Trimethylpyrazolium Ionic Liquids Lab Report

1-Aryl-2,3,5-trimethylpyrazolium ionic liquids

Melek Canbulat Özdemir1 and Beytiye Özgün*

Department of Chemistry, Faculty of Science, Gazi University, 06500 Teknikokullar,
Ankara, Turkey

Abstract
A series of new 1-aryl-2,3,5-trimethylpyrazolium ionic liquids were synthesized and characterized. The influence of electron-withdrawing and -donating substituent at the para-position of the phenyl ring (-NO2, -Cl, -Br, -H, -Me, -OMe) on the properties of synthesized salts were investigated by keeping alkyl part constant (methyl) for anions CH3SO3-, BF4- and PF6-. Thermal properties (melting points, thermal stabilities) and electrochemical stabilities (EW) of all salts were investigated. In addition, thermophysical properties ( density, viscosity and refractive index) of liquid salts at room temperature ( 2a,2b, 2d, 2e) were measured as a function of temperature. The results indicated that ordinarily electron-withdrawing substituents increases melting points of pyrazolium salts while –donating substituents decreases their melting points. The salts have thermal stability in the range of 247.5- 387.5 ºC and exhibit a large electrochemical window of 4.39 V.

Keywords: Ionic liquids; 3,5-Dimethylpyrazole; Methanesulfonate;

As seen in Figure 1 and Table 1 electron withdrawing substituents lead to higher melting points while electron donating substituents lead to lower melting points. The influence of the counterion can be easily seen by comparing the pyrazolium salts which have same cation (Figure 1, Table1). It is remarkable that most of the methanesulfonate salts (except 2c and 2f) are in a liquid state at room temperature while all hexafluorophosphate and tetrafluoroborate (except 3e) are in solid state at room