Trimethylsulfoxonium Iodide

(X = I) [1774-47-6] C3H9IOS (MW 220.07) InChI = 1S/C3H9OS.HI/c1-5(2,3)4;/h1-3H3;1H/q+1;/p-1 InChIKey = BPLKQGGAXWRFOE-UHFFFAOYSA-M (X = Cl) [5034-06-0] C3H9ClOS (MW 128.62) InChI = 1S/C3H9OS.ClH/c1-5(2,3)4;/h1-3H3;1H/q+1;/p-1 InChIKey = KQYWHJICYXXDSQ-UHFFFAOYSA-M (precursor of dimethylsulfoxonium methylide,1 which transfers a methylene group to ketones and aldehydes to form epoxides and to α,β-unsaturated carbonyl compounds to produce cyclopropyl derivatives;1-3 a methylation reagent;4 can function as a catalyst5) Physical Data: trimethylsulfoxonium iodide: mp 170 °C (dec), Aldrich Catalog: mp 208–212 °C (dec.), Belstein: mp 220 °C (dec.),13, 19, 20 yellow crystalline powder; trimethylsulfoxonium chloride: 227 °C (subl), Belistein: mp 222–223 °C,10 Aldrich Catalog: mp 226–229 °C, white powder. The vibrational spectra of both iodide and chloride salts, as well as NMR studies of molecular motion of both salts, have been investigated.6-8 pKa = 18.2 for sulfoxonium ion in DMSO. Solubility: trimethylsulfoxonium iodide: 3.85 g/100 g H2O (20 °C).9 Trimethylsulfoxonium chloride has greater solubility in THF than trimethylsulfoxonium iodide.10 Both sulfoxonium salts sol H2O, DMSO, t-butanol. Form Supplied in: both iodide and chloride salts are widely available in powder form. Analysis of Reagent Purity: the purity of trimethylsulfoxonium iodide and trimethylsulfoxonium chloride can be determined by an AgNO3 titration method. A miscible organic solvent, such as acetone, ethanol, or propanol, is usually adopted to carry out the titration process.11 For precise data, the AgNO3(aq) solution should be protected from light and stored in a dark glass bottle. Purification: trimethylsulfoxonium iodide and trimethylsulfoxonium chloride are precursors of dimethylsulfoxonium methylide. Except when used under phase transfer conditions, the sulfur ylide is usually prepared by deprotonation of trimethylsulfoxonium iodide or trimethylsulfoxonium chloride with moisture-sensitive strong bases such as Sodium Hydride, n‐Butyllithium, etc. Therefore drying the salts prior to use is crucial. Trimethylsulfoxonium iodide can be purified by recrystallization from H2O and dried in a desiccator over P2O5 before use.2, 9 Preparative Method: trimethylsulfoxonium iodide is commonly prepared by reaction of Dimethyl Sulfoxide with ∼2.5 equiv of Iodomethane.12 After refluxing for 24 h at 80 °C, the reaction mixture is cooled and the crude solid product filtered and washed with acetone to give the trimethylsulfoxonium iodide. Iodomethane has to be handled in a fume hood because of its high volatility and toxicity.12-14 Excess MeI is used to ensure the completion of the reaction. Trimethylsulfoxonium chloride can be obtained by the treatment of trimethylsulfoxonium iodide with benzyltributylammonium chloride in a mixed solvent system (CH2Cl2/H2O).10 The end point is reached when two clear phases are obtained. The aqueous phase is then washed with CH2Cl2. After evaporation of H2O, solid trimethylsulfoxonium chloride is obtained. Direct oxidation of trimethylsulfonium chloride with Sodium Hypochlorite in the presence of catalytic amount of Ruthenium(VIII) Oxide in H2O at room temperature also provides trimethylsulfoxonium chloride.15 Alternatively, trimethylsulfoxonium chloride can be synthesized by treating a hot aqueous solution of trimethylsulfoxonium iodide with AgCl. After removal of iodide salt, the aqueous filtrate is evaporated to dryness to give trimethylsulfoxonium chloride.6 Handling, Storage, and Precautions: both the iodide and chloride salts are hygroscopic and have to be stored in a cool, dry place. They are incompatible with strong oxidizing agents and strong base. The iodide salt is sensitive to light and needs to be protected from light as much as possible.