Ishikawa reagent
Encyclopedia
Ishikawa's reagent is a fluorinating reagent used in organic chemistry. It is used to convert alcohols into alkyl fluorides and carboxylic acids into acyl fluorides. Aldehydes and ketones do not react with it. The reagent consists of a mixture of N,N-diethyl-(1,1,2,3,3-hexafluoropropyl)amine and N,N-diethyl-(E)-pentafluoropropenylamine in varying proportions. The active species is the hexafluoropropylamine; any enamine
is converted into this by the hydrogen fluoride
byproduct as the reaction proceeds.
Ishikawa's reagent is a popular alternative to the DAST reagent, since it is shelf-stable and easily prepared from inexpensive and innocuous reagents. It is an improvement on Yarovenko's reagent, the adduct of chlorotrifluoroethylene
and diethylamine
, which must be prepared in a sealed vessel and once prepared keeps only for a few days, even in the refrigerator.
The reagent is mostly used to convert primary alcohols to alkyl fluorides under mild conditions with high yield. However, secondary and tertiary alcohols give a substantial amount of alkenes and ethers as side products.
in ether
at 0 °C and distilling the product in vacuo. The amount of enamine in the product depends on temperature control during the reaction – the higher the temperature the more enamine.
Enamine
An enamine is an unsaturated compound derived by the reaction of an aldehyde or ketone with a secondary amine followed by loss of H2O.The word "enamine" is derived from the affix en-, used as the suffix of alkene, and the root amine. This can be compared with enol, which is a functional group...
is converted into this by the hydrogen fluoride
Hydrogen fluoride
Hydrogen fluoride is a chemical compound with the formula HF. This colorless gas is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the...
byproduct as the reaction proceeds.
Ishikawa's reagent is a popular alternative to the DAST reagent, since it is shelf-stable and easily prepared from inexpensive and innocuous reagents. It is an improvement on Yarovenko's reagent, the adduct of chlorotrifluoroethylene
Chlorotrifluoroethylene
CTFE, or chlorotrifluoroethylene is a chlorofluorocarbon with chemical formula CF2CClF. It is commonly used as a refrigerant in cryogenic applications. CTFE can be polymerised to produce the plastic ECTFE....
and diethylamine
Diethylamine
Diethylamine is a secondary amine with the molecular structure CH3CH2NHCH2CH3. It is a flammable, strongly alkaline liquid. It is miscible with water and ethanol. It is a colorless liquid which often appears brown due to impurities...
, which must be prepared in a sealed vessel and once prepared keeps only for a few days, even in the refrigerator.
The reagent is mostly used to convert primary alcohols to alkyl fluorides under mild conditions with high yield. However, secondary and tertiary alcohols give a substantial amount of alkenes and ethers as side products.
Synthesis
The compound is prepared by adding hexafluoropropene to a solution of diethylamineDiethylamine
Diethylamine is a secondary amine with the molecular structure CH3CH2NHCH2CH3. It is a flammable, strongly alkaline liquid. It is miscible with water and ethanol. It is a colorless liquid which often appears brown due to impurities...
in 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...
at 0 °C and distilling the product in vacuo. The amount of enamine in the product depends on temperature control during the reaction – the higher the temperature the more enamine.