2.2 Synthesis of SNDESs and Characterization
The [N2222][CH(CN)2] and [N1111][CH(CN)2] were synthesised by a two-step method. Initially, a 25 wt% methanolic solution of malononitrile (1.5 equiv) was gradually added to a 25 wt % methanolic solution of [N2222][OH] (1 equiv) under ice bath conditions and stirred for 1 h. The temperature was then raised to 323.2 K and stirring continued for an additional 8 hours. The orange-red liquid was obtained by spin evaporation at 323.2 K for 0.5 h, and the orange-red liquid along with excess ether was placed in a separatory funnel. The lower liquid layer was extracted by spin evaporation to yield a reddish-brown liquid, which was characterized by NMR and FT-IR to confirm the formation of the desired product, [N2222][CH(CN)2]. The preparation of [N1111][CH(CN)2] was carried out as above.
Five DESs, including [N2222][CH(CN)2]-EG (1:1), [N2222][CH(CN)2]-Im (1:1), [N2222][CH(CN)2] -SUL (1:1), [N2222][CH(CN)2]-DMEE (1:1) and [N2222][CH(CN)2]-Eim (1:1). [N2222][CH(CN)2] was mixed with each of the five HBDs at a molar ratio of 1:1 at 323.2 K until homogeneous liquids were obtained. The viscosities of five DESs based on [N2222][CH(CN)2] were measured on a Brookfield LVDV-II + Pro viscometer from 303.2~333.2 K with a relative deviation of 1%.