Aqueous N-H acid bis(trifluoromethylsulfonyl) imide Solution - [C4mim][Tf2N] Ionic Liquid Biphasic System: an Original Investigation by Diffusion Ordered Spectroscopy Nuclear Magnetic Resonance

Abstract

Transfers of solutes from an aqueous solution to an ionic liquid and vice versa has been well studied for years. On the other hand, influence of transferred solutes on the ionic liquid's network is not yet evaluated. Therefore, we focus on the aqueous - ionic liquid biphasic system composed of two immiscible solutions containing N-H acid bis(trifluoromethylsulfonyl) imide and [C4mim][Tf2N] ionic liquid. After mixing and separation of the two phases, a part of water, H3O+, [Tf2N−] and H[Tf2N] anions are transferred into [C4mim][Tf2N] ionic liquid because H[Tf2N] has a salting in effect. The presence of this solutes might modify the local structure of [C4mim][Tf2N] ionic liquid. So far, our goal is to evaluate this structural change using several tools. For this, one dimensional 1H, 19F and Diffusion Ordered Spectroscopy Nuclear Magnetic Resonance were carried out on [C4mim][Tf2N] ionic liquid. We observed that some of water molecules are free and formed local microstructure as water pocket inside the ionic liquid network. The others are hydrogen bonded to [Tf2N−] anions as Tf2N−….H-O-D….Tf2N− for example. As long as the mole fraction of water in the ionic liquid remains less than or equal to that of [C4mim+] or [Tf2N−] the structure of the network is maintained. Free water moves at its own speed and bound water is an inclusion in the [C4mim][Tf2N] network. As soon as the mole fraction of the water is greater than that of [C4mim+] or [Tf2N−], the network of [C4mim][Tf2N] ionic liquid is gradually dislocated. Charged clusters composed with [C4mim+], [Tf2N−] and bond water are build and free water flow between them.