Meerwein salt
Encyclopedia
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
. 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.
, diethyl ether
, and epichlorohydrin
:
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:
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.
, sulfur dioxide
, and nitromethane
.
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
oxonium
Oxonium ion
The oxonium ion in chemistry is any oxygen cation with three bonds. The simplest oxonium ion is the hydronium ion H3O+. Another oxonium ion frequently encountered in organic chemistry is obtained by protonation or alkylation of a carbonyl group e.g...
compound with the formula [(CH3CH2)3O]BF4. It is often called Meerwein's reagent after its discoverer Hans Meerwein
Hans Meerwein
Hans Meerwein was a German chemist.His name is present in the names of several reactions and reagents, for example the Meerwein-Ponndorf-Verley reduction, the Wagner-Meerwein rearrangement...
. Also well known and commercially available is the related trimethyloxonium tetrafluoroborate
Trimethyloxonium tetrafluoroborate
Trimethyloxonium tetrafluoroborate is a methylating agent. It is the methyl analog to triethyloxonium tetrafluoroborate. Commercially available, this compound is prepared similarly, by reaction of boron trifluoride etherate with dimethyl ether and epichlorohydrin....
. 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 trifluorideBoron trifluoride
Boron trifluoride is the chemical compound with the formula BF3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...
, diethyl ether
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...
, and epichlorohydrin
Epichlorohydrin
Epichlorohydrin is an organochlorine compound and an epoxide. This is a colorless liquid with a pungent, garlic-like odor, moderately soluble in water, but miscible with most polar organic solvents. Epichlorohydrin is a highly reactive compound and is used in the production of glycerol, plastics,...
:
- 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
Dimethyl ether
Dimethyl ether , also known as methoxymethane, is the organic compound with the formula . The simplest ether, it is a colourless gas that is a useful precursor to other organic compounds and an aerosol propellant. When combusted, DME produces minimal soot and CO, though HC and NOx formation is...
via an analogous route. These salts do not have long shelf-lives at room temperature. These salts degrade by hydrolysis:
- [(CH3CH2)3O]+BF4− + H2O → (CH3CH2)2O + CH3CH2OH + HBF4Fluoroboric acidFluoroboric acid is the chemical compound with the formula HBF4. It is the conjugate acid of tetrafluoroborate. It is available commercially as a solution in water and other solvents such as diethyl ether...
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 dichloromethaneDichloromethane
Dichloromethane is an organic compound with the formula CH2Cl2. This colorless, volatile liquid with a moderately sweet aroma is widely used as a solvent. Although it is not miscible with water, it is miscible with many organic solvents...
, sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
, and nitromethane
Nitromethane
Nitromethane is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a slightly viscous, highly polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent...
.