Synthesis, Structure And Property Studies Of N-alkyl Pyridine Ionic Liquids

Ionic liquids (ILs) are known as salts that exist in liquid state below373K in contrast to high temperature molten salts. The salts are currently widely used in fields of organic synthesis, liquid-liquid separations, purification, organic catalysis, polymer materials, and electrochemistry and so on, because of their unique properties such as nonvolatility, almost no measurable vapor pressure, nonflammability and a wide liquid-state temperature range. Much scientific interest is currently focus on the ILs. It is important to grasp the structure-property relationships for assessing the suitability of the salts for specific applications. However, our understanding toward their fundamental nature is still far from complete.In this work, straight bromoalkanes and branched bromoalkanes were as alkylating agent, and KPF6was as the salt with goal anion, the N-alkyl pyridine ionic liquids of [n-C4pyr][PF6],[n-C8pyr][PF6],[n-C12pyr][PF6],[i-C4pyr][PF6] and [t-C4pyr][PF6] were synthesized using two-step method. Meanwhile, by the experimental research, it indicated that reaction temperature and reaction time have great influence on the alkylation and change-anion reaction.The structures of N-alkyl pyridine ionic liquids were studied by respectively the single crystal X-ray diffraction technique, Fourier infrared spectroscopyic and Nuclear magnetic resonance spectrometer. The single crystal X-ray diffraction was used in analysis of the crystal structure of [n-C4pyr][PF6] and[i-C4pyr][PF6]. The data analysis indicated that [n-C4pyr][PF6] crystallizes in the monoclinic system, space group P2(1)/n, with unit-cell parameters a=2.619(3)nm, b=0.6766(7)nm, c=0.7160(7)nm, β=90°,and Z=4. The data analysis indicated that [/-C4pyr][PF6] crystallizes in the monoclinic system, space group P2(1)/c, with unit-cell parameters a=1.05783(19)nm, b=0.97334(18)nm, c=1.3332(3)nm, p=113.032(3)°, and Z=4.Physicochemical properties of N-alkyl pyridine ionic liquids were determined and studied by differentials scanning calorimetry (DSC), thermal gravimetric analysis (TGA). Moreover, the structure-property relationships of N-alkyl pyridine ionic liquids were further analyzed. With the increase of carbon number of alkyl chain, the melting point of ionic liquid decreased at first, and increased after the number of the number of alkyl carbon atoms was above10. If more branched chains were connected with N atom of the pyridine ring, ionic liquid had a higher melting point. The results indicated that the polarities of most N-alkyl pyridine ionic liquids were close to acetone or methanol, and the structure of branched chains had important influence on properties of N-alkyl pyridine ionic liquids.Based on the structure and properties of N-alkyl pyridine ionic liquids, some ionic liquids used as modifiers were respectively introduced into the polymerization system of styrene, the polymer microspheres were prepared by the method of suspension polymerization. The effects of the concentration of the modifier [n-C12pyr][PF6] on the polymerization rate as well as the diameter of latex particles was investigated. According the results of the analysis, the suspension polymerization of styrene was realized when [n-C12pyr][PF6] ionic liquid of certain concentration was used as modifier. Meanwhile, the results also give us the information that the average diameter of the latex particles is about445μm and it becomes smaller when the concentration of modifier increase. The polymerization rate was found to increase with the increase of concentration of modifier. For comparison,[n-C4pyr][PF6] and [n-C8pyr][PF6] were also used as modifier. From the results, it was found that the smallest latex particles, the fastest polymerization rate and most stable emulsion was prepared when [n-C12pyr][PF6] was used comparing with [n-C4pyr][PF6] and [n-C8pyr][PF6] ionic liquid.