Chlorosulfuric acid

<h2 id="structure-and-properties">Structure and properties</h2>
Chlorosulfuric acid is a <a href="/facts/Tetrahedral_molecular_geometry/583AL1sP">tetrahedral molecule</a>. Its structure was debated for many decades until in 1941 Shrinivasa Dharmatti proved by <a href="/facts/Magnetic_susceptibility/hWMbGTjP">magnetic susceptibility</a> that chlorine is directly bonded to sulfur.<a class="footnote-ref" id="fnref:2" href="#fn:2">2</a><a class="footnote-ref" id="fnref:3" href="#fn:3">3</a>
The formula is more descriptively written SO2(OH)Cl, but HSO3Cl is traditional. It is an intermediate, chemically and conceptually, between <a href="/facts/Sulfuryl_chloride/UtEHXDb8">sulfuryl chloride</a> (SO2Cl2) and <a href="/facts/Sulfuric_acid/Wom6fymJ">sulfuric acid</a> (H2SO4).<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a> The compound is rarely obtained pure. Upon standing with excess sulfur trioxide, it decomposes to pyrosulfuryl chlorides:<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a>

2 ClSO3H + SO3 → H2SO4 + S2O5Cl2
<h2 id="synthesis">Synthesis</h2>
The industrial synthesis entails the reaction of <a href="/facts/Hydrogen_chloride/7Wzkhomd">hydrogen chloride</a> with a <a href="/facts/Oleum/oyT7XMod">solution</a> of <a href="/facts/Sulfur_trioxide/Ijvm08Lq">sulfur trioxide</a> in <a href="/facts/Sulfuric_acid/Wom6fymJ">sulfuric acid</a>:<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a>

HCl + SO3 → ClSO3H
It can also be prepared by the method originally used by acid's discoverer <a href="/facts/Alexander_William_Williamson/TIITFGQP">Alexander William Williamson</a> in 1854,<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a> namely chlorination of sulfuric acid, written here for pedagogical purposes as HSO3(OH) vs. the usual format H2SO4:

<a href="/facts/Phosphorus_pentachloride/oGLG4kDg">PCl5</a> + HSO3(OH) → HSO3Cl + POCl3 + HCl
The latter method is more suited for laboratory-scale operations.
Williamson's discovery disproved then-popular hypothesis that sulfuric acid is a compound of water (which was incorrectly assumed to have formula of HO) and <a href="/facts/Sulfur_trioxide/Ijvm08Lq">sulfur trioxide</a>.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a>

<h2 id="applications">Applications</h2>
ClSO2OH is used to prepare <a href="/facts/Organosulfate/VA9IoLaY">alkyl sulfates</a>, which are useful as <a href="/facts/Detergent/4FLKXR6p">detergents</a> and as chemical intermediates:<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a>

ROH + ClSO3H → ROSO3H + HCl
One historical synthesis of <a href="/facts/Saccharin/PCIjSpIh">saccharin</a> begins with the reaction of <a href="/facts/Toluene/Pzdt8dwD">toluene</a> with ClSO2OH to give the ortho- and <a href="/facts/4-Toluenesulfonyl_chloride/g4jj03Sq">para-toluenesulfonyl chloride</a> derivatives:

CH3C6H5 + 2 ClSO2OH → CH3C6H4SO2Cl + H2SO4 + HCl
Oxidation of the ortho isomer gives the <a href="/facts/Benzoic_acid/7HrmrBYS">benzoic acid</a> derivative that then is cyclized with <a href="/facts/Ammonia/MtLtJFtz">ammonia</a> and neutralized with base to afford saccharin.
Chlorosulfonic acid has been used as an anti-<a href="/facts/Contrail/PmRg5uTn">contrail</a> agent in <a href="/facts/Ryan_Model_147/eNE1rXSg">Ryan Model 147</a> reconnaissance drones,<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> and to produce <a href="/facts/Smoke_screen/s0Wre6Iq">smoke screens</a>.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a><a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>

<h2 id="safety">Safety</h2>
ClSO3H reacts violently with water to yield sulfuric acid and hydrogen chloride, which are corrosive:

ClSO3H + H2O → H2SO4 + HCl
<h2 id="related-halosulfuric-acids">Related halosulfuric acids</h2>
<ul><li><a href="/facts/Fluorosulfonic_acid/HJng4DqN">Fluorosulfonic acid</a>, FSO2OH, is a related <a href="/facts/Strong_acid/vJ4rj6Lu">strong acid</a> with a diminished tendency to evolve <a href="/facts/Hydrogen_fluoride/XfQxlqR6">hydrogen fluoride</a>.</li>
<li>Bromosulfonic acid, BrSO2OH, is unstable, decomposing at its melting point of 8 °C to give <a href="/facts/Bromine/oLfj3C7D">bromine</a>, <a href="/facts/Sulfur_dioxide/jDK1fIDs">sulfur dioxide</a>, and <a href="/facts/Sulfuric_acid/Wom6fymJ">sulfuric acid</a>.</li>
<li>Iodosulfonic acid is not known to occur.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Cremlyn, R. J. (2002). Chlorosulfonic Acid. Royal Society of Chemistry. ISBN 978-0-85404-498-6. <a href="978-0-85404-498-6" target="_blank">978-0-85404-498-6</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Kirk, Raymond Eller; Othmer, Donald Frederick (1964). Encyclopedia of Chemical Technology. Interscience Publishers. <a href="https://books.google.com/books?id=f8tTAAAAMAAJ&q=Dharmatti" target="_blank">https://books.google.com/books?id=f8tTAAAAMAAJ&q=Dharmatti</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Dharmatti, S. S. (1941-05-01). "Magnetism and Molecular Structure of Sulphur Compounds". Proceedings of the Indian Academy of Sciences - Section A. 13 (5): 359–370. doi:10.1007/BF03049293. ISSN 0370-0089. <a href="https://www.ias.ac.in/describe/article/seca/013/05/0359-0370" target="_blank">https://www.ias.ac.in/describe/article/seca/013/05/0359-0370</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. pp. 549–550. <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">Bergen, Elvira; Maas, J.; Baunack, F. (2024). "Chlorosulfuric Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. pp. 1–7. doi:10.1002/14356007.a07_017.pub2. ISBN 978-3527306732. <a href="978-3527306732" target="_blank">978-3527306732</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Bergen, Elvira; Maas, J.; Baunack, F. (2024). "Chlorosulfuric Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. pp. 1–7. doi:10.1002/14356007.a07_017.pub2. ISBN 978-3527306732. <a href="978-3527306732" target="_blank">978-3527306732</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Kirk, Raymond Eller; Othmer, Donald Frederick (1964). Encyclopedia of Chemical Technology. Interscience Publishers. <a href="https://books.google.com/books?id=f8tTAAAAMAAJ&q=Dharmatti" target="_blank">https://books.google.com/books?id=f8tTAAAAMAAJ&q=Dharmatti</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">"The Quiet Revolution". <a href="https://publishing.cdlib.org/ucpressebooks/view?docId=ft5g500723&chunk.id=d0e3659&toc.depth=100&toc.id=d0e3589&brand=ucpress" target="_blank">https://publishing.cdlib.org/ucpressebooks/view?docId=ft5g500723&chunk.id=d0e3659&toc.depth=100&toc.id=d0e3589&brand=ucpress</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Bergen, Elvira; Maas, J.; Baunack, F. (2024). "Chlorosulfuric Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. pp. 1–7. doi:10.1002/14356007.a07_017.pub2. ISBN 978-3527306732. <a href="978-3527306732" target="_blank">978-3527306732</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Method and apparatus for suppressing contrails (PDF). United States Patent and Trademark Office. 1970. <a href="https://patentimages.storage.googleapis.com/6c/7c/d2/62398f0fc22989/US3517505.pdf" target="_blank">https://patentimages.storage.googleapis.com/6c/7c/d2/62398f0fc22989/US3517505.pdf</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">The Royal Navy at War (DVD). London: Imperial War Museum. 2005. <a href="/wiki/Imperial_War_Museum" target="_blank">/wiki/Imperial_War_Museum</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Amos, Jonathan (2018-04-11). "Nazi legacy found in Norwegian trees". BBC News Online. Retrieved 2018-04-17. <a href="https://www.bbc.com/news/science-environment-43727547" target="_blank">https://www.bbc.com/news/science-environment-43727547</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
</ol>

Chlorosulfuric acid open-in-new

Chlorosulfuric acid