离子液体1-丁基-2,3-二甲基咪唑六氟磷酸盐对γ射线辐射稳定性研究

研究了憎水性离子液体1-丁基-2,3-二甲基咪唑六氟磷酸盐(BuMeMeIm]PF6),在氮气保护下,60Coγ射线照射,最大剂量为400 kGy的辐射稳定性。随着辐照剂量的增加,BuMeMeIm]PF6的颜色逐渐加深,紫外-可见光谱(UV-Vis)中吸光度随辐照剂量的增加呈线性增长,但颜色及吸光度的变化均小于1-丁基-3-甲基咪唑六氟磷酸盐(BuMeIm]PF6)。辐照400 kGy后,BuMeMeIm]PF6的傅利叶红外光谱(FTIR)和核磁共振氢谱(1H NMR)谱图均未出现变化。高效液相色谱法(HPLC)分析表明辐照400 kGy后,发生辐解的BuMeMeIm]+的比例约为0.73%,小于同样条件下发生辐解的BuMeIm]+。电喷雾质谱(ESIMS)结果显示BuMeMeIm]+中N-butyl键的断裂可能是阳离子分解的重要原因之一。因此,咪唑环C(2)-H被甲基取代,将会增加咪唑阳离子的辐射稳定性,减小阳离子的辐射分解,使得BuMeMeIm]PF6具有更高的辐射稳定性。

Radiation Stability of Ionic Liquid 1-butyl 2,3-dimethyl Hexafluorophosphate under Gamma Irradiation

The stability of hydrophobic ionic liquid 1-butyl 2,3-dimethylimidazolium hexafluorophosphate(BuMeMeIm]PF 6) was studied by 60 Co gamma-ray irradiation in nitrogen atmosphere for the maximum dose of 400 kGy.BuMeMeIm]PF 6 becomes gradually considerably darkened with increasing gamma-ray irradiation dose.The light absorbance of ionic liquids increases linearly with the irradiation dose.But the change in color and UV-Vis absorbance of BuMeMeIm]PF 6 was obviously less than that of 1-butyl-3-methylimidazolium hexafluorophosphate( BuMeIm]PF 6).Both the FTIR and 1 H NMR spectra of BuMeMeIm]PF 6 show no difference before and after irradiation.HPLC analysis proved that the radiolysis ratio of the BuMeMeIm]PF 6 is less than that of BuMeIm]PF 6.ESIMS data indicate that the loss of the Bu· group from the imidazolium ring is one of the initial step of BuMeMeIm] + cation radiolysis.Therefore,the substitution of H at C2 position on the imidazolium ring with methyl group increases the radiochemical stability of the imidazolium cation.