:Diazonium compound

According to X-ray crystallography the {{chem2|C\sN+\tN}} linkage is linear in typical diazonium salts. The {{chem2|N+\tN}} bond distance in benzenediazonium tetrafluoroborate is 1.083(3) Å,{{cite journal|doi=10.1139/v82-407|title=The Crystal Structure of Benzenediazonium Tetrafluoroborate, C₆H₅N₂⁺•BF₄⁻1|year=1982|last1=Cygler|first1=Miroslaw|last2=Przybylska|first2=Maria|last3=Elofson|first3=Richard Macleod|journal=Canadian Journal of Chemistry|volume=60|issue=22|pages=2852–2855|doi-access=free}} which is almost identical to that for dinitrogen molecule (N≡N).

The linear free energy constants σ_m and σ_p indicate that the diazonium group is strongly electron-withdrawing. Thus, the diazonio-substituted phenols and benzoic acids have greatly reduced pK_a values compared to their unsubstituted counterparts. The pK_a of phenolic proton of 4-hydroxybenzenediazonium is 3.4,{{Citation|last=D. Bravo-Díaz|first=Carlos|chapter=Diazohydroxides, Diazoethers and Related Species|date=2010-10-15|editor-last=Rappoport|editor-first=Zvi|publisher=John Wiley & Sons, Ltd|language=en|doi=10.1002/9780470682531.pat0511|isbn=9780470682531|title=PATai's Chemistry of Functional Groups}} versus 9.9 for phenol itself. In other words, the diazonium group raises the ionization constant K_a (enhances the acidity) by a million-fold. This also causes arenediazonium salts to have decreased reactivity when electron-donating groups are present on the aromatic ring.{{Cite book |last=裴 |first=坚 |title=基础有机化学 |edition=4th |pages=868–869 |trans-title=Basic Organic Chemistry}}

The stability of arenediazonium salts is highly sensitive to the counterion. Phenyldiazonium chloride is dangerously explosive, but benzenediazonium tetrafluoroborate is easily handled on the bench.{{Citation needed|date=January 2024}}

Alkanediazonium salts are synthetically unimportant due to their extreme and uncontrolled reactivity toward S_N2/S_N1/E1 substitution. These cations are however of theoretical interest. Furthermore, methyldiazonium carboxylate is believed to be an intermediate in the methylation of carboxylic acids by diazomethane, a common transformation.{{Cite journal|last1=Streitwieser|first1=Andrew|last2=Schaeffer|first2=William D.|date=June 1957|title=Stereochemistry of the Primary Carbon. VI. The Reaction of Optically Active 1-Aminobutane-1-d with Nitrous Acid. Mechanism of the Amine-Nitrous Acid Reaction1|journal=Journal of the American Chemical Society|volume=79|issue=11|pages=2888–2893|doi=10.1021/ja01568a054}}{{Cite journal|last1=Friedman|first1=Lester|last2=Jurewicz|first2=Anthony T.|last3=Bayless|first3=John H.|date=March 1969|title=Influence of solvent on diazoalkane-alkanediazonium ion equilibriums in amine deaminations|journal=Journal of the American Chemical Society|volume=91|issue=7|pages=1795–1799|doi=10.1021/ja01035a032}}

File:Diazomethanemethylation.png

Loss of {{chem2|N2}} is both enthalpically and entropically favorable:

:{{chem2|[CH3N2]+ → [CH3]+ + N2}}, ΔH = −43 kcal/mol

:{{chem2|[CH3CH2N2]+ → [CH3CH2]+ + N2}}, ΔH = −11 kcal/mol

For secondary and tertiary alkanediazonium species, the enthalpic change is calculated to be close to zero or negative, with minimal activation barrier. Hence, secondary and (especially) tertiary alkanediazonium species are either unbound, nonexistent species or, at best, extremely fleeting intermediates.{{Cite book|title=Advanced organic chemistry|author=Carey, Francis A.|date=2007|publisher=Springer|others=Sundberg, Richard J.|isbn=9780387448978|edition= 5th|location=New York|oclc=154040953}}

The aqueous pK_a of methyldiazonium ({{chem2|[CH3N2]+}}) is estimated to be <10.{{Cite journal|last1=Fei|first1=Na|last2=Sauter|first2=Basilius|last3=Gillingham|first3=Dennis|date=2016|title=The pK_a of Brønsted acids controls their reactivity with diazo compounds|journal=Chemical Communications|language=en|volume=52|issue=47|pages=7501–7504|doi=10.1039/C6CC03561B|pmid=27212133|doi-access=free}}

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. Most commonly, diazonium salts are prepared by treatment of aromatic amines with nitrous acid and additional acid. Usually the nitrous acid is generated in situ (in the same flask) from sodium nitrite and the excess mineral acid (usually aqueous HCl, {{chem2|H2SO4}}, {{chem2|p\-H3CC6H4SO3H}}, or {{chem2|H[BF4]}}):

:{{chem2|ArNH2 + HNO2 + HX → [ArN2]+X- + 2 H2O}}

File:PhN2BF4.jpg.]]

Chloride salts of diazonium cation, traditionally prepared from the aniline, sodium nitrite, and hydrochloric acid, are unstable at room temperature and are classically prepared at 0 – 5 °C. However, one can isolate diazonium compounds as tetrafluoroborate or tosylate salts,{{Cite journal|last1=Filimonov|first1=Victor D.|last2=Trusova|first2=Marina|last3=Postnikov|first3=Pavel|last4=Krasnokutskaya|first4=Elena A.|last5=Lee|first5=Young Min|last6=Hwang|first6=Ho Yun|last7=Kim|first7=Hyunuk|last8=Chi|first8=Ki-Whan|date=2008-09-18|title=Unusually Stable, Versatile, and Pure Arenediazonium Tosylates: Their Preparation, Structures, and Synthetic Applicability|journal=Organic Letters|language=EN|volume=10|issue=18|pages=3961–3964|doi=10.1021/ol8013528|pmid=18722457|issn=1523-7060}} which are stable solids at room temperature.{{cite journal | author1=Mihelač, M. |author2=Siljanovska, A. |author3=Košmrlj, J. |title=A convenient approach to arenediazonium tosylates |journal=Dyes Pigm. |year=2021 |volume=184 |pages=108726 |doi=10.1016/j.dyepig.2020.108726 |doi-access=free}} It is often preferred that the diazonium salt remain in solution, but they do tend to supersaturate. Operators have been injured or even killed by an unexpected crystallization of the salt followed by its detonation.{{cite web|url=http://www.crhf.org.uk/incident71.html|title=UK CRHF Incident Report – Supersaturated Diazonium salt causes Fatality|publisher=UK Chemical Reaction Hazards Forum|access-date=13 May 2010|archive-url=https://web.archive.org/web/20181006095115/http://www.crhf.org.uk/incident71.html|archive-date=6 October 2018|url-status=dead}}

Due to these hazards, diazonium compounds are often not isolated. Instead they are used in situ. This approach is illustrated in the preparation of an arenesulfonyl compound:{{cite journal |journal=Org. Synth. |author= R. V. Hoffman |title= m-Trifluoromethylbenzenesulfonyl Chloride |volume= 60 |pages= 121 |year= 1981 |doi= 10.15227/orgsyn.060.0121}}

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The first and still main use of diazonium salts is azo coupling, which is exploited in the production of azo dyes.Klaus Hunger, Peter Mischke, Wolfgang Rieper, et al. "Azo Dyes" in Ullmann’s Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a03_245}}.Chemistry of the Diazonium and Diazo Groups: Part 1. S. Patai, Ed. 1978 Wiley-Blackwell. {{ISBN|0-471-99492-8}}. Chemistry of the Diazonium and Diazo Groups: Part 2. S. Patai, Ed. 1978 Wiley-Blackwell. {{ISBN|0-471-99493-6}}. In some cases water-fast dyed fabrics are simply immersed 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). In this process, the diazonium compound is attacked by, i.e., coupled to, electron-rich substrates. When the coupling partners are arenes such as anilines and phenols, the process is an example of electrophilic aromatic substitution:

:{{chem2|[ArN2]+ + Ar'H → ArN2Ar' + H+}}

The deep colors of the dyes reflects their extended conjugation. A popular azo dye is aniline yellow, produced from aniline. Naphthalen-2-ol (beta-naphthol) gives an intensely orange-red dye. Methyl orange is an example of an azo dye that is used in the laboratory as a pH indicator..{{cite web|last=Clark|first=Jim|title=chemguide|url=http://www.chemguide.co.uk/organicprops/aniline/propsdiazo.html|access-date=28 September 2011}}

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Another commercially important class of coupling partners are acetoacetic amides, as illustrated by the preparation of Pigment Yellow 12, a diarylide pigment.K. Hunger. W. Herbst "Pigments, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012. {{doi|10.1002/14356007.a20_371}}

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Arenediazonium cations undergo several reactions in which the {{chem2|N2}} group is replaced by another group or ion.March, J. “Advanced Organic Chemistry” 4th Ed. J. Wiley and Sons, 1992: New York. {{ISBN|978-0-471-60180-7}}.{{cite book | title=Organic Chemistry | publisher=Jones & Bartlett Learning |author1=Marye Anne Fox |author2=James K. Whitesell | year=2004 | pages=535–538 | isbn=978-0-7637-2197-8 | url=https://books.google.com/books?id=xx_uIP5LgO8C&q=Reactions+of+Benzenediazonium+chloride&pg=PA536 | edition= 3, illustrated}}

{{main|Sandmeyer reaction}}

Benzenediazonium chloride heated with cuprous chloride or cuprous bromide respectively dissolved in HCl or HBr yield chlorobenzene or bromobenzene, respectively.

:{{chem2|[C6H5N2]+ + CuCl → C6H5Cl + N2 + Cu+}}

In the Gattermann reaction (there are other "Gattermann reactions"), benzenediazonium chloride is warmed with copper powder and HCl or HBr to produce chlorobenzene and bromobenzene respectively.{{cite journal |author= L. Gattermann |title= Untersuchungen über Diazoverbindungen |journal= Berichte der Deutschen Chemischen Gesellschaft |year= 1894 |volume= 23

|issue= 1 |pages= 1218–1228 |doi= 10.1002/cber.189002301199 |url= http://gallica.bnf.fr/ark:/12148/bpt6k90720c/f1220.chemindefer}}

:{{chem2|2 Cu + 2 [C6H5N2]+ → 2 Cu+ + (C6H5)2 + 2 N2 (initiation)}}

:{{chem2|[C6H5N2]+ + HX → C6H5X + N2 + H+ (Cu+ catalysis)}}

Arenediazonium cations react with potassium iodide to give the aryl iodide:{{cite journal |doi=10.15227/orgsyn.019.0055|first1=H. J.|last1=Lucas|first2=E. R.|last2=Kennedy |title=Iodobenzene |journal=Org. Synth. |year=1939|volume=19|page=55}}

:{{chem2|[C6H5N2]+ + KI → C6H5I + K+ + N2}}

{{main|Balz–Schiemann reaction}}

Fluorobenzene is produced by thermal decomposition of benzenediazonium tetrafluoroborate. The conversion is called the Balz–Schiemann reaction.{{cite journal |journal=Org. Synth. |author= Flood, D. T. |year= 1933 |title= Fluorobenzene |volume= 13 |pages= 46 |doi= 10.15227/orgsyn.013.0046}}.

:{{chem2|[C6H5N2]+[BF4]- → C6H5F + BF3 + N2}}

The traditional Balz–Schiemann reaction has been the subject of many motivations, e.g. using hexafluorophosphate(V) ({{chem2|[PF6]-}}) and hexafluoroantimonate(V) ({{chem2|[SbF6]-}}) in place of tetrafluoroborate ({{chem2|[BF4]-}}). The diazotization can be effected with nitrosonium salts such as nitrosonium hexafluoroantimonate(V) {{chem2|[NO]+[SbF6]-}}.{{cite journal|journal=Synthesis|year=2010|pages=1804–1821|doi=10.1055/s-0029-1218742|title=C–F Bond Formation for the Synthesis of Aryl Fluorides|first1=Takeru|last1=Furuya|first2=Johannes E. M. N.|last2=Klein|first3=Tobias|last3=Ritter|pmc=2953275|pmid=20953341|volume=2010|issue=11}}

A pair of diazonium cations can be coupled to give biaryls. This conversion is illustrated by the coupling of the diazonium salt derived from anthranilic acid to give diphenic acid ({{chem2|(C6H4CO2H)2}}).{{cite journal|doi=10.15227/orgsyn.007.0030|first1=E. R.|last1=Atkinson|first2=H. J.|last2=Lawler|title=Diphenic Acid |journal=Org. Synth. |volume=7|pages=30|year=1927}} In a related reaction, the same diazonium salt undergoes loss of {{chem2|N2}} and {{chem2|CO2}} to give benzyne.{{cite journal| last1= Logullo |first1= F. M. |last2= Seitz |first2= A. H. |last3= Friedman |first3= L. | title = Benzenediazonium-2-carboxy- and Biphenylene | page= 12 | volume= 48 | year = 1968| doi= 10.15227/orgsyn.048.0012 | journal= Org. Synth.}}

Arenediazonium cations reduced by hypophosphorous acid,Reinhard Bruckner, ed. Michael Harmata; Organic Mechanisms Reactions, Stereochemistry and Synthesis 3rd Ed, p.246, {{ISBN|978-3-8274-1579-0}} ethanol,{{cite journal|date=1958|title=Mechanisms of Diazonium Salt Reactions. VI. The Reactions of Diazonium Salts with Alcohols under Acidic Conditions; Evidence for Hydride Transfer1|journal=Journal of the American Chemical Society|volume=80|issue=22|pages=6072–6077|doi=10.1021/ja01555a044|last1=DeTarr|first1=D.F.|last2=Kosuge|first2=T.}} sodium stanniteFriedlander, Ber., 1889, 587, 22 or alkaline sodium thiosulphateGrandmougin, Ber., 1907, 40, 858 gives benzene:

:{{chem2|[C6H5N2]+Cl- + H3PO2 + H2O → C6H6 + N2 + H3PO3 + HCl}}

:{{chem2|[C6H5N2]+Cl- + CH3CH2OH → C6H6 + N2 + CH3CHO + HCl}}

:{{chem2|[C6H5N2]+Cl- + NaOH + Na2SnO2 → C6H6 + N2 + Na2SnO3 + NaCl}}

An alternative way suggested by Baeyer & Pfitzinger is to replace the diazo group with H is: first to convert it into hydrazine by treating with {{chem2|SnCl2}} then to oxidize it into hydrocarbon by boiling with cupric sulphate solution.Baeyer & Pfitzinger, Ber., 1885, 18, 90, 786

Phenols are produced by heating aqueous solutions of arenediazonium salts:{{cite journal|author=H. E. Ungnade, E. F. Orwoll|doi=10.15227/orgsyn.023.0011|title=3-Bromo-4-hydroxytoluene|journal=Org. Synth. |volume=23|pages=11|year=1943}}{{Cite journal|date=2017|title=Facile Preparation of Phenol|journal=Synlett|volume=28|issue=13|pages=1641–1645|doi=10.1055/s-0036-1588180|last1=Kazem-Rostami|first1=Masoud|s2cid=99294625 }}{{Cite book|title=Advanced Organic Chemistry|url=https://archive.org/details/advancedorganicc00care_636|url-access=limited|author1=Carey, F. A. |author2=Sundberg, R. J. |publisher=Springer|year=2007|location=Vol. B, Chapter 11|pages=[https://archive.org/details/advancedorganicc00care_636/page/n1051 1028]}}{{Cite journal|doi=10.1002/app.39069|title=Synthesis, characterization, and application of a triazene-based polysulfone as a dye adsorbent|journal=Journal of Applied Polymer Science|volume=129|issue=6|pages=3439–3446|year=2013|last1=Khazaei|first1=Ardeshir|last2=Kazem-Rostami|first2=Masoud|last3=Zare|first3=Abdolkarim|last4=Moosavi-Zare|first4=Ahmad Reza|last5=Sadeghpour|first5=Mahdieh|last6=Afkhami|first6=Abbas}}

:{{chem2|[C6H5N2]+ + H2O → C6H5OH + N2 + H+}}

This reaction goes by the German name Phenolverkochung ("cooking down to yield phenols"). The phenol formed may react with the diazonium salt and hence the reaction is carried in the presence of an acid which suppresses this further reaction.{{cite journal|author=R. H. F. Manske|doi=10.15227/orgsyn.008.0080|title=m-Nitrophenol|journal=Org. Synth. |volume=8|pages=80|year=1928}} A Sandmeyer-type hydroxylation is also possible using {{chem2|Cu2O}} and {{chem2|Cu(2+)}} in water.

Nitrobenzene can be obtained by treating benzenediazonium fluoroborate with sodium nitrite in presence of copper. Alternatively, the diazotisation of the aniline can be conducted in presence of cuprous oxide, which generates cuprous nitrite in situ:

:{{chem2|[C6H5N2]+ + CuNO2 → C6H5NO2 + N2 + Cu+}}

The cyano group usually cannot be introduced by nucleophilic substitution of haloarenes, but such compounds can be easily prepared from diazonium salts. Illustrative is the preparation of benzonitrile using the reagent cuprous cyanide:

:{{chem2|[C6H5N2]+ + CuCN → C6H5CN + Cu+ + N2}}

This reaction is a special type of Sandmeyer reaction.

Two research groups reported trifluoromethylations of diazonium salts in 2013. Goossen reported the preparation of a {{chem2|CuCF3}} complex from CuSCN, {{chem2|TMSCF3}}, and {{chem2|Cs2CO3}}. In contrast, Fu reported the trifluoromethylation using Umemoto's reagent (S-trifluoromethyldibenzothiophenium tetrafluoroborate) and Cu powder (Gattermann-type conditions). They can be described by the following equation:

:{{chem2|[C6H5N2]+ + [CuCF3] → C6H5CF3 + [Cu]+ + N2}}

The bracket indicates that other ligands on copper are likely present but are omitted.

{{Further|Leuckart thiophenol reaction}}

Diazonium salts can be converted to thiols in a two-step procedure. Treatment of benzenediazonium chloride with potassium ethylxanthate followed by hydrolysis of the intermediate xanthate ester gives thiophenol:

:{{chem2|[C6H5N2]+ + C2H5OCS2- → C6H5SC(S)OC2H5 + N2}}

:{{chem2|C6H5SC(S)OC2H5 + H2O → C6H5SH + HOC(S)OC2H5}}

The aryl group can be coupled to another using arenediazonium salts. For example, treatment of benzenediazonium chloride with benzene (an aromatic compound) in the presence of sodium hydroxide gives diphenyl:

:{{chem2|[C6H5N2]+Cl- + C6H6 → (C6H5)2 + N2 + HCl}}

This reaction is known as the Gomberg–Bachmann reaction. A similar conversion is also achieved by treating benzenediazonium chloride with ethanol and copper powder.

A Bpin (pinacolatoboron) group, of use in Suzuki-Miyaura cross coupling reactions, can be installed by reaction of a diazonium salt with bis(pinacolato)diboron in the presence of benzoyl peroxide (2 mol %) as an initiator:.{{Cite journal|last1=Wu|first1=Jie|last2=Gao|first2=Yueqiu|last3=Qiu|first3=Guanyinsheng|last4=He|first4=Linman|date=2014-08-20|title=Removal of amino groups from anilines through diazonium salt-based reactions|journal=Organic & Biomolecular Chemistry|language=en|volume=12|issue=36|pages=6965–6971|doi=10.1039/C4OB01286K|pmid=25093920|issn=1477-0539}} Alternatively similar borylation can be achieved using transition metal carbonyl complexes including dimanganese decacarbonyl.{{Cite journal|url=https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202004568|doi=10.1002/chem.202004568|title=Light- and Manganese-Initiated Borylation of Aryl Diazonium Salts: Mechanistic Insight on the Ultrafast Time-Scale Revealed by Time-Resolved Spectroscopic Analysis|year=2020|last1=Fairlamb|first1=Ian|last2=Firth|first2=James D.|last3=Hammarback|first3=L. Anders|last4=Burden|first4=Thomas J.|last5=Eastwood|first5=Jonathan B.|last6=Donald|first6=James R.|last7=Horbaczewskyj|first7=Chris S.|last8=McRobie|first8=Matthew T.|last9=Tramaseur|first9=Adam|last10=Clark|first10=Ian P.|last11=Towrie|first11=Michael|last12=Robinson|first12=Alan|last13=Krieger|first13=Jean-Philippe|last14=Lynam|first14=Jason M.|journal=Chemistry – A European Journal|volume=27|issue=12|pages=3979–3985|pmid=33135818|s2cid=226232322}}

:{{chem2|[C6H5N2]+X– + pinB\sBpin → C6H5Bpin + X\sBpin + N2}}

A formyl group, –CHO, can be introduced by treating the aryl diazonium salt with formaldoxime ({{chem2|H2C\dNOH}}), followed by hydrolysis of the aryl aldoxime to give the aryl aldehyde.{{Cite web|title=Organic Syntheses Procedure|url=http://orgsyn.org/demo.aspx?prep=CV5P0139|url-status=live|access-date=2021-05-04|website=2-bromo-4-methylbenzaldehyde|language=en|archive-url=https://web.archive.org/web/20131220161412/http://www.orgsyn.org:80/demo.aspx?prep=cv5p0139 |archive-date=2013-12-20 }} This reaction is known as the Beech reaction.{{Cite journal|last=Beech|first=W. F.|date=1954-01-01|title=Preparation of aromatic aldehydes and ketones from diazonium salts|url=https://pubs.rsc.org/en/content/articlelanding/1954/jr/jr9540001297|journal=Journal of the Chemical Society (Resumed)|language=en|pages=1297–1302|doi=10.1039/JR9540001297|issn=0368-1769}}

• by organic reduction at an electrode
• by mild reducing agents such as ascorbic acid (vitamin C){{cite journal|doi=10.1002/anie.201309761 | pmid=24453180 | volume=53 | issue=8 | title=Ascorbic Acid as an Initiator for the Direct C-H Arylation of (Hetero)arenes with Anilines Nitrosated In Situ | year=2014 | journal=Angewandte Chemie International Edition | pages=2181–2185 | author=Pinacho Crisóstomo Fernando}}
• by gamma radiation from solvated electrons generated in water
• photoinduced 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 solvent serving as electron donor

Benzenediazonium chloride reacts with compounds containing activated double bonds to produce phenylated products. The reaction is called the Meerwein arylation:

:{{chem2|[C6H5N2]+Cl- + ArCH\dCH\sCOOH → ArCH\dCH\sC6H5 + N2 + CO2 + HCl}}

In their reactions with metal complexes, diazonium cations behave similarly to {{chem2|NO+}}. For example, low-valent metal complexes add with diazonium salts. Illustrative complexes are {{chem2|[Fe(CO)2(PPh3)2(N2Ph)]+}} and the chiral-at-metal complex {{chem2|Fe(CO)(NO)(PPh3)(N2Ph)}}.{{cite journal |last1= Sutton |first1= D |year= 1993 |title= Organometallic Diazo Compounds |journal= Chem. Rev. |volume= 93 |issue= 3 |pages= 905–1022 |doi= 10.1021/cr00019a008 }}

In a potential application in nanotechnology, the diazonium salts 4-chlorobenzenediazonium tetrafluoroborate very efficiently functionalizes single wall nanotubes.{{cite journal | doi = 10.1021/ja053998c | volume=127 | title=Green Chemical Functionalization of Single-Walled Carbon Nanotubes in Ionic Liquids | year=2005 | journal=Journal of the American Chemical Society | pages=14867–14870 | last1 = Price | first1 = B. Katherine| issue=42 | pmid=16231941 }} 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 substituents 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).{{Cite journal | title = Direct Covalent Grafting of Conjugated Molecules onto Si, GaAs, and Pd Surfaces from Arenediazonium Salts |author1=Michael P. Stewart |author2=Francisco Maya |author3=Dmitry V. Kosynkin |author4=Shawn M. Dirk |author5=Joshua J. Stapleton |author6=Christine L. McGuiness |author7=David L. Allara |author8=James M. Tour |display-authors=3 |journal= J. Am. Chem. Soc. |doi= 10.1021/ja0383120 |year= 2004 |volume= 126 |pages= 370–8 |pmid= 14709104 |issue= 1}} 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: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.

Image:DiazoniumSaltApplicationSiliconWafer.png

So far grafting of diazonium salts on metals has been accomplished on iron, cobalt, nickel, platinum, palladium, zinc, copper and gold surfaces.{{Cite journal|last1=Bélanger|first1=Daniel|last2=Pinson|first2=Jean|date=2011|title=Electrografting: a powerful method for surface modification|url=http://xlink.rsc.org/?DOI=c0cs00149j|journal=Chemical Society Reviews|language=en|volume=40|issue=7|pages=3995–4048|doi=10.1039/c0cs00149j|pmid=21503288|issn=0306-0012}} Also grafting to diamond surfaces has been reported.{{cite journal | title = Chemical Grafting of Biphenyl Self-Assembled Monolayers on Ultrananocrystalline Diamond |author1=S.Q. Lud |author2=M. Steenackers |author3=P. Bruno |author4=D.M. Gruen |author5=P. Feulner |author6=J.A. Garrido |author7=M. Stutzmann |display-authors=3 |journal= J. Am. Chem. Soc. |doi= 10.1021/ja0657049 |year= 2006 |volume= 128 |pages= 16884–91 |pmid= 17177439 |issue= 51}} One interesting question raised is the actual positioning on the aryl group on the surface. An in silico study {{cite journal |title= Structure and Bonding between an Aryl Group and Metal Surfaces |author1=De-en Jiang |author2=Bobby G. Sumpter |author3=Sheng Dai |journal= J. Am. Chem. Soc. |doi= 10.1021/ja061439f |year= 2006 |volume= 128 |pages= 6030–1 |pmid= 16669660 |issue= 18|s2cid=41590197 }} 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.

Diazonium salts can be reduced with stannous chloride ({{chem2|SnCl2}}) to the corresponding hydrazine derivatives. This reaction is particularly useful in the Fischer indole synthesis of triptan compounds and indometacin. The use of sodium dithionite is an improvement over stannous chloride since it is a cheaper reducing agent with fewer environmental problems.

Alkanediazonium ions, otherwise rarely encountered in organic chemistry, are implicated as the causative agents in the carcinogens. Specifically, nitrosamines are thought to undergo metabolic activation to produce alkanediazonium species.

File:Ndma activ.svg

Solid diazonium halides are often dangerously explosive, and fatalities and injuries have been reported.

The nature of the anions affects stability of the salt. Arenediazonium perchlorates, such as nitrobenzenediazonium perchlorate, have been used to initiate explosives.

• Diazo
• Diazo printing process
• Benzenediazonium chloride
• Triazene cleavage
• Dinitrogen complex

{{Reflist}}

• {{cite web |publisher= Michigan State University |author= W. Reusch |work= VirtualText of Organic Chemistry |title= Reactions of Amines |url= http://www.cem.msu.edu/~reusch/VirtualText/amine2.htm |url-status= dead |archive-url= https://archive.today/20121212131033/http://www.cem.msu.edu/~reusch/VirtualText/amine2.htm |archive-date= 2012-12-12 }}

{{Organic reactions}}

Category:Organic compounds

Category:Carbon-heteroatom bond forming reactions

Category:Functional groups

Category:Organonitrogen compounds