Diazonium compound 2531152 224503158 2008-07-09T03:42:46Z Puppy8800 5404759 iw [[Image:Diazonium.png|thumb|right|Phenyldiazonium cation]] '''Diazonium compounds''' or '''diazonium salts''' are a group of [[organic compounds]] sharing a common [[functional group]] with the characteristic structure of R-N<sub>2</sub><sup>+</sup> X<sup>-</sup> 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 [[dye]]s. == 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<sup>+</sup>triple bond N group tends to be lost as N<sub>2</sub>, 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 compound]]s (azo dyes) in [[electrophilic aromatic substitution]]. * Nitrogen replacement reactions by [[halogen]]s 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''', [[pyridine|2-aminopyridine]] reacts with sodium nitrite, [[hydrobromic acid]] and excess [[bromine]] to 2-bromopyridine <ref>''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}}</ref>. * 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 [[alcohol]]s * 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 [[nanotube|single wall nanotubes]] <ref> 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}}</ref> . In order to [[exfoliation (material science)|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 [[substituent|subsituents]] prevent the tubes from forming intimate bundles due to large [[cohesive force]]s between them which is a reoccurring problem in nanotube technology. It is also possible to functionalize [[silicon wafer]]s with diazonium salts forming an [[aryl]] monolayer. In one study <ref>''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}}</ref> 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]] [[reaction mechanism|mechanism]] <ref>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. </ref>: [[Image:DiazoniumSaltApplicationSiliconWafer.png|center|600px|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 <ref>''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}} </ref> 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]]. ==See also== *[[Diazo]] == References == <references/> == External links == * {{cite web | publisher = [[Michigan State Uniersity]] | author = W. Reusch | work = VirtualText of Organic CHemistry | title = Reactions of Amines | url = http://www.cem.msu.edu/~reusch/VirtualText/amine2.htm}} [[Category:functional groups]] [[Category:Carbon-heteroatom bond forming reactions]] [[cs:Diazoniové soli]] [[de:Diazoniumsalze]] [[es:Sal de diazonio]] [[fr:Diazonium]] [[nl:Diazoniumverbinding]] [[ja:ジアゾニウム化合物]] [[pl:Sól diazoniowa]] [[pt:Sal de diazônio]] [[sk:Diazóniová soľ]] [[zh:重氮盐]]