Inorganosulfur chemistry, asulfonate is asalt oranion of asulfonic acid. The formula for thisfunctional group isRSO−3. Sulfonates are theconjugate bases of sulfonic acids. Sulfonates are generally stable in water, non-oxidizing, and colorless. Many useful compounds and even some biochemicals are sulfonates. Most detergents and surfactants are sulfonates. These includealkylbenzene sulfonates, 𝛼-olefin sulfonates, and paraffin sulfonates.[1]
Sulfonates are generally prepared by deprotonation (neutralization) of sulfonic acids. Because sulfonic acids arestrong acids, they spontaneously convert to sulfonates when dissolved in water:RSO3H → RSO−3 + H+To isolate sulfonate salts, these solutons are treated with base:RSO3H + NaOH → RSO3Na + H2O
Classically, alkylsulfonates can prepared by theStrecker sulfite alkylation,[2] in whichsulfite displaces ahalide:[3]
Arylsulfonates are produced by sulfonation of the arene usingsulfur trioxide,sulfuric acid, or related reagents, followed by deprotonation of the resulting acid:[4]
Alkyl and arylsulfonates also arise by hydrolysis ofsulfonyl chlorides:[5]
The structure of many sulfonate salts (and esters and acids) have been verified byX-ray crystallography. The sulfur site at the center of a tetrahedron, with three oxygen and a carbon at the vertices. For the salts, the S-O distances are near 144picometers in length. Crystals typically containwater of crystallization, reflecting the highly ionic nature of these salts.[6]
Being weakly basic, sulfonate salts are poor nucleophiles. Their alkylation requires strongly electrophilic alkylating agents. Sulfonates react withphosphorus pentachloride and related chlorinating agents to give the sulfonyl chloride:[7]
Arylsulfonates undergo hase hydrolysis to give (after acidic workup) phenols. This route (ArH to ArSO3H to ArOH) was once a major route to phenols. This reaction, calledalkaline fusion, requires temperatures in the 200-300 °C range:[8][9]
This route is employed commercially to produceethylphenol fromethylbenzene.[10]
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Sulfonate salts are widely used surfactants and detergents. Alkylbenzenesulfonates are detergents found inshampoos,toothpaste,laundry detergent,dishwashing liquid, etc. They are also used asion exchange resins.
Lignosulfonates (LS's) are derived from lignin, an abundant waste product frompapermaking that is otherwise burned as fuel. LS's are water-soluble anionicpolyelectrolytes that are mainly used asDispersants but have many niche applications.[11] In thesulfite process for paper-making, lignin is removed from the lignocellulose by treating wood chips with solutions of sulfite and bisulfite ions. These reagents cleave the bonds between the cellulose and lignin components as well as C-O bonds within the lignin itself.
Some alkylsulfonates occur naturally.Taurine (2-aminoethanesulfonate) is widely distributed in mammalian tissues, as well as a component ofRed Bull energy drinks.Coenzyme-M (2-mercaptoethanesulfonic acid) is the methyl-carrying cofactor inmethanogenesis.
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