Triethyloxonium tetrafluoroborate

Triethyloxonium tetrafluoroborate
IUPAC name Triethyloxonium tetrafluoroborate
Identifiers
CAS number	368-39-8 Y
PubChem	2723982
ChemSpider	2006158 N
UN number	3261
Beilstein Reference	3598090
Jmol-3D images	Image 1
SMILES F[B-](F)(F)F.CC[O+](CC)CC
InChI InChI=1S/C6H15O.BF4/c1-4-7(5-2)6-3;2-1(3,4)5/h4-6H2,1-3H3;/q+1;-1 N Key: IYDQMLLDOVRSJJ-UHFFFAOYSA-N N
Properties
Molecular formula	C6H15BF4O
Molar mass	189.99 g mol−1
Exact mass	190.115208388 g mol-1
Melting point	91-92 °C, 364-365 K, 196-198 °F
Solubility in water	Reacts
Hazards
EU classification	C
R-phrases	R14, R34
S-phrases	S22, S26, S36/37/39
N tetrafluoroborate (verify) (what is: Y/N?) Except where noted otherwise, 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 [(CH₃CH₂)₃O]BF₄. It is often called Meerwein's reagent after its discoverer Hans Meerwein.^[1] 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.^[2]

Synthesis

Triethyloxonium tetrafluoroborate is prepared from boron trifluoride, diethyl ether, and epichlorohydrin:^[3]

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.^[4] These salts do not have long shelf-lives at room temperature. These salts degrade by hydrolysis:

[(CH₃CH₂)₃O]⁺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.^[5]

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. 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. 
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", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv5p1080 ; Coll. Vol. 5: 1080 
4. ^ T. J. Curphey (1988), "Trimethyloxonium tetrafluoroborate", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV6P1019 ; Coll. Vol. 6: 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.