Triethyloxonium tetrafluoroborate

white to light yellow crystal powder.

Triethyloxonium tetrafluoroborate is used as a powerful alkylating agent, especially for ethylation. It is used for the modification of carboxyl residues in proteins. It is involved in the preparation of μ-amino esters from lactams. It is also alkylating agent for nucleophilic functional groups in organic synthesis.

Triethyloxonium tetrafluoroborate can be used:
To prepare amino esters by reacting with lactams followed by hydrolysis.
In the preparation of substituted imidazolines from aziridines and nitriles via [3+2]-cycloaddition reaction.
For the N-alkylation of a series of N-arylsulfonyl-α-amino acid methyl esters having variable substituents at 4th position of the sulfonamide aromatic ring.
Synthesis of HDET2.

Triethyloxonium tetrafluoroborate is a powerful ethylating agent, although the hazards are diminished because it is non-volatile. It releases strong acid upon contact with water. When heated to decomposition it emits toxic vapors of boronand Fí. Mutation data reported.

Triethyloxonium tetrafluoroborate is prepared from boron trifluoride,diethyl ether and epichlorohydrin:
4 Et2O·BF3+ 2 Et2O + 3 C2H3(O)CH2Cl → 3 Et3O+BF4+ B[(OCH(CH2Cl)CH2OEt]3
The trimethyloxonium salt is available from dimethyl ether via an analogous route.These salts do not have long shelf-lives at room temperature. They degrade by hydrolysis:
[(CH3CH2)3O]+BF4+ H2O → (CH3CH2)2O + CH3CH2OH +HBF4

Crystallise it from diethyl ether. It is very hygroscopic, and must be handled in a dry box and stored at 0o. [Meerwein Org Synth Coll Vol V 1096 1973.] Pure material should give a clear and colourless solution in dichloromethane (1 in 50, w/v). [Beilstein 1 IV 1322.]