Sulfonate

The sulfonate ion.

For Sulfonate ester, see Sulfonate ester.

In organosulfur chemistry, a sulfonate is a salt or anion of a sulfonic acid. The formula for this functional group is RSO−3. Sulfonates are the conjugate 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 include alkylbenzene sulfonates, 𝛼-olefin sulfonates, and paraffin sulfonates. ^[1]

Preparation

Sulfonates are generally prepared by deprotonation (neutralization) of sulfonic acids. Because sulfonic acids are strong 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 the Strecker sulfite alkylation, ^[2] in which sulfite displaces a halide: ^[3]

RBr + Na₂SO₃ → RSO₃Na + NaBr

Arylsulfonates are produced by sulfonation of the arene using sulfur trioxide, sulfuric acid, or related reagents, followed by deprotonation of the resulting acid: ^[4]

ArH + H₂SO₄ → ArSO₃H + H₂O

ArSO₃H + NaOH → ArSO₃Na + H₂O

Alkyl and arylsulfonates also arise by hydrolysis of sulfonyl chlorides: ^[5]

RSO₂Cl + NaOH → ArSO₃Na + NaCl

Structure

The structure of many sulfonate salts (and esters and acids) have been verified by X-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 144 picometers in length. Crystals typically contain water of crystallization, reflecting the highly ionic nature of these salts. ^[6]

Reactions

Being weakly basic, sulfonate salts are poor nucleophiles. Their alkylation requires strongly electrophilic alkylating agents. Sulfonates react with phosphorus pentachloride and related chlorinating agents to give the sulfonyl chloride: ^[7]

RSO₃Na + PCl₅ → RSO₂Cl + POCl₃ + NaCl

Alkaline fusion

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, called alkaline fusion, requires temperatures in the 200-300 °C range: ^{[8] [9]}

ArSO₃Na + NaOH → ArONa + Na₂SO₃

This route is employed commercially to produce ethylphenol from ethylbenzene. ^[10]

Uses and occurrences

Sulfonates

• 
  sodium alkylbenzene sulfonate
• 
  taurine
• 
  Coenzyme M
• 
  perfluorooctanesulfonate, an "everwhere chemical"
• 
  Allura Red AC, a red dye, was once used in foods
• 
  Acamprosate calcium for treating alcohol use disorder

Sulfonate salts are widely used surfactants and detergents. Alkylbenzenesulfonates are detergents found in shampoos, toothpaste laundry detergent, dishwashing liquid, etc. They are also used as ion exchange resins.

Water softening usually involves removal of calcium ions in water using a sulfonated ion-exchange resin.

Lignosulfonates (LS's) are derived from lignin, an abundant waste product from papermaking that is otherwise burned as fuel. LS's are water-soluble anionic polyelectrolytes that are mainly used as Dispersants but have many niche applications. ^[11] In the sulfite 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.

idealized scheme for lignin depolymerization by the Sulfite process.

Some alkylsulfonates occur naturally. Taurine (2-aminoethanesulfonate) is widely distributed in mammalian tissues, as well as a component of Red Bull energy drinks. Coenzyme-M (2-mercaptoethanesulfonic acid) is the methyl-carrying cofactor in methanogenesis.

Examples

• Mesylate (methanesulfonate), CH₃−SO−3
• Triflate (trifluoromethanesulfonate), CF₃−SO−3
• Ethanesulfonate (esilate, esylate), CH₃CH₂−SO−3
• Tosylate (p-toluenesulfonate), p-CH₃−C₆H₄−SO−3
• Benzenesulfonate (besylate), C₆H₅−SO−3
• Closilate (closylate, chlorobenzenesulfonate), Cl−C₆H₄−SO−3
• Camphorsulfonate (camsilate, camsylate), (C₁₀H₁₅O)−SO−3
• Pipsylate (p-iodobenzenesulfonate derivative), p-I−C₆R₄−SO−3, where R is any group. ^[12]
• Nosylate (o- or p-nitrobenzenesulfonate), o- or p-O₂N−C₆H₄−SO−3

See also

• Sulfate
• Sulfoxide
• Sulfonyl

References

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2. Adolf Strecker (1868). "Ueber eine neue Bildungsweise und die Constitution der Sulfosäuren" (PDF). Annalen der Chemie und Pharmacie . 148 (1): 90–96. doi:10.1002/jlac.18681480108.
3. C. S. Marvel, M. S. Sparberg (1930). "Sodium 2-Bromoethanesulfonate". Organic Syntheses. 10: 96. doi:10.15227/orgsyn.010.0096.
4. Louis F. Fieser (1936). "2- and 3-Phenanthrenesulfonic Acids". Organic Syntheses. 16: 63. doi:10.15227/orgsyn.016.0063.
5. E. Wertheim (1935). "Orthanilic Acid". Organic Syntheses. 15: 55. doi:10.15227/orgsyn.015.0055.
6. Arshad, Muhammad Nadeem; Tahir, M. Nawaz; Khan, Islam Ullah; Shafiq, Muhammad; Siddiqui, Waseeq Ahmad (2008). "Sodium 2-iodobenzenesulfonate monohydrate". Acta Crystallographica Section e Structure Reports Online. 64 (12): m1628. doi:10.1107/S1600536808039202. PMC   2960107 . PMID   21581218.
7. Roger Adams, C. S. Marvel, H. T. Clarke, G. S. Babcock, T. F. Murray (1921). "Benzenesulfonyl Chloride". Organic Syntheses. 1: 21. doi:10.15227/orgsyn.001.0021.
8. W. W. Hartman (1923). "p-Cresol". Organic Syntheses. 3: 37. doi:10.15227/orgsyn.003.0037.
9. Arthur W. Weston, C. M. Suter (1941). "3,5-Dihydroxybenzoic Acid". Organic Syntheses. 21: 27. doi:10.15227/orgsyn.021.0027.
10. Fiege, Helmut; Voges, Heinz-Werner; Hamamoto, Toshikazu; Umemura, Sumio; Iwata, Tadao; Miki, Hisaya; Fujita, Yasuhiro; Buysch, Hans-Josef; Garbe, Dorothea; Paulus, Wilfried (2000). "Phenol Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a19_313. ISBN   978-3-527-30385-4.
11. Lebo, Stuart E. Jr.; Gargulak, Jerry D.; McNally, Timothy J. (2015). "Lignin". Kirk-Othmer Encyclopedia of Chemical Technology. Kirk‑Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, Inc. pp. 1–26. doi:10.1002/0471238961.12090714120914.a01.pub3. ISBN   978-0-471-23896-6.
12. Beisler, J. A.; Sato, Y. (1971). "Chemistry of carpesterol, a novel sterol from Solanum xanthocarpum". The Journal of Organic Chemistry. 36 (25): 3946–3950. doi:10.1021/jo00824a022. ISSN   0022-3263. PMID   5127991.