Triethyloxonium tetrafluoroborate
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| Template:Longitem | 3598090 |
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| UN number | 3261 |
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Triethyloxonium tetrafluoroborate is the organic oxonium compound with the formula Template:Chem2. It is often called Meerwein's reagent or Meerwein's salt after its discoverer Hans Meerwein.[1][2] Also well known and commercially available is the related trimethyloxonium tetrafluoroborate. The compounds are white solids that dissolve in polar organic solvents. They are strong alkylating agents. Aside from the [[tetrafluoroborate|Template:Chem2]] salt, many related derivatives are available.[3]
Synthesis and reactivity
Triethyloxonium tetrafluoroborate is prepared from boron trifluoride, diethyl ether, and epichlorohydrin:[4]
where the Et stands for ethyl. The trimethyloxonium salt is available from dimethyl ether via an analogous route.[5] These salts do not have long shelf-lives at room temperature. They degrade by hydrolysis:
The propensity of trialkyloxonium salts for alkyl-exchange can be advantageous. For example, trimethyloxonium tetrafluoroborate, which reacts sluggishly due to its low solubility in most compatible solvents, may be converted in situ to higher alkyl/more soluble oxoniums, thereby accelerating alkylation reactions.[6]
This reagent is useful for esterification of carboxylic acids under conditions where acid-catalyzed reactions are infeasible: [7]
Structure
The structure of triethyloxonium tetrafluoroborate has not been characterized by X-ray crystallography, but the structure of triethyloxonium hexafluorophosphate has been examined. The measurements confirm that the cation is pyramidal with C–O–C angles in the range 109.4°–115.5°. The average C–O distance is 1.49 Å.[8]
Safety
Triethyloxonium tetrafluoroborate is a very strong alkylating agent, although the hazards are diminished because it is non-volatile. It releases strong acid upon contact with water. The properties of the methyl derivative are similar.
References
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- ↑ Hartwig Perst, Dave G. Seapy "Triethyloxonium Tetrafluoroborate" in Encyclopedia of Reagents for Organic Synthesis John Wiley & Sons, New York, 2008. Script error: No such module "CS1 identifiers".. Article Online Posting Date: March 14, 2008
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