Effects of Alkyl Chain Length and Solvents on Thermodynamic Dissociation Constants of the Ionic Liquids with One Carboxyl Group in the Alkyl Chain of Imidazolium Cations

Abstract

Thermodynamic dissociation constants of the Brønsted acidic ionic liquids (ILs) are important for their catalytic and separation applications. In this work, a series of imidazolium bromides with one carboxylic acid substitute group in their alkyl chain ([{(CH2)nCOOH}mim]Br, n = 1,3,5,7) have been synthesized, and their dissociation constants (pKa) at different ionic strengths have been determined in aqueous and aqueous organic solvents at 0.1 mole fraction (x) of ethanol, glycol, iso-propanol, and dimethyl sulfoxide by potentiometric titrations at 298.2 K. The standard thermodynamic dissociation constants (pKa(T)) of the ILs in these solvents were calculated from the extended Debye-Hückel equation. It was found that the pKa values increased with the increase of ionic strength of the media and of the addition of organic solvent in water. The pKa(T) values also increased with the increase of the alkyl chain length of cations of the ILs. In addition, the effect of solvent nature on pKa(T) values is interpreted from solvation of the dissociation components and their Gibbs energy of transfer from water to aqueous organic solutions.

Structures and Synthesis of Zwitterionic Polymers

“…This is due to the strong electron withdrawing effect of the ammonium group, which levels off for x  4, resulting in pK a values of about 4.5. The acidity of carboxyl groups is also increased by attachment to aromatic cations, with comparable distance effects, as reported for imidazoliocarboxylates [74]. The same effect also decreases the pK a value of pyridiniocarboxylates XI to 1.8 [75].…”

Sulfobetaines Meet Carboxybetaines: Modulation of Thermo- and Ion-Responsivity, Water Structure, Mechanical Properties, and Cell Adhesion

“…The different chemical reactivity of carboxylate based on the length of a linker between the charged moieties was used for the preparation of chemically gradient hydrogel . However, in the present case, the vicinity of a sulfobetaine segment can act as a highly ionic environment and could lead to increasing of the p K a to higher value as was observed for carboxybetaine-based ionic liquid . It is important to note that this approach allows for the introduction of functional molecules, tuning and modulating optical and solution properties while retaining the zwitterionic character of the main polymeric backbone.…”

“…58 However, in the present case, the vicinity of a sulfobetaine segment can act as a highly ionic environment and could lead to increasing of the pK a to higher value as was observed for carboxybetaine-based ionic liquid. 59 It is important to note that this approach allows for the introduction of functional molecules, tuning and modulating optical and solution properties while retaining the zwitterionic character of the main polymeric backbone. This approach also allows the UCST response to be tailored not only by a segment but also by a (bio)component covalently bound to a polymeric backbone in post polymerization step, which is the subject of our ongoing research.…”

Physicochemical Properties of Various 2-Hydroxyethylammonium Sulfonate -Based Protic Ionic Liquids and Their Potential Application in Hydrodeoxygenation

“…The standard method of determining the p K a of substance was described in the literature (Chen et al, 2014). The p K a values of various PILs were obtained by acid–base titration.…”