Sulfonic acid
organic compound with the structure R−S(=O)₂−OH
In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula R−S(=O)2−OH, where R is an organic alkyl or aryl group and the S(=O)2(OH) group a sulfonyl hydroxide. A sulfonic acid can be thought of as sulfuric acid with one hydroxyl group replaced by an organic substituent. The parent compound (with the organic substituent replaced by hydrogen) is the parent sulfonic acid, HS(=O)2(OH), a tautomer of sulfurous acid, S(=O)(OH)2. Salts or esters of sulfonic acids are called sulfonates.
Preparation
Most sulfonic acids and, indirectly, most sulfonate salts are produced by treatment of organic compounds with sulfur trioxide. One large scale application of this method is the production of alkylbenzenesulfonic acids:
RC6H5 + SO3 → RC6H4SO3H
In this reaction, sulfur trioxide is an electrophile and the arene is the nucleophile. The reaction is an example of electrophilic aromatic substitution.
In a related process, terminal alkenes react with sulfur trioxide to give α-olefin sulfonic acids (and hydroxysulfonic acid):
RCH2CH=CH2 + SO3 → RCH=CHCH2SO3H
Likewise, carboxylic acids react with sulfur trioxide to give the sulfonic acids.
A third large-scale industrial process starts simply with saturated hydrocarbons. Sulfoxidation, similar to the Reed reaction, irradiates a mixture of alkanes, sulfur dioxide and oxygen:
RH + SO2 + 1/2 O2 → RSO3H
UV (or higher-energy) light is usually necessary, but titanium dioxide catalyzes the reaction with visible light.
This brief starts where responsible research should: with the source description of “Sulfonic acid” as organic compound with the structure R−S(=O)₂−OH. Everything that follows is an evidence route, not borrowed authority.
Why this record matters
The subject matters to the general reference register because the source frames it as organic compound with the structure R−S(=O)₂−OH. Its deeper value depends on whether names, dates, institutions and citations support that framing.
Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Jul 29, 2026. The linked authority identifier is Q250437. The Library of Congress control number is sh85130359. 1 of 1 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank.
Overview language is designed for orientation and should not be treated as a substitute for the evidence cited beneath it. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “Sulfonic acid”, its source revision and the description used here.
- Expand the search: follow Sulfonic acid primary sources, Sulfonic acid archive and Sulfonic research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Sulfonic acid”?
- Which cited source is closest to the event, object or claim?
- What terminology or title could unlock a more precise catalogue search?
Search terms from this dossier
This entry incorporates text from “Sulfonic acid” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.