Methyl Trifluoromethanesulfonate

Abstract

(R = CF3) [333-27-7] C2H3F3O3S (MW 164.12) InChI = 1/C2H3F3O3S/c1-8-9(6,7)2(3,4)5/h1H3 InChIKey = OIRDBPQYVWXNSJ-UHFFFAOYAL (R = F) [421-20-5] CH3FO3S (MW 114.11) InChI = 1/CH3FO3S/c1-5-6(2,3)4/h1H3 InChIKey = MBXNQZHITVCSLJ-UHFFFAOYAW (powerful methylating agents1, 2) Alternate Name: R = CF3, methyl triflate; R = F, Magic Methyl. Physical Data: methyl triflate: bp 99 °C, mp −64 °C, d 1.50 g cm−3. Methyl fluorosulfonate: bp 92 °C, mp −92.5 °C, d 1.45 g cm−3. Solubility: both reagents are miscible with all organic solvents, but react with many. They are only sl sol water, but hydrolyze rapidly as they dissolve. Useful inert solvents are CH2Cl2, SO2, sulfolane, nitromethane, Me2SO4, and Me3PO4. Form Supplied in: methyl triflate (MeOTf) is available as a colorless liquid. Methyl fluorosulfonate (MeOSO2F) was formerly available as Magic MethylTM but has been withdrawn (see below). Analysis of Reagent Purity: MeOTf gives a singlet in 1H NMR at δ 4.18, with 13C absorption at δ 61.60 and 119.32 (q), and a 19F shift of 75.4 ppm. MeOSO2F absorbs at δ 4.19 in 1H NMR (JHF; 0.4 Hz or less), with 13C absorption at δ 62.45, and a 19F shift of −31.2 ppm. 33S and 17O NMR data have been reported for both compounds.9 Preparative Methods: both reagents are prepared3, 4 by distilling an equimolar mixture of the corresponding acid with Dimethyl Sulfate in an all-glass apparatus with a short Vigreux column. They may be dried by standing over fused K2CO3 and redistillation. Trifluoromethanesulfonic Acid and Fluorosulfuric Acid are both available, and are comparably priced. Handling, Storage, and Precaution: both reagents are extremely hazardous. All possible precautions should be taken to avoid inhalation or absorption through the skin. A fatality has occurred with MeOSO2F through inhalation of the vapors leading to pulmonary edema.5 Dexamethasone isonicotinate (Auxiloson® spray) has been recommended as a first aid in the treatment of such pulmonary irritation.5 The oral LD50 of MeOSO2F is 112 mg/kg in mice, and an LC50 for 1 h exposure for rats between 5 and 6 ppm has been reported; severe eye irritation was noted.6 It is very unlikely7 that MeOTf is less dangerous, but no data on toxicity have been reported. Both materials are extremely destructive to the tissue of the mucous membranes and upper respiratory tract, eyes, and skin. Inhalation may be fatal as a result of spasm, inflammation, and edema of the larynx and bronchi, chemical pneumonitis, and pulmonary edema. Use in a fume hood. The reagents are stable in glass when dry, but storage of MeOSO2F in bottles with ground glass joints should be avoided as these slowly become fused. It is reported8 that MeOSO2F after storage over CaH2 for two weeks contained 17% Me2SO4.