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<title>Azoxy compounds</title>

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Azoxy compounds

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In <a href="Chemistry" title="Chemistry">chemistry</a>, azoxy compounds are a group of <a href="Organic_compound" title="Organic compound">organic compounds</a> sharing a common <a href="Functional_group" title="Functional group">functional group</a> with the general structure <style data-mw-deduplicate="TemplateStyles:r1123817410">

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</style>R−N=N+(−O−)−R.<a href="#cite_note-1">[1]</a> They are considered <a href="Amine_oxide" title="Amine oxide">N-oxides</a> of <a href="Azo_compound" title="Azo compound">azo compounds</a>. Azoxy compounds are <a href="1%2C3-dipole" title="1,3-dipole">1,3-dipoles</a> and <a href="1%2C3-dipolar_cycloaddition" class="mw-redirect" title="1,3-dipolar cycloaddition">cycloadd to double bonds</a>. Most azoxy-containing compounds have <a href="Aryl" class="mw-redirect" title="Aryl">aryl</a> substituents.

<div class="mw-heading mw-heading2"><h2 id="Preparation">Preparation</h2></div>

Azoxybenzene and its derivatives are typically prepared by <a href="Redox" title="Redox">reduction</a> of <a href="Nitro_compound" title="Nitro compound">nitro compounds</a>, such as the reduction of <a href="Nitrobenzene" title="Nitrobenzene">nitrobenzene</a> with arsenous oxide.<a href="#cite_note-2">[2]</a> Such reactions are proposed to proceed via the intermediacy of the <a href="Nitroso" title="Nitroso">nitroso</a> compounds and <a href="Hydroxylamines" class="mw-redirect" title="Hydroxylamines">hydroxylamines</a>, e.g. <a href="Phenylhydroxylamine" class="mw-redirect" title="Phenylhydroxylamine">phenylhydroxylamine</a> and <a href="Nitrosobenzene" title="Nitrosobenzene">nitrosobenzene</a> (Ph = <a href="Phenyl" class="mw-redirect" title="Phenyl">phenyl</a>, C6H5):<a href="#cite_note-Patai1-3">[3]</a>: 445 <math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {PhNHOH + PhNO -> PhN(O)NPh + H2O}}}">

<mtext>PhNHOH</mtext>

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<annotation encoding="application/x-tex">{\displaystyle {\ce {PhNHOH + PhNO -> PhN(O)NPh + H2O}}}</annotation>

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Nitrosocarbamate <a href="Ester" title="Ester">esters</a> decarboxylate in strong base to an azotate susceptible to strong alkylation agents:

An alternative route involves oxidation of <a href="Azobenzene" title="Azobenzene">azobenzenes</a> with <a href="Peroxy_acid" title="Peroxy acid">peroxy acids</a>.<a href="#cite_note-Patai1-3">[3]</a>: 96–100

<div class="mw-heading mw-heading2"><h2 id="Structure">Structure</h2></div>

Azoxybenzene compounds are more stable as their <a href="Trans_isomer" class="mw-redirect" title="Trans isomer">trans isomer</a> isomer. In Ph2N2O, the N-N and N-O bond lengths are is 1.24 and 1.255 Å respectively, corresponding to some <a href="Double_bond" title="Double bond">double bonds character</a>. The CNNC and CNNO are near 176°.<a href="#cite_note-XRD-4">[4]</a>

trans-Azoxydibenzene's <a href="Resonance_form" class="mw-redirect" title="Resonance form">resonance form</a> with a negative <a href="Formal_charge" title="Formal charge">formal charge</a> on oxygen (–N=N+(O−)–) corresponds to a theoretical 6‑<a href="Debye" title="Debye">D</a> <a href="Dipole_moments_of_molecules" class="mw-redirect" title="Dipole moments of molecules">dipole moment</a>. However, the observed moment is only 4.7 D, suggesting a substantial resonance contribution in which the other nitrogen bears negative charge (–N−–N+(=O)–).<a href="#cite_note-Patai2-5">[5]</a>: 42

<div class="mw-heading mw-heading2"><h2 id="Reactions">Reactions</h2></div>

Under <a href="Ultraviolet_light" class="mw-redirect" title="Ultraviolet light">ultraviolet light</a> transazobenzene compounds isomerize to their cis isomers, analogous to azobenzene. Similar reaction conditions can instead cause isomery to an ortho-azophenol, or migration of the oxygen atom across the two nitrogens.<a href="#cite_note-Patai1-3">[3]</a>: 101, 766, 1008

Unlike <a href="Azo_compound" title="Azo compound">azo compounds</a>, azoxy compounds do not fragment thermally to lose <a href="Nitrous_oxide" title="Nitrous oxide">nitrous oxide</a>; the process is believed <a href="Selection_rule" title="Selection rule">forbidden by orbital symmetries</a>. Correspondingly, the reaction is possible under UV light with wavelength approximately 220 nm.<a href="#cite_note-Patai1-3">[3]</a>: 922, 1007

The azoxy group is <a href="Electron-withdrawing" class="mw-redirect" title="Electron-withdrawing">electron-withdrawing</a>, but in non-oxidizing media, aliphatic <a href="Locant" title="Locant">α</a> hydrogens must be situated between two azoxy groups to appreciably dissociate. <a href="Organolithium_reagent" title="Organolithium reagent">Alkyllithia</a> replace the hydrogens, but with reduction:

Basic <a href="Oxidant" class="mw-redirect" title="Oxidant">oxidants</a> abstract α hydrogens in a <a href="Radical_reaction" class="mw-redirect" title="Radical reaction">free-radical process</a>, leading to dimerization.<a href="#cite_note-Patai1-3">[3]</a>: 712–716

Azoxyarenes ortho to a benzylic carbon with good <a href="Leaving_group" title="Leaving group">leaving group</a> eliminate the leaving group to give an indazolone (the <a href="Davis-Beirut_reaction" class="mw-redirect" title="Davis-Beirut reaction">Davis-Beirut reaction</a>).<a href="#cite_note-Patai1-3">[3]</a>: 835–836

Azoxy compounds are weak bases, and unstable to strong acids. Azoxyarenes undergo the <a href="Wallach_rearrangement" title="Wallach rearrangement">Wallach rearrangement</a> to para-azophenols; primary and secondary azoxyaliphates <a href="Tautomerize" class="mw-redirect" title="Tautomerize">tautomerize</a> to a <a href="Hydrazide" title="Hydrazide">hydrazamide</a>.<a href="#cite_note-Patai1-3">[3]</a>: 173–174, 621, 837

The two aryl groups in azoxyarenes undergo <a href="Electrophilic_aromatic_substitution" title="Electrophilic aromatic substitution">electrophilic aromatic substitution</a> differently. In the case of azoxybenzene, PhNN(O)– reacts at the meta position, while PhN(O)N– reacts at the ortho and para positions.<a href="#cite_note-Patai1-3">[3]</a>: 247,712–713

Electrochemical reduction converts azoxyarenes to <a href="Azo_compounds" class="mw-redirect" title="Azo compounds">azo compounds</a>. Single-electron reductants give a deep-blue radical anion, which dimerizes in <a href="Aqueous_solution" title="Aqueous solution">aqueous solution</a> to the corresponding azo compound and <a href="Hydrogen_peroxide" title="Hydrogen peroxide">hydrogen peroxide</a>. Strong reducing agents such as <a href="Lithium_aluminum_hydride" class="mw-redirect" title="Lithium aluminum hydride">lithium aluminum hydride</a> also <a href="Hydrogenolysis" title="Hydrogenolysis">hydrogenolyze</a> electronegative ortho or para arene substituents, but <a href="Catalytic_hydrogenation" class="mw-redirect" title="Catalytic hydrogenation">catalytic hydrogenation</a> selects out the azoxy link. Conversely, <a href="Sodium_borohydride" title="Sodium borohydride">sodium borohydride</a> preserves the azoxy group even as it reduces arene substituents.<a href="#cite_note-Patai1-3">[3]</a>: 452–455, 616–617, 619–620, 924–925

<div class="mw-heading mw-heading2"><h2 id="Safety">Safety</h2></div>

Alkyl azoxy compounds, e.g. <a href="Azoxymethane" title="Azoxymethane">azoxymethane</a> are suspected to be genotoxic.<a href="#cite_note-6">[6]</a>

<ul><li><a href="Azobenzene_dioxide" title="Azobenzene dioxide">azobenzene dioxide</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

<li id="cite_note-1"><a href="#cite_ref-1">^</a> <a href="International_Union_of_Pure_and_Applied_Chemistry" title="International Union of Pure and Applied Chemistry">IUPAC</a>, <a href="IUPAC_books" class="mw-redirect" title="IUPAC books">Compendium of Chemical Terminology</a>, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "<a rel="nofollow" class="external text" href="https://goldbook.iupac.org/terms/view/A00567.html">azoxy compounds</a>". <style data-mw-deduplicate="TemplateStyles:r1238218222">

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</style><a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1351%2Fgoldbook.A00567">10.1351/goldbook.A00567</a>

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<li id="cite_note-2"><a href="#cite_ref-2">^</a> H. E. Bigelow and Albert Palmer "Azoybenzene" Org. Synth. 1931, 11, 16. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.15227%2Forgsyn.011.0016">10.15227/orgsyn.011.0016</a>

</li>

<li id="cite_note-Patai1-3">^ <a href="#cite_ref-Patai1_3-0">a</a> <a href="#cite_ref-Patai1_3-1">b</a> <a href="#cite_ref-Patai1_3-2">c</a> <a href="#cite_ref-Patai1_3-3">d</a> <a href="#cite_ref-Patai1_3-4">e</a> <a href="#cite_ref-Patai1_3-5">f</a> <a href="#cite_ref-Patai1_3-6">g</a> <a href="#cite_ref-Patai1_3-7">h</a> <a href="#cite_ref-Patai1_3-8">i</a> <cite id="CITEREFPatai1975" class="citation book cs1">Patai, Saul, ed. (1975-01-01). The Chemistry of the Hydrazo, Azo and Azoxy Groups. The Chemistry of Functional Groups. Vol. 1. Chichester, UK: John Wiley & Sons, Ltd. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1002%2F0470023414">10.1002/0470023414</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-471-66924-1</bdi>.</cite>

</li>

<li id="cite_note-XRD-4">^ <a href="#cite_ref-XRD_4-0">a</a> <a href="#cite_ref-XRD_4-1">b</a> <cite id="CITEREFGonzález_MartínezBernès2007" class="citation journal cs1">González Martínez, Sandra Patricia; Bernès, Sylvain (2007). "trans -Diphenyldiazene Oxide". Acta Crystallographica Section E: Structure Reports Online. 63 (8): o3639. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2007AcCrE..63O3639G">2007AcCrE..63O3639G</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1107%2FS1600536807035787">10.1107/S1600536807035787</a>.</cite>

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<li id="cite_note-Patai2-5"><a href="#cite_ref-Patai2_5-0">^</a> <cite id="CITEREFPatai1977" class="citation book cs1">Patai, Saul, ed. (1977-03-16). <a rel="nofollow" class="external text" href="http://doi.wiley.com/10.1002/9780470771501">Double-Bonded Functional Groups</a>. The Chemistry of Functional Groups. Vol. 1. Chichester, UK: John Wiley & Sons, Ltd. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1002%2F9780470771501">10.1002/9780470771501</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-470-77150-1</bdi>.</cite>

</li>

<li id="cite_note-6"><a href="#cite_ref-6">^</a> Guideline On The Limits Of Genotoxic Impurities <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20060904034322/http://www.emea.eu.int/pdfs/human/swp/519902en.pdf">"Archived copy"</a> (PDF). Archived from <a rel="nofollow" class="external text" href="http://www.emea.eu.int/pdfs/human/swp/519902en.pdf">the original</a> (PDF) on 2006-09-04. Retrieved 2007-07-11.</cite><code class="cs1-code">{{cite web}}</code>: CS1 maint: archived copy as title (link)

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