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Triethyloxonium tetrafluoroborate

Names
IUPAC name Triethyloxonium tetrafluoroborate
Identifiers
CAS Number	368-39-8
ECHA InfoCard	100.006.096
CompTox Dashboard (EPA)	DTXSID20883372
Properties
Chemical formula	C6H15BF4O
Molar mass	189,99 g/mol
Melting point	91–92 °C
Boiling point	dec.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Infobox references

Triethyloxonium tetrafluoroborate is the organic oxonium compound with the formula BF₄. It is often called Meerwein's reagent after its discoverer Hans Meerwein. Also well known and commercially available is the related trimethyloxonium tetrafluoroborate. The compounds are exceptionally strong alkylating agents. Aside from the BF₄ salt, many related derivatives are available with varying solubilities and stabilities.

Synthesis

Triethyloxonium tetrafluoroborate is prepared from boron trifluoride, diethyl ether, and epichlorohydrin:

4 Et₂O·BF₃ + 2 Et₂O + 3 C₂H₃(O)CH₂Cl → 3 Et₃OBF₄ + B₃

The trimethyloxonium salt is available from dimethyl ether via an analogous route. These salts do not have long shelf-lives at room temperature. These salts degrade by hydrolysis:

BF₄ + H₂O → (CH₃CH₂)₂O + CH₃CH₂OH + HBF₄

The propensity of trialkyloxoniums to undergo alkyl-exchange may be utilized to the chemists' advantage. For example, trimethyloxonium tetrafluoroborate, which reacts sluggishly due to low solubility in most compatible solvents may be converted in-situ to higher alkyl/more soluble oxoniums, thereby speeding up alkylation reactions.

Structure

The compound features pyramidal oxonium cation and a tetrahedral fluoroborate anion. Reflecting its ionic character, the salt dissolves in polar but inert solvents such as dichloromethane, sulfur dioxide, and nitromethane.

Safety

Triethyloxonium tetrafluoroborate is a 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.

Use

Alkylating agent for nucleophilic functional groups in organic synthesis.

References

1. H. Meerwein, G. Hinz, P. Hofmann, E. Kroning, and E. Pfeil (1937). "Über Tertiäre Oxoniumsalze, I". Journal für Praktische Chemie. 147 (10–12): 257. doi:10.1002/prac.19371471001.{{cite journal}}: CS1 maint: multiple names: authors list (link)H. Meerwein, E. Bettenberg, H. Gold, E. Pfeil, and G. Willfang (1940). "Über Tertiäre Oxoniumsalze, II". Journal für Praktische Chemie. 154 (3–5): 83. doi:10.1002/prac.19391540305.{{cite journal}}: CS1 maint: multiple names: authors list (link)
2. Hartwig Perst, Dave G. Seapy "Triethyloxonium Tetrafluoroborate" in Encyclopedia of Reagents for Organic Synthesis John Wiley & Sons, New York, 2008. doi:10.1002/047084289X.rt223.pub2. Article Online Posting Date: March 14, 2008
3. H. Meerwein (1973). "Triethyloxonium fluoroborate". Organic Syntheses; Collected Volumes, vol. 5, p. 1080.
4. T. J. Curphey (1988). "Trimethyloxonium tetrafluoroborate". Organic Syntheses; Collected Volumes, vol. 6, p. 1019.
5. Vartak A.P. and Crooks P.A. (2009). "A Scalable Enantioselective synthesis of the alpha2-adrenergic Agonist, Lofexidine". Org. Process. Res. Dev. 13 (3): 415–419. doi:10.1021/op8002689.

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