| Description | Benzene sulfonic acid is an organo sulfur compound with the formula C6H5SO3H. It is the simplest aromatic sulfonic acid. It forms colorless deliquescent sheet crystals or a white waxy solid that is soluble in water and ethanol, slightly soluble in benzene and insoluble in carbon disulfide and diethyl ether. It is often stored in the form of alkali metal salts. Its aqueous solution is strongly acidic. |
| Chemical Properties | green solid |
| Uses | Benzenesulfonic acid is mainly consumed by conversion to other specialty chemicals. A variety of pharmaceutical drugs are prepared as salts of benzenesulfonic acid and are known as besylates or besilates. The alkali metal salt of benzenesulfonic acid was once widely used in the production of phenol. It acts as an acid catalyst for direct esterification of amino acids and peptides. |
| Uses | Benzenesulfonic acid is an aryl sulfonic acid that can be used to form an organic salt with 5,7-dimethyl-1,8-naphthyridine-2-amine, that can be a synthon for developing supramolecular structures. It can also act as a dopant for the polymerization of pyrrole to form poly(pyrrole), a conducting polymer useful in the development of flexible capacitors. |
| Application | The alkali metal salt of benzene sulfonic acid was once widely used in the production of phenol :
C6H5SO3Na + 2 NaOH → C6H5ONa + Na2SO3
C6H5ONa + HCl → C6H5OH + NaCl
The process has been largely displaced by the Hock process, which generates less waste. Benzene sulfonic acid is mainly consumed by conversion to other specialty chemicals. A variety of pharmaceutical drugs are prepared as salts of benzene sulfonic acid and are known as besylates or besilates. |
| Preparation | Benzene sulfonic acid is prepared from the sulfonation of benzene using concentrated sulfuric acid :
This conversion illustrates aromatic sulfonation, which has been called "one of the most important reactions in industrial organic chemistry.". |
| Definition | ChEBI: The simplest member of the class of a benzenesulfonic acids that consists of a benzene carrying a single sulfo group. |
| Definition | A white crystalline
acid made by sulfonation of benzene. Any
further substitution onto the benzene ring
is directed into the 3 position. |
| Definition | benzenesulphonic acid: A colourlessdeliquescent solid, C6H5SO2OH,m.p. 43–44°C, usually found as anoily liquid. It is made by treating benzenewith concentrated sulphuricacid. Its alkyl derivatives are used asdetergents. |
| Reactions | Benzene sulfonic acid exhibits the reactions typical of other aromatic sulfonic acids, forming sulfonamides , sulfonyl chloride, and esters. The sulfonation is reversed above 220 °C. Dehydration with phosphorus pentoxide gives benzene sulfonic acid anhydride ((C6H5SO2)2O). Conversion to the corresponding benzene sulfonyl chloride (C6H5SO2Cl) is effected with phosphorus penta chloride. It is a strong acid, being dissociated in water. |
| Synthesis Reference(s) | The Journal of Organic Chemistry, 61, p. 1530, 1996 DOI: 10.1021/jo9520710
Tetrahedron Letters, 19, p. 1211, 1978 DOI: 10.1016/S0040-4039(01)94501-0 |
| General Description | Deliquescent needles or large plates. |
| Air & Water Reactions | Slightly soluble in water. |
| Reactivity Profile | Benzenesulfonic acid reacts with bases and many organic compounds. |
| Fire Hazard | Flash point data for Benzenesulfonic acid are not available, however Benzenesulfonic acid is probably combustible. |
| Flammability and Explosibility | Nonflammable |
| Safety Profile | Poison by ingestion,
sbn contact, and probably inhalation. A
severe skin and eye irritant. See also
SULFATES and SULFONATES. |
| Purification Methods | Purify benzenesulfonic acid by dissolving it in a small volume of distilled H2O and stirring with slightly less than the theoretical amount of BaCO3. When effervescence is complete and the solution is still acidic, filter off the insoluble barium benzenesulfonate. The salt is collected and dried to constant weight in vacuo, then suspended in H2O and stirred with a little less than the equivalent (half mol.) of sulfuric acid. The insoluble BaSO4 (containing a little barium benzenesulfonate) is filtered off and the filtrate containing the free acid is evaporated in a high vacuum. The oily residue will eventually crystallise when completely anhydrous. A 32% commercial acid is allowed to fractionally crystallise at room temperature over P2O5 in a vacuum desiccator giving finally colourless deliquescent plates m 52.5o. The anhydrous crystalline acid is deliquescent and should be stored over anhydrous Na2SO4 in the dark and should be used in subdued sunlight as it darkens under sunlight. The main impurity is Fe which readily separates as the Fe salt in the early fractions [Taylor & Vincent J Chem Soc 3218 1952]. The S-benzylisothiuronium salt has m 148o (from EtOH/H2O). It is an IRRITANT to the skin and eyes. [See Adams & Marvel Org Synth Coll Vol I 84 1941, Michael & Adair Chem Ber 10 585 1877, Beilstein 11 IV 27.] |
