Study On Transient Reaction Kinetics Of Imidazolium And Quaternary Ammonium Ionic Liquids

Room temperature ionic liquids which have been studied frantically in recent years have applicattion in a lot of domains, such as organic synthesis, electrochemistry, extraction (fractionation) and so on. But many reaction mechanisms in ionic liquids need to be explored indeed. Reaction mechanisms can be studied via pulse radiolysis and laser flash photolysis which is a good way. In this paper, we studied the transient reaction mechanisms of imidazolium cations of different substituted groups on the ring with hydrated electrons (eaq–), hydroxyl radicals (●^OH) and sulfate anion radical (SO₄^{●–_</sup>; and solvated electrons in mixed solutions containing ionic liquids and ethanol; and also xanthone in in mixed solutions containing ionic liquids and acetonitrile.We examined the reaction rate constants of different imidazolium-based cations with hydrated electrons, hydroxide radicals and sulfate anion radicals. Changing the length on the imidazole ring and anion types of substituting groups showed no influence to the rate constants with hydroxide radicals and sulfate anion radicals. The reaction rate constants of imidazolium-based cations with hydrated electrons are classified into two groups, one using imidazolium ionic liquid with the C2-alkylation of imidazole ring and the other no alkylation of the position 2' on the imidazole ring. It is found that the imidazolium ionic liquids which are hydroxylated at the position 2' on the imidazole ring can repress the reaction reactivity with hydrated electrons.Pulse radiolysis experiments were conducted on the probe molecule, pyrene, in mixed solutions containing ethanol and ammonium ionic liquid with different volume. The formation of pyrene radical anion (Py·- was observed at 490nm and the rate constants of the Py?- formation were about (1.2±0.2)×1010L·mol-1·s-1. Moreover,the rate constants are changed greatly with increasing of the ILs concentration in the mixture solutions. The results can be assumed that the dry electrons produce in very short time scales after electron pulse and the solvated electrons can react with pyrene to generate its radical anion in nanosecond time scale.The transient absorption spectra and energy transfer process of xanthone (XAN) in the binary mixtures of [bmim][PF6] and acetonitrile (MeCN) have been investigated by laser photolysis at an excitation wavelength of 355 nm. A spectral blue shift of 3XAN* was observed in the neat ILs or IL/MeCN mixtures compared to MeCN. Moreover, with increasing VIL, the rate constants of energy transfer decreased rapidly.The results of the paper can provide more for the research in neat ionic liquids in the radiation chemistry field, including the rate constants of redox reactions in neat ionic liquids.}