| The synthesis of benzimidazolium ionic liquids needs systematic research.In this paper,the systematic studies have been done.First,We synthesized ten ionic liquids:1-butyl-3-benzimidazolium bromide,1-octyl-3-benzimidazolium bromide,1-isooctyl-3-benzimidazolium bromide,1-butyl-3-octyl-benzimidazolium bromide,1,3-dibutyl-benzimidazolium bromide,1-butyl-3-isooctyl-benzimidazolium bromide,1,3-dioctyl-benzimidazolium bromide,1-octyl-3-isooctyl-benzimidazolium bromide,1-butyl-3-pyridyl-benzimidazolium bromide,and gemini ionic liquid[C4-6-C4bim]Br2.The synthesis steps of the benzimidazolium ionic liquids mentioned above were described in detail.In addition,1H NMR,FT-IR and mass spectrometry were used to characterize these new substances.Besides,The new single crystal[PdBr2· 2BBIm](CCDC:1541474)was grown to understand the extraction mechanism of the reaction between[HBBIm]Br and Pd(II)and the structure of complexes[PdBr2 · 2BBIm]was identified detailedly.For some of the benzimidazolium ionic liquids mentioned above,we investigated their extraction performance of precious metals.Firstly,we used ionic liquid 1-butyl-3-benzimidazolium bromide([HBBIm]Br)to extract and separate Pt and Pd.In this part,the effects of[HBBIm]Br concentration,initial metal concentration,sodium chloride,hydrochloric acid concentration and sodium nitrate concentration were studied in details.For the the extraction mechanisms,we have proved that the extraction mechanisms of noble metals Pt and Pd are different.The anion exchange mechanism between[HBBIm]Br and Pt was proved through Job’s method,FT-IR,and 1H NMR.The coordination mechanism between[HBBIm]Br and Pd was demonstrated by single X-ray diffraction,and became more robust with the support of ab initio quantum-chemical studies.we used ionic liquid[HBBIm]Br to separate and recycle high purity of Pt and Pd in one step.This work enriches the separation methods for noble metals Pt and Pd.We also studied the extraction performance of gold from N,N’-dialkylbenzimidazolium ionic liquids,and used similar methods to study the effect factors of Au extraction and the extraction mechanisms.We directly proved the anion exchange mechanism between the N,N’-dialkylbenzimidazolium ionic liquids and Au through single X-ray diffraction.Subsequently,we studied the effects of extending the length of carbon chain or increasing the branched chain on the extraction of gold.It was found that extending the length of carbon chain would increase the extraction efficiency of Au,and the increase of branched chain with keeping a certain carbon number would not influence the extraction efficiency of Au.Theoretical calculations was taken to explain this phenomenon,and we speculated the solubility of extracted complex in water is the main cause,because of rather close charges of benzimidazolium head group C-H of the three ionic liquid extractants studied,whether extending the carbon chain length or increasing the branched chain.It was found that the solubility of ionic liquids in water is greatly reduced after extending the carbon chain length,which increased utilization of ionic liquids. |
