Counterintuitive solvation effect of ionic-liquid/DMSO solvents on acidic C–H dissociation and insight into respective solvation. Issue 12 (10th March 2020)

• Record Type: Journal Article
• Authors: Luo, Wenzhi; Mao, Chong; Ji, Pengju; Wu, Jun-Yan; Yang, Jin-Dong; Cheng, Jin-Pei
• Is Part Of: Chemical science. Volume 11:Issue 12(2020)
• Page Start: 3365
• Page End: 3370
• Publication Date: 2020-03-10
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c9sc06341b
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : The dependence of PhCH(CN)2 p K a on the molar fraction of ionic liquids in ionic–molecular binary mixtures showed a nonlinear three-fragment plot, which was rationalized for the first time by the respective roles of each solvent component for solvation. Abstract : How would acidic bond dissociation be affected by adding a small quantity of a weakly polar ionic liquid IL (the "apparent" or "measured" dielectric constant ε of the IL is around 10–15) into a strongly polar molecular solvent ( e.g., ε of DMSO: 46.5), or vice versa ? The answer is blurred, because no previous investigation was reported in this regard. Toward this, we, taking various IL/DMSO mixtures as representatives, have thoroughly investigated the effects of the respective solvent in ionic–molecular binary systems on self-dissociation of C–H acid phenylmalononitrile PhCH(CN)2 via p K a determination. As disclosed, in this category of binary media, (1) no linear correspondence exists between p K a and molar fractions of the respective solvent components; (2) only ∼1–2 mol% of weakly polar ILs in strongly polar DMSO make C–H bonds even more dissociative than in neat DMSO; (3) a small fraction of DMSO in ILs (<10 mol%) can dramatically ease acidic C–H-dissociation; and (4) while the DMSO fraction further increases, its acidifying effect becomes much attenuated. These findings, though maybe counterintuitive, have been rationalized on the basis of the precise p K a measurement of this work in relation to the respective roles of each solvent component in solvation.