Recoverable Phase‐Transfer Catalysts with Fluorinated Anions: Generation and Reactions of Dichlorocarbene and CCl₃ Anion in the Heterogeneous System KOH(s)/CHCl₃/nBu₄NPF₆

Abstract

Tetraalkylammonium salts bearing PF6– and BF4– anions have been recognized as recoverable phase‐transfer catalysts for the synthesis of 1,1‐dichlorocyclopropane and α‐(trichloromethyl)carbinol derivatives from alkenes or aldehydes in the heterogeneous system KOH(s)/CHCl3. The catalysts retained their catalytic activity over several reactioncycles.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Ionic liquids containing the urea moiety for recognition of halides and complex anions

“…The unusual upfield shift of the urea protons when [Eumim]-OAc interacted with the halides promoted further investigation It has been reported that the charge densities on the F atoms of BF 4 -and PF 6 -are relative low and they only form weak hydrogen bonds with hydrogen bonding receptors [28]. Furthermore, BPh 4 -does not have an electronegative atom for hydrogen bonding with the receptor.…”

“…Furthermore, BPh 4 -does not have an electronegative atom for hydrogen bonding with the receptor. Therefore, both the charge density properties of BF 4 -, PF 6 -and BPh 4 -and the upfield shifts of the urea protons of the ionic liquids indicate that the dominate interaction between the anions and ionic liquid receptors is not hydrogen bonding.…”

“…1-Ethylurea-3-methylimidazolium acetate ([Eumim]OAc) was used as the receptor for the halides and complex anions (BF 4 -, PF 6 -, BPh 4 -). 1 H NMR spectra showed that the urea protons and imidazolium C (2) Anions such as fluoride, chloride, tetrafluoroborate, and hexafluorophate play a significant role in a wide range of environmental, biological and industrial processes [1][2][3][4]. Accordingly, the design and development of receptors for selective sensing or recognition of anions has attracted increasing interest.…”

“…Most anion receptors have hydrogen bond donating groups, such as amide [5,6], pyrrole [7,8], guanidinium [9], imidazolium [10,11], urea or thiourea [12,13], to recognize anions through the formation of hydrogen bonds. However, recognition of anions like BF 4 -, PF 6 -and BPh 4 -is difficult with this type of receptor because these anions have a poor ability to form hydrogen bonds.…”

“…In the present study, a series of imidazolium based ionic liquids containing the urea moiety were synthesized. The ionic liquids were used as receptors to recognize halides and complex anions, such as BF 4 -, PF 6 -and BPh 4 -, via the variation in the chemical shifts of the urea and imidazolium C(2) protons.…”