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14-September-2008 18:38:49 - Diazonium compound Redirected from Diazonium salt Phenyldiazonium cation Phenyldiazonium cation 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. Contents 1 Diazonium salt synthesis 2 Diazonium salt reactions 3 Applications 4 In nanotechnology 5 See also 6 References 7 External links 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; the N+triple bond N group tends to be lost as N2, i.e. nitrogen gas. 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 azo compounds azo dyes in electrophilic aromatic substitution. Nitrogen replacement reactions by halogens take place in nucleophilic aromatic substitution such as 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 1. In Meerwein arylation the salt also decomposes and the aryl residue reacts with an electron deficient alkene in an addition reaction In the Bamberger triazine synthesis and the Widman-Stoermer synthesis a diazonium salt reacts as an electrophile through its terminal nitrogen atom with an activated double bond. Hydrolysis of diazonium salts yields alcohols Reduction with hypophosphorous acid replaces the nitrogen by hydrogen, which allows amino and nitro groups to be removed easily from rings 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: 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. See also Diazo 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; 561; 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; 12742 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; 1261 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; 12818 pp 6030 - 6031. doi:10.1021/ja061439f External links W. Reusch. Reactions of Amines. VirtualText of Organic CHemistry. Michigan State Uniersity. Retrieved from http://en..org/wiki/Diazonium_compound Categories: Functional groups | Carbon-heteroatom bond forming reactions Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages ÄŒesky Deutsch Español Français Nederlands 日本語 Polski Português SlovenÄ?ina ä¸æ–‡ This page was last modified on 9 August 2008, at 00:28
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