Triethyloxonium tetrafluoroborate is the
organic
Organic may refer to:
* Organic, of or relating to an organism, a living entity
* Organic, of or relating to an anatomical organ
Chemistry
* Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
oxonium compound with the formula
3CH2)3O">CH3CH2)3OF
4. It is often called Meerwein's reagent or Meerwein's salt after its discoverer
Hans Meerwein
Hans Meerwein (May 20, 1879 in Hamburg, Germany – October 24, 1965 in Marburg, Germany) was a German chemist.
Several reactions and reagents bear his name, most notably the Meerwein–Ponndorf–Verley reduction, the Wagner–Meerwein rearr ...
. Also well known and commercially available is the related
trimethyloxonium tetrafluoroborate
Trimethyloxonium tetrafluoroborate is the organic compound with the formula . (It is sometimes called "Meerwein's salt" after Hans Meerwein.Meerwein's salt classically referred to triethyloxonium tetrafluoroborate. However, in recent years, the t ...
. The compounds are white solids that dissolve in polar organic solvents. They are strong
alkylating agent
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effectin ...
s. Aside from the
salt, many related derivatives are available.
Synthesis and reactivity
Triethyloxonium tetrafluoroborate is prepared from
boron trifluoride,
diethyl ether
Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable li ...
and
epichlorohydrin:
: 4 Et
2O·BF
3 + 2 Et
2O + 3 C
2H
3(O)CH
2Cl → 3 Et
3O
+ + B
2Cl)CH2OEt">OCH(CH2Cl)CH2OEtsub>3
The trimethyloxonium salt is available from
dimethyl ether
Dimethyl ether (DME; also known as methoxymethane) is the organic compound with the formula CH3OCH3,
(sometimes ambiguously simplified to C2H6O as it is an isomer of ethanol). The simplest ether, it is a colorless gas that is a useful precursor ...
via an analogous route. These salts do not have long shelf-lives at room temperature. They degrade by hydrolysis:
:
3CH2)3O">CH3CH2)3Osup>+ + H
2O → (CH
3CH
2)
2O + CH
3CH
2OH +
HBF4
The propensity of trialkyloxonium salts for alkyl-exchange can be advantageous. For example, trimethyloxonium tetrafluoroborate, which reacts sluggishly due to it low solubility in most compatible solvents may be converted in situ to higher alkyl/more soluble oxoniums, thereby accelerating alkylation reactions.
Structure
The structure of triethyloxonium tetrafluoroborate has not been characterized by
X-ray crystallography, but the structure of triethyloxonium
hexafluorophosphate
Hexafluorophosphate is an anion with chemical formula of . It is an octahedral species that imparts no color to its salts. is isoelectronic with sulfur hexafluoride, , and the hexafluorosilicate dianion, , and hexafluoroantimonate . In this an ...
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.
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.
References
{{Tetrafluoroborates
Reagents for organic chemistry
Tetrafluoroborates
Ethylating agents
Oxonium compounds