Studies On Syntheses, Properties Of Guanidinium Salts And Applications Of Br(?)nsted Acidic Guanidinium Ionic Liquids

The development of environmentally friendly catalysts,solvents for organic chemistry is one very important area of green chemistry. From both economical and environmental points of view, the use of clean manufacturing processes and technologies is very promising. In the last few years room temperature ionic liquids (RTILs), have been recognized as a possible environmentally benign alternative to chemical volatile solvents. The RTILs show useful properties such as thermal stability, high ionic conductivity, negligible vapor pressure and large electrochemical window.The RTILs emerged as an alternative recyclable environmentally benign reaction media for chemical process including bio and chemical catalysis.The physical and chemical properties of RTILs, often defined as"green solvents and designer solvents",can indeed varied over a wide range by selection of suitable cations and anions.The most common RTILs in use are salts with N-alkylpyridinum and N,N-dialkylimidazolium cations, such as [Bmim][PF6] (1- butyl -3-Methylimidazolium hexafluorophosphate) and [Bmim][BF4] (1- butyl-3-methylimidazolium tetrafluoroborate). At present,in order to substitute toxic,harmful organic solvents and develop highly efficient green chemistry process,to develop synthesis and application of RTIL,especially, as solvents and catalysts have received much attention.There are several advantages and reasons for synthesizing alkylguanidinium-based ionic liquids: 1. The positive charge in the guanidinium salts is delocalized over one carbon and three nitrogen atoms, which gives them a high degree of thermal stability compared to tetraalkylammonium salts.2 The alkyl- guanidinium salts are widely used as phase transfer catalyst due to their exceptional stability at high temperature. 3. Alkylguanidinium salts exhibit some particularities due to its extraordinary bulkiness. For example, the literature reports structural features, which support the existence of an electron-deficient state at the central carbon atom surrounde by the three nitrogen atoms.In this paper, we designed and synthesized a series of guanidinium halides and guanidinium ionic liquids(GRTILs) to study their properties and applications.The main content is outlined as following:(1) Fifteen guanidinium halides and guanidinium ionic liquids were designed and synthesized. We studied in full the physico-chemical properties of a number of GRILs, involving density, viscosity, solubility, polarity, melt point, thermal stability and electrochemical property. The results as following: The density of GRTILs decreases as the bulk of the cation decreased and increases as the bulk of the anion increased. The viscosity of GRTILs decreases as the bulk of the anion and cation decreased. All the GRTILs were miscible in absolute ethanol, and in the case of examples containing less polar anions ([PF6]) were immiscible in water, however, the GRTILs containing anions([BF4],[NO3],[CF3SO3]) were miscible in water. When we study the polarity of the GRTILs with the aid of the fluorescene spectra, we found that the polarity of displaying in the range polarity of the alcohols, moreover, the influence of anions and cations on polarity of the GRTILs were not obvious. All GRTILs are low melting compounds, above their melting points they are stable to at least 300oC. From the datas determined ,we found the GRTILs exhibiting the larger electrochemical window of 3.5V, however, the GRTILs exhibit lower conductivity than imidazolium ionic liquids, most propably due to the larger viscosity of the GRTILs.(2) Novel Br?nsted acidic ILs based on a cyclic guanidinium cation has been synthesized. The IL, as a stong Br?nsted acid catalyst and solvent, shows high catalytic activity and biphsaic behavor in esterification of carboxylic acids and alcohols. The producted esters as a separate phase can be decanted conveniently out from the IL and the IL can be recyclable without any activity loss.