{{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 477003468 | ImageFile1 = Hypoiodige-Säure.png | ImageFileL1 = Hypoiodous-acid-3D-vdW.png | ImageCaptionL1 = {{legend|white|Hydrogen, H}}{{legend|red|Oxygen, O}}{{legend|rgb(128, 0, 104)|Iodine, I}} | ImageFileR1 = Hypoiodous-acid-3D-balls.png | IUPACName = Hypoiodous acid | OtherNames = |Section1={{Chembox Identifiers | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 109942 | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/HIO/c1-2/h2H | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = GEOVEUCEIQCBKH-UHFFFAOYSA-N | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 14332-21-9 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = 2PYC923C5W | PubChem = 123340 | RTECS = | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = 29231 | SMILES = IO}} |Section2={{Chembox Properties | Formula = HOI | H=1|I=1|O=1 | Appearance = | Density = | Solubility = | MeltingPt = | BoilingPt = | BoilingPt_notes = | pKa = 10.5 (in water, estimate)<ref name=P82db>{{cite book|title=Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution|editor-first=D.&nbsp;D.|editor-last=Perrin|edition=2nd|series=IUPAC Chemical Data|issue=29|publisher=Pergamon|location=Oxford|year=1982|publication-date=1984|orig-date=1969|lccn=82-16524|isbn=0-08-029214-3|at=Entry 119}}</ref> | Viscosity = | ConjugateBase = Hypoiodite }} |Section7={{Chembox Hazards | FlashPt = | NFPA-H = | NFPA-F = | NFPA-R = | NFPA-S = }} |Section9={{Chembox Related | OtherCompounds = {{ubl|Hypofluorous acid|Hypochlorous acid|Hypobromous acid}} }} }}

'''Hypoiodous acid''' is an inorganic compound with the chemical formula {{chem2|HIO|auto=1}}. It forms when an aqueous solution of iodine is treated with mercuric or silver salts. It rapidly decomposes by disproportionation:<ref name = "Wiberg&Holleman">{{cite book|last1=Holleman|first1=A.F.|title=Inorganic chemistry|date=2001|publisher=Academic Press, W. de Gruyter.|location=San Diego, Calif. : Berlin|isbn=0-12-352651-5|edition=1st English|editor-first=Nils|editor-last=Wiberg}}</ref> :{{chem2|5 HIO → HIO3 + 2 I2 + 2 H2O}} Hypoiodous acid is a weak acid with a p''K''<sub>a</sub> of about 11. The conjugate base is '''hypoiodite''' ({{chem2|IO−}}). Salts of this anion can be prepared by treating iodine with alkali hydroxides. They rapidly disproportionate to form iodides and iodates,<ref name = "Wiberg&Holleman"/> but an iodine–hydroxide mixture can be used an in situ preparation of hypoiodite for other reactions.<ref name=haloform>{{cite journal |doi=10.1021/ja01308a043 |title=The Haloform Reaction. XVI. The Action of Hypoiodite on Hindered Ketones<sup>1</sup> |date=1935 |last1=Johnson |first1=Robert |last2=Fuson |first2=Reynold C. |journal=Journal of the American Chemical Society |volume=57 |issue=5 |pages=919–920 |bibcode=1935JAChS..57..919J }}</ref>

Ammonium hypoiodites can be formed by oxidation of the analogous iodide salts. These and also sodium hypoiodite are useful as oxidizing agents for a various types of organic compounds and also for a reaction analogous to the haloform reaction.<ref name=haloform/>

Hypoiodite is one of the active oxidizing agents generated by lactoperoxidase as part of the mammalian innate immune system.<ref>{{cite journal |doi= 10.1002/pro.4230 |title= Structural evidence of the oxidation of iodide ion into hyper-reactive hypoiodite ion by mammalian heme lactoperoxidase |date= 2022 |last1= Singh |first1= Prashant K. |last2= Ahmad |first2= Nayeem |last3= Yamini |first3= Shavait |last4= Singh |first4= Rashmi P. |last5= Singh |first5= Amit K. |last6= Sharma |first6= Pradeep |last7= Smith |first7= Michael L. |last8= Sharma |first8= Sujata |last9= Singh |first9= Tej P. |journal= Protein Science |volume= 31 |issue= 2 |pages= 384–395 |pmid= 34761444 |pmc= 8819834 }}</ref><ref>{{cite journal | doi = 10.1021/bi026326x | title = Reaction of Lactoperoxidase Compound I with Halides and Thiocyanate | date = 2002 | last1 = Furtmüller | first1 = Paul Georg | last2 = Jantschko | first2 = Walter | last3 = Regelsberger | first3 = Günther | last4 = Jakopitsch | first4 = Christa | last5 = Arnhold | first5 = Jürgen | last6 = Obinger | first6 = Christian | journal = Biochemistry | volume = 41 | issue = 39 | pages = 11895–11900 | pmid = 12269834 }}</ref>

==Other oxyacids== Hypoiodous acid is part of a series of oxyacids in which iodine can assume oxidation states of −1, +1, +3, +5, or +7. A number of neutral iodine oxides are also known.

{| class="wikitable" |- ! Iodine oxidation state | −1 | +1 | +3 | +5 | +7 |- ! Name | Hydrogen iodide | '''Hypoiodous acid''' | Iodous acid | Iodic acid | Periodic acid |- ! Formula | HI | HIO | HIO<sub>2</sub> | HIO<sub>3</sub> | HIO<sub>4</sub> or H<sub>5</sub>IO<sub>6</sub> |}

==References== {{reflist}} {{Hydrogen compounds}} {{iodine compounds}}

Category:Hypoiodites Category:Oxidizing acids Category:Triatomic molecules Category:Halogen oxoacids

{{Inorganic-compound-stub}}