby G. Sumpter, and Sheng Dai J. Am. Chem. Soc.; 2006; 128(18) pp 6030 - 6031. doi:10.1021/ja061439f

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organic compounds]] An organic compound is any member of a large class of chemical compounds whose molecules contain carbon; for historical reasons discussed below, a few types of compounds such as carbonates, carbon oxides and cyanides, as well as elemental carbon are
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In organic chemistry, functional groups (or moieties) are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those molecules.
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An alkyl is a univalent (or free) radical containing only carbon and hydrogen atoms arranged in a chain. The alkyls form a homologous series with the general formula CnH2n+1.
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aryl refers to any functional group or substituent derived from a simple aromatic ring. There are more specific terms, such as phenyl, to describe unsubstituted aryl groups and subsets of aryl groups (as well as arbitrarily substituted groups: see IUPAC nomenclature), but "aryl" is
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halogens or halogen elements are a series of nonmetal elements from Group 17 (old-style: VII or VIIA; Group 7 IUPAC Style) of the periodic table, comprising fluorine, F; chlorine, Cl; bromine, Br; iodine, I; and astatine, At.
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Organic synthesis is the construction of organic molecules via chemical processes. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has developed into one of the most important aspects of
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dye can generally be described as a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber.
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Aniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. It is the simplest and one of the most imporant aromatic amines, being used as a precursor to more complex chemicals.
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Sodium nitrite, with chemical formula NaNO2, is used as a color fixative and preservative in meats and fish. When pure, it is a white to slight yellowish crystalline powder. It is very soluble in water and is hygroscopic.
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A mineral acid is an acid derived by chemical reaction from inorganic minerals, as opposed to organic acids. Examples include:
  • Hydrochloric acid
  • Nitric acid
  • Phosphoric acid
  • Sulfuric acid
  • Boric acid
  • Hydrofluoric acid

Characteristics


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Johann Peter Griess
Born September 6 1829(1829--)
Kirchhosbach near Waldkappel, Germany
Died July 30 1888 (aged 60)
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An azo coupling is an organic reaction between a diazonium compound and an aniline or a phenol. The reaction product is an azo compound. In this reaction the diazonium salt is an electrophile and the activated arene a nucleophile in an electrophilic aromatic substitution.
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Azo compounds refer to synthetic inorganic chemical compounds bearing the functional group R-N=N-R', in which R and R' can be either aryl or alkyl. The N=N group is called an azo or diimide.
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Electrophilic aromatic substitution or EAS is an organic reaction in which an atom, usually hydrogen, appended to an aromatic system is replaced by an electrophile. The most important reactions of this type that take place are aromatic nitration, aromatic halogenation,
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halogens or halogen elements are a series of nonmetal elements from Group 17 (old-style: VII or VIIA; Group 7 IUPAC Style) of the periodic table, comprising fluorine, F; chlorine, Cl; bromine, Br; iodine, I; and astatine, At.
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A 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.
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The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts.[1][2][3] It is named after the Swiss chemist Traugott Sandmeyer.
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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.
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The Schiemann reaction (also called the Balz-Schiemann reaction) is a chemical reaction in which anilines (1) are transformed to aryl fluorides (3) via diazonium fluoroborates (2).
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Pyridine is a chemical compound with the formula C5H5N. It is a liquid with a distinctively putrid, fishy odour. Pyridine is a simple and fundamentally important heterocyclic aromatic organic compound that is structurally related to benzene, wherein one CH
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Hydrobromic Acid is formed by dissolving the diatomic molecule hydrogen bromide in water. It has a pKa of −9, making it a stronger acid than hydrochloric acid, but not as strong as hydroiodic acid.
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Bromine (IPA: /ˈbroʊmiːn, ˈbroʊmaɪn, ˈbroʊmɪn/, Greek: βρῶμος, brómos, meaning "stench (of he-goats)"
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The Meerwein arylation is an organic reaction involving the addition of an aryl diazonium salt (ArN2X) to an electron-poor alkene usually supported by a metal salt.[1] The reaction product is an alkylated arene compound.
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The Bamberger triazine synthesis in organic chemistry is a classic organic synthesis of a triazine first reported by E. Bamberger in 1892 [1].

The reactants are an aryl diazonium salt obtained from reaction of the corresponding aniline with sodium nitrite and
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Cinnoline is an aromatic heterocyclic compound with the formula C8H6N2 (CAS# [253-66-7]). It is isomeric with phthalazine. Alternative name: benzopyridazine.
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In chemistry, an electrophile (literally electron-lover) is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile.
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Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. It is so named because the spectrum starts with wavelengths slightly shorter than the wavelengths humans identify as the color violet
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Azo compounds refer to synthetic inorganic chemical compounds bearing the functional group R-N=N-R', in which R and R' can be either aryl or alkyl. The N=N group is called an azo or diimide.
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Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of the planet as a precursor to foodstuffs and fertilizers.
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A nanotube is a Nanometer scale wire-like structure that is most often composed of Carbon:
  • Carbon nanotube
Inorganic nanotubes have also been synthesised, including:
  • Boron nitride
  • Silicon
  • Titanium dioxide (B)
  • Tungsten disulphide

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