{{Short description|Powerful oxidizing agent}} {{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 464199379 | Name = Peroxymonosulfuric acid | ImageFile = Peroxomonoschwefelsäure.svg | ImageClass = skin-invert-image | ImageFile_Ref = {{chemboximage|correct|??}} | ImageName = Skeletal formula of peroxymonosulfuric acid | ImageFile1 = Caro's-acid-3D-balls.png | ImageClass1 = bg-transparent | ImageFile1_Ref = {{chemboximage|correct|??}} | ImageName1 = Ball and stick model of peroxymonosulfuric acid | IUPACNames = Peroxysulfuric acid<br />Sulfuroperoxoic acid<ref name="redbookname">{{RedBookRef|page=139}}</ref> | SystematicName = (Dioxidanido)hydroxidodioxidosulfur<ref name="redbookname"/><ref>{{Cite web|title = Peroxysulfuric acid (CHEBI:29286)|url = http://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:29286|work = Chemical Entities of Biological Interest|publisher = European Bioinformatics Institute|access-date = 17 November 2011|location = UK|date = 20 November 2007}}</ref> | OtherNames = Peroxosulfuric acid<ref name="redbookname"/><br />Peroxomonosulfuric acid{{Citation needed|date = November 2011}}<br /> Persulfuric acid{{Citation needed|date = November 2011}}<br />Caro's acid |Section1={{Chembox Identifiers | CASNo = 7722-86-3 | CASNo_Ref = {{cascite|changed|CAS}} | UNII_Ref = {{fdacite|correct|FDA}} | UNII = JC6U8R2UJ9 | PubChem = 2754594 | ChemSpiderID = 2035480 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | EINECS = 231-766-6 | UNNumber = 1483 | ChEBI = 29286 | ChEBI_Ref = {{ebicite|correct|EBI}} | Gmelin = 101039 | SMILES = OOS(O)(=O)=O | SMILES1 = [O].[O].OOSO | StdInChI = 1S/H2O5S/c1-5-6(2,3)4/h1H,(H,2,3,4) | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = FHHJDRFHHWUPDG-UHFFFAOYSA-N | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} }} |Section2={{Chembox Properties | Formula = {{Chem|H|2|SO|5}} | MolarMass = 114.078 g mol<sup>−1</sup> | Appearance = White crystals{{cn|date=November 2025}}{{dubious|date=November 2025}} | Density = 2.239 g cm<sup>−3</sup> | ConjugateBase = Peroxomonosulfate | pKa = 1, 9.3<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&nbsp;176}}</ref> | MeltingPt = 45 °C }} |Section3={{Chembox Structure | Coordination = Tetrahedral at S }} |Section4={{Chembox Hazards | MainHazards = strong oxidizer }} }} '''Peroxymonosulfuric acid''', also known as '''persulfuric acid''', '''peroxysulfuric acid''' is the inorganic compound with the formula {{chem2|H2SO5}}. It is a white solid. It is a component of '''Caro's acid''', which is a solution of peroxymonosulfuric acid in sulfuric acid containing small amounts of water.<ref name=Ullmann/> Peroxymonosulfuric acid is a very strong oxidant (''E''<sup>0</sup>&nbsp;= +2.51&nbsp;V).

==Structure== In peroxymonosulfuric acid, the S(VI) center adopts its characteristic tetrahedral geometry; the connectivity is indicated by the formula HO–O–S(O)<sub>2</sub>–OH. The S-O-''H'' proton is more acidic.<ref name=Ullmann>{{cite book |last1=Jakob |first1=Harald |last2=Leininger |first2=Stefan |last3=Lehmann |first3=Thomas |last4=Jacobi |first4=Sylvia |last5=Gutewort |first5=Sven |date=2007 |chapter=Peroxo Compounds, Inorganic |title=Ullmann's Encyclopedia of Industrial Chemistry | location = Weinheim, Germany | publisher = Wiley-VCH| doi=10.1002/14356007.a19_177.pub2 | url = https://onlinelibrary.wiley.com/doi/10.1002/14356007.a19_177.pub2 | access-date = 4 November 2025 | url-access = subscription | isbn=9783527306732}}</ref>

==History== The German chemist Heinrich Caro first reported investigations of mixtures of hydrogen peroxide and sulfuric acid.<ref>{{cite journal |first=H. |last=Caro |year=1898 |title=Zur Kenntniss der Oxydation aromatischer Amine |trans-title=[Contribution] to [our] knowledge of the oxidation of aromatic amines |journal=Zeitschrift für angewandte Chemie |volume=11 |issue=36 |pages=845–846 |url=http://babel.hathitrust.org/cgi/pt?id=mdp.39015073166319;view=1up;seq=855 |doi=10.1002/ange.18980113602 |url-access=subscription }}</ref>

==Synthesis and production== {{refimprove section|date=November 2025}} One laboratory scale preparation of Caro's acid involves the combination of chlorosulfuric acid and hydrogen peroxide:<ref name=Brauer>{{Cite book | author = Brauer, G. | date= 1965 |title= Handbook of Preparative Inorganic Chemistry | volume = 1 | pages = 388–389 | url= |access-date= | location = New York, NY | publisher = Academic Press | language=en-US }}</ref>

:{{chem2 | H2O2 + ClSO2OH <-> H2SO5 + HCl }}

Patents include more than one reaction for preparation of Caro's acid, usually as an intermediate for the production of potassium monopersulfate (PMPS), a bleaching and oxidizing agent. One route employs the following reaction:<ref name="Martin patent">{{Citation |title=A method and apparatus for producing a peroxyacid solution |url=https://patents.google.com/patent/WO2005016511A1/da |access-date=2018-10-12}}{{primary source inline|date=November 2025}}</ref>{{better source|date=November 2025}}

:{{chem2 | H2O2 + H2SO4 <-> H2SO5 + H2O }} This reaction occurs in the piranha solution.<ref>{{Cite journal |last=O'Brein |first=Sean C. |date=1996 |title=The chemistry of the semiconductor industry |url=https://xlink.rsc.org/?DOI=cs9962500393 |journal=Chemical Society Reviews |language=en |volume=25 |issue=6 |pages=393 |doi=10.1039/cs9962500393 |issn=0306-0012|url-access=subscription }}</ref>

==Uses in industry== {{refimprove section|date=April 2026}}

{{Chem|H|2|S|O|5}} and Caro's acid have been used for a variety of disinfectant and cleaning applications, e.g., swimming pool treatment and denture cleaning. It is used in gold mining to destroy the cyanide in the waste stream (tailings).<ref>{{Cite journal |last=Schmidt |first=Hugo Gerald |date=2022-01-24 |title=Safe Piranhas: A Review of Methods and Protocols |url=https://doi.org/10.1021/acs.chas.1c00094 |journal=ACS Chemical Health & Safety |volume=29 |issue=1 |pages=54–61 |doi=10.1021/acs.chas.1c00094|url-access=subscription }}</ref>

Alkali metal salts of {{Chem|H|2|S|O|5}}, especially oxone, are widely investigated.<ref>{{cite journal | last1=Lim | first1=Hyun Jeong | last2=Kim | first2=David J. | last3=Rigby | first3=Kali | display-authors=etal | title=Peroxymonosulfate-Based Electrochemical Advanced Oxidation: Complication by Oxygen Reduction Reaction | journal=Environmental Science & Technology | url=https://pubs.acs.org/doi/10.1021/acs.est.3c06156 | doi=10.1021/acs.est.3c06156 | access-date=21 December 2025}}</ref>

==Hazards== These peroxy acids can be explosive. Explosions have been reported at Brown University<ref>{{cite journal | last1 = Edwards | first1 = J.O. | journal = Chem. Eng. News | volume = 33 | pages = 3336 | year = 1955 | doi = 10.1021/cen-v033n032.p3336 | title = Safety | issue = 32}}</ref> and Sun Oil. As with all strong oxidizing agents, peroxysulfuric acid is incompatible with organic compounds.

==See also== * Peroxydisulfuric acid {{Chem|H|2|S|2|O|8}} * Peroxomonosulfate

==References== {{reflist}}

{{Hydrogen compounds}} {{Persulfates}}

Category:Hydrogen compounds Category:Sulfur oxoacids Category:Liquid explosives Category:Persulfates Category:Peroxy acids Category:Explosive chemicals