Effectsof Alkyl Chain Length and Solvents on ThermodynamicDissociation Constants of the Ionic Liquids with One Carboxyl Groupin the Alkyl Chain of Imidazolium Cations.

Thermodynamicdissociation constants of the Brønsted acidicionic liquids (ILs) are important for their catalytic and separationapplications. In this work, a series of imidazolium bromides withone 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 havebeen determined in aqueous and aqueous organic solvents at 0.1 molefraction (x) of ethanol, glycol, iso-propanol, anddimethyl sulfoxide by potentiometric titrations at 298.2 K. The standardthermodynamic dissociation constants (pKaT) of the ILs in these solvents were calculated from theextended Debye–Hückel equation. It was found that thepKavalues increased with the increaseof ionic strength of the media and of the addition of organic solventin water. The pKaTvalues alsoincreased with the increase of the alkyl chain length of cations ofthe ILs. In addition, the effect of solvent nature on pKaTvalues is interpreted from solvation ofthe dissociation components and their Gibbs energy of transfer fromwater to aqueous organic solutions. [ABSTRACT FROM AUTHOR]