Diazonium compound

Diazonium compounds or diazonium salts are a group of dyes.

Diazonium salt synthesis

The most important method for the preparation of diazonium salts is treatment of aromatic amines such as 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' (diazoniation) or diazotisation GB or diazotization US. The reaction was discovered by Peter Griess in 1858, who subsequentely discovered several reactions of the new compound.

Diazonium salt reactions

The most important aromatic diazonium salt reactions are azo coupling with anilines and phenols to electrophilic aromatic substitution.
Nitrogen replacement reactions by bromine to 2-bromopyridine ^[1].
In Meerwein arylation the salt also decomposes and the aryl residue reacts with an electron deficient alkene in an addition reaction
In the electrophile through its terminal nitrogen atom with an activated double bond.
Hydrolysis of diazonium salts yields alcohols

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 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 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 mechanism ^[4]:

No details on aryl density are given.

Thus far grafting of diazonium salts on metals has been accomplished on periodic table.

References

^ 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
^ 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
^ 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
^ 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.
^ 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