Chiral Pyrrolidinium Ionic Liquids with (−)‐Borneol Fragment in the Cation – Synthesis, Physicochemical Properties and Application in Diels‐Alder Reaction

Abstract

AbstractA series of chiral pyrrolidinium salts containing (1 S)‐endo‐(−)‐born‐2‐yloxymethyl substituent in the structure of the cation and six different anions: chloride, tetrafluoroborate [BF4]−, hexafluorophosphate [PF6]−, trifluoromethanesulfonate [OTf]−, bis(trifluoromethylsulfonyl)imide [NTf2]−, bis(pentafluoroethylsulfonyl)imide [NPf2]− and perfluorobutanesulfonate [C4FS]− were efficiently prepared and extensively characterized. The enantiomeric purity of them was confirmed by NMR analysis with a chemical shift reagent. All salts were characterized with the specific rotation, the solubility in commonly used solvents, thermal properties, including phase transition temperatures and thermal stability. Salts with [PF6]−, [C4FS]−, [NTf2]− and [NPf2]− anions were classified as chiral ionic liquids (CILs). Moreover, salts with [NTf2]− and [NPf2]− anions were in the liquid state at room temperature and below. Therefore, density and dynamic viscosity, the surface tension and the contact angle on three different surfaces were also measured for them. Additionally, these chiral ionic liquids were tested as solvents in Diels‐Alder reaction.