methyl trifluoromethanesulfonate
{{chembox
| Watchedfields = changed
| verifiedrevid = 472646274
| ImageFile_Ref = {{chemboximage|correct|??}}
| ImageFile = StructureMeOTf.svg
| ImageSize = 180px
| ImageName = Structural formula of methyl triflate
| ImageFile1 = Methyl-triflate-3D-balls.png
| ImageName1 = Ball-and-stick model of methyl triflate
| PIN = Methyl trifluoromethanesulfonate
| OtherNames = Trifluoromethanesulfonic acid, methyl ester
Triflic acid, methyl ester, methyl triflate
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 333-27-7
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 9153
| EC_number = 206-371-7
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 7B25Z22EPV
| RTECS =
| PubChem = 9526
| UNNumber = 2924
| SMILES = COS(=O)(=O)C(F)(F)F
| InChI = 1/C2H3F3O3S/c1-8-9(6,7)2(3,4)5/h1H3
| InChIKey = OIRDBPQYVWXNSJ-UHFFFAOYAL
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C2H3F3O3S/c1-8-9(6,7)2(3,4)5/h1H3
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = OIRDBPQYVWXNSJ-UHFFFAOYSA-N
}}
|Section2={{Chembox Properties
| C=2|H=3|F=3|O=3|S=1
| Appearance = Colourless Liquid
| Density = 1.496 g/mL
| Solubility = Hydrolyzes
| MeltingPtC = −64
| BoilingPtC = 100
| pKa =
| pKb =
}}
|Section3={{Chembox Structure
| Dipole =
}}
|Section7={{Chembox Hazards
| ExternalSDS =
| MainHazards = Corrosive
| FlashPtC = 38
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|226|301|311|314|330}}
| PPhrases = {{P-phrases|210|233|380|303+361+353|304+340+310|305+351+338}}
}}
|Section8={{Chembox Related
| OtherCompounds = Methyl fluorosulfonate
}}
}}
Methyl trifluoromethanesulfonate, also commonly called methyl triflate and abbreviated MeOTf, is the organic compound with the formula {{chem2|CF3SO2OCH3}}. It is a colourless liquid which finds use in organic chemistry as a powerful methylating agent.{{cite journal|first1=Roger W.|last1=Alder|first2=Justin G. E.|last2=Phillips|author3=Huang Lijun|author4=Huang Xuefei|ref={{harvid|Alder|Phillips|Huang|Huang|2005}}|title=Methyltrifluoromethanesulfonate|journal=Encyclopedia of Reagents for Organic Synthesis|year=2005|doi=10.1002/047084289X.rm266m.pub2|isbn=0471936235}} The compound is closely related to methyl fluorosulfonate ({{chem2|FSO2OCH3}}). Although there has yet to be a reported human fatality, several cases were reported for methyl fluorosulfonate (LC50 (rat, 1 h) = 5 ppm), and methyl triflate is expected to have similar toxicity based on available evidence.{{cite magazine|last1=Alder|first1=R. W.|first2=M. L.|last2=Sinnott|first3=M. C.|last3=Whiting|first4=D. A.|last4=Evans|author-link4=David A. Evans|title=Hazards of powerful methylating agents|magazine=Chemistry in Britain|volume=14|issue=7|year=1978|page=324}} Miscited as ——— (1976) Chem. Eng. News, vol. 54, no. 36, p. 56 in {{harvnb|Alder|Phillips|Huang|Huang|2005}}{{Verification needed|reason=Hard paywall for non-RSC members|date=December 2021}}
Synthesis
Methyl triflate is commercially available, however it may also be prepared in the laboratory by using dimethyl sulfate to methylate triflic acid.{{cite journal|last1=Stang|first1=Peter J.|last2=Hanack|first2=Michael|last3=Subramanian|first3=L. R.|title=Perfluoroalkanesulfonic Esters: Methods of Preparation and Applications in Organic Chemistry|journal=Synthesis|volume=1982|issue=2|year=1982|pages=85–126|issn=0039-7881|doi=10.1055/s-1982-29711}}
:{{chem2|CF3SO2OH + (CH3O)2SO2 → CF3SO2OCH3 + CH3OSO2OH}}
Reactivity
=Hydrolysis=
Upon contact with water, methyl triflate loses its methyl group, forming triflic acid and methanol:
:{{chem2|CF3SO2OCH3 + H2O → CF3SO2OH + CH3OH}}
=Methylation=
One ranking of methylating agents is {{chem2|(CH3)3O+ > CF3SO2OCH3 ≈ FSO2OCH3 > (CH3)2SO4 > CH3I}}. Methyl triflate will alkylate many functional groups which are very poor nucleophiles such as aldehydes, amides, and nitriles. It does not methylate benzene or the bulky 2,6-di-tert-butylpyridine. Its ability to methylate N-heterocycles is exploited in certain deprotection schemes.{{OrgSynth|author=Albert I. Meyers|author-link=Albert I. Meyers|author2=Mark E. Flanagan|name-list-style=amp|year=1998|title=2,2′-Dimethoxy-6-formylbiphenyl|volume=|pages= |collvol=9|collvolpages=258|prep=CV9P0258}}
= Cationic polymerization =
Methyl triflate initiates the living cationic polymerization of lactide{{Cite journal|last1=Rangel|first1=Irma|last2=Ricard|first2=Michèle|last3=Ricard|first3=Alain|date=1994|title=Polymerization of L-lactide and ε-caprolactone in the presence of methyl trifluoromethanesulfonate|journal=Macromolecular Chemistry and Physics|volume=195|issue=9|pages=3095–3101|doi=10.1002/macp.1994.021950908}} and other lactones including β-propiolactone, ε-caprolactone and glycolide.{{Cite journal|last1=Jonté|first1=J. Michael|last2=Dunsing|first2=Ruth|last3=Kricheldorf|first3=Hans R.|date=1985|title=Polylactones. 4. Cationic Polymerization of Lactones by Means of Alkylsulfonates|journal=Journal of Macromolecular Science: Part A - Chemistry|language=en|volume=22|issue=4|pages=495–514|doi=10.1080/00222338508056616|issn=0022-233X}}
File:Kationische_Polymerisation_von_Caprolacton_mit_Methyltriflat.svgCyclic carbonates like trimethylene carbonate and neopentylene carbonate (5,5-dimethyl-1,3-dioxan-2-one) can be polymerized to the corresponding polycarbonates.{{Cite journal|last1=Kricheldorf|first1=Hans R.|last2=Weegen-Schulz|first2=Bettina|last3=Jenssen|first3=Jörg|date=1998|title=Cationic polymerization of aliphatic cyclocarbonates|journal=Macromolecular Symposia|language=en|volume=132|issue=1|pages=421–430|doi=10.1002/masy.19981320139}} 2-alkyl-2-oxazolines, for example 2-ethyl-2-oxazoline, are also polymerized to poly(2-alkyloxazoline)s.{{Cite journal|last1=Glassner|first1=Mathias|last2=D’hooge|first2=Dagmar R.|last3=Young Park|first3=Jin|last4=Van Steenberge|first4=Paul H.M.|last5=Monnery|first5=Bryn D.|last6=Reyniers|first6=Marie-Françoise|last7=Hoogenboom|first7=Richard|date=2015|title=Systematic investigation of alkyl sulfonate initiators for the cationic ring-opening polymerization of 2-oxazolines revealing optimal combinations of monomers and initiators|journal=European Polymer Journal|language=en|volume=65|pages=298–304|doi=10.1016/j.eurpolymj.2015.01.019|hdl=1854/LU-5924229|url=https://biblio.ugent.be/publication/5924229|hdl-access=free}}
Applications
= Radiochemistry =
Carbon-11 methyl triflate ([11C]MeOTf{{Cite journal |last=Jewett |first=D. M. |date=1992 |title=A simple synthesis of [11C]methyl triflate |url=https://pubmed.ncbi.nlm.nih.gov/1333459/ |journal=International Journal of Radiation Applications and Instrumentation, Part A |volume=43 |issue=11 |pages=1383–1385 |doi=10.1016/0883-2889(92)90012-4 |issn=0883-2889 |pmid=1333459|hdl=2027.42/29777 |hdl-access=free }}), or methyl triflate containing the carbon-11 isotope, is commonly used in radiochemistry to synthesize radioactively labeled compounds that can be traced in living organisms using positron emission tomography (PET). For example, [11C]MeOTf has been used extensively in the production of Pittsburgh Compound B, which first allowed β-amyloid plaques to be imaged in a living brain.