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.
Benzenesulfonic acid was first obtained, together with diphenyl sulfone, by E. M ITSCHERLICH in 1834 by heating benzene with fuming sulfuric acid. The industrially important reaction of benzenesulfonic acid with alkali hydroxide to form phenol (alkali fusion) was developed by A. WURTZ and A. KEKULé in 1867 and by P. O. D EGENER in 1878. Until the early 1960s benzenesulfonic acid was used chiefly in the manufacture of phenol. Other phenol syntheses are preferred now.
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.
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.
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.
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.".
Benzenesulfonic acids are used chiefly as intermediates. They are employed in the manufacture of sulfonic acid amides, hydrazides, and esters; of sulfinic acids, sulfones, phenols, and thiophenols; and of other compounds. Sulfonic acids that are substituted with OH and/or NH 2 groups serve as intermediates in the manufacture of finishing agents, optical brighteners, pickling agents, dyes, tanning agents, water-soluble resins, insecticides, ion-exchange resins, wetting agents, pharmaceuticals, polymeric thickeners, plasticizers, etc. Benzenesulfonic acids are also used as such as acidic catalysts and standardizing agents in dye manufacture.
Benzenesulfonic acid is the simplest member of the class of benzenesulfonic acid, which consists of benzene carrying a single sulfur group. It is a colourless deliquescent solid made by sulfonation of benzene, C6H5SO2OH,m.p. 43–44°C, usually found as an oily liquid. It is made by treating benzene with concentrated sulphuric acid, and Its alkyl derivatives are used as detergents. Any further substitution onto the benzene ring is directed into the 3 position.
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.
Deliquescent needles or large plates.
Slightly soluble in water.
Benzenesulfonic acid reacts with bases and many organic compounds. Benzenesulfonic acid has the characteristic reactions of a strong aromatic sulfonic acid. Acid hydrolysis at 175 ℃ splits it into benzene and sulfuricacid. Additional sulfonation with fuming sulfuric acid gives 1,3-benzenedisulfonic acid, which reacts further to 1,3,5-benzenetrisulfonic acid, and also diphenyl sulfone disulfonic acid.
Benzenesulfonic acid reacts with benzene to form diphenyl sulfone according to a Friedel – Crafts-type reaction.
Benzenesulfonic acid reacts with alkali metal hydroxide at 320 – 350 ℃ to form sodium phe- nolate. This reaction was used in the first industrial synthesis of phenol.
Flash point data for Benzenesulfonic acid are not available, however Benzenesulfonic acid is probably combustible.
Flammability and Explosibility
Non flammable
Poison by ingestion,
sbn contact, and probably inhalation. A
severe skin and eye irritant. See also
SULFATES and SULFONATES.
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.]
Benzenesulfonic acid is biologically degradable. If the desired benzenesulfonic acid can be precipitated from sulfuric acid solution without salt being added, the spent acid can be upgraded in a sulfuric acid recovery plant. If the wastewater contains salts and nondegradable sulfonic acids, low-pressure wet oxidation is a possible method of treatment that subsequently allows effective degradation in wastewater treatment works.
