@article { ISI:000299742000025, title = {Do anions influence the polarity of protic ionic liquids?}, journal = {Physical Chemistry Chemical Physics}, volume = {14}, number = {8}, year = {2012}, month = {DEC}, pages = {2754-2761}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Polarity studies in two classes of imidazolium-based protic ionic liquids (PILs) possessing [HSO4](-), [HCOO](-),[CH3COO](-) and [CH3CH2COO](-) anions were carried out using a solvatochromic method from 298.15 to 353.15 K. For 1-methylimidazolium class of PILs, ET(30) was found to be independent over the entire range of temperature, while ET(30) was noted to decrease with a rise in temperature in the case of 1-butylimidazolium class of PILs containing [CH3COO](-) and [CH3CH2COO](-) anions. The ET(30) value decreases in both the classes upon varying the anions ([HSO4](-), [HCOO](-), [CH3COO](-) and [CH3CH2COO](-)). The E-T(30) value is controlled by hydrogen bond acceptor basicity, b, and dipolarity/polarizability, pi*. The E-T(30) value for PILs varies inversely to the strength of the coulombic interaction between ions in PILs. Strong interactions between ions lead to lower E-T(30) values. Unlike the poor thermal effect on E-T(30), the Kamlet-Taft parameters i.e. alpha, beta and pi* have pronounced thermal effect in the imidazolium-based PILs. Variation in the Kamlet-Taft parameters is controlled by the stabilization of ions and the degree of proton transfer from Bronsted acid to Bronsted base.

}, issn = {1463-9076}, doi = {10.1039/c2cp23256a}, author = {Shukla, Shashi Kant and Khupse, Nageshwar D. and Kumar, Anil} } @article { ISI:000317349300004, title = {Do protic ionic liquids and water display analogous behavior in terms of hammett acidity function?}, journal = {Chemical Physics Letters}, volume = {566}, year = {2013}, month = {APR}, pages = {12-16}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

We address an issue whether the strength of carboxylic acids in water is linear with respect to that in ionic liquids. Strength of carboxylic acids in water and different PILs using Hammett function (Ho) has revealed interesting linear correlation between the Ho function for all acids in PILs and PIL-water in spite of large structural and electronic differences. These observations suggest that different structural and electronic features of PILs and water behave analogously towards Ho. This linearity in Ho functions between PILs and PIL-water systems can be used to develop predictive method to calculate Ho values. (c) 2013 Elsevier B.V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2013.02.029}, author = {Shukla, Shashi Kant and Kumar, Anil} } @article { ISI:000353931000022, title = {Dissociation of equimolar mixtures of aqueous carboxylic acids in ionic liquids: role of specific interactions}, journal = {Journal of Physical Chemistry B}, volume = {119}, number = {17}, year = {2015}, month = {APR}, pages = {5537-5545}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Hammett acidity function observes the effect of protonation/deprotonation on the optical density/absorbance of spectrophotometric indicator. In this work, the Hammett acidity, H-0, of equirriolar mixtures of aqueous HCOQH, CH3COOH, and CH3CH2COOH was measured in 1-methylimidazolium-, 1-methylpyrrolidinium-, and 1-methylpiperidinium-based protic ionic liquids (PILs) and 1-buty1-3-methylimidazolium-based aprotic ionic liquid (AIL), with formate (HCOO-) anion. Higher H-0 values were observed for the equimolar mixtures of aqueous carboxylic acids in protic ionic liquids compared with those of the aprotic ionic liquid because of the involvement of the stronger specific interactions between the conjugate acid of ionic liquid and conjugate base of carboxylic acids as suggested by the hard soft acid base (HSAB) theory. The different Ho values for the equimolar mixtures of aqueous carboxylic acids in protic and aprotic ionic liquids were noted to depend on the activation energy of proton transfer (E-a,H(+)). The higher activation energy of proton transfer was obtained in AIL indicating lower ability to form specific interactions with solute than that of PILs. Thermodynamic parameters determined by the {\textquoteleft}{\textquoteleft}indicator overlapping method{\textquoteright}{\textquoteright} further confirmed the involvement of the secondary interactions in the dissociation of carboxylic acids. On the basis of the thermodynamic parameter values, the potential of different ionic liquids in the dissociation of carboxylic acids was observed to depend on the hydrogen bond donor acidity (alpha) and hydrogen bond acceptor basicity (beta), characteristics of specific interactions.

}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.5b00056}, author = {Shukla, Shashi Kant and Kumar, Anil} }