Sulfonate

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.

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:

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:

ArSO₃Na + NaOH → ArONa + Na₂SO₃

This route is employed commercially to produce ethylphenol from ethylbenzene.

Uses and occurrences

Sulfonates

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.

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. 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.

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.
• Nosylate (o- or p-nitrobenzenesulfonate), o- or p-O₂N−C₆H₄−SO−3