@article { ISI:000260923000048, title = {Intramolecular Diels-Alder reaction in ionic liquids: effect of ion-specific solvent friction}, journal = {Journal of Organic Chemistry}, volume = {73}, number = {22}, year = {2008}, month = {NOV}, pages = {9075-9083}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The present work aims at understanding the role of viscosity or solvent friction in ionic liquids for an intramolecular Diels-Alder (IMDA) reaction of (E)-1-phenyl-4-[2-(3-methyl-2-butenyloxy)benzylidene]-5-pyrazolone (1). The results have been analyzed on the basis of the current theoretical models, and their failure to account for the observed trends is discussed in terms of {\textquoteleft}{\textquoteleft}effective{\textquoteright}{\textquoteright} viscosity or microviscosity. The rates of the reaction decrease with the increasing viscosity of the ionic liquids. As evident from the anionic effect, the solute-solvent specific interactions play a role in governing the kinetics of the reaction. The lower viscosities of the bistrifluoromethanesulfonimide [NTf(2)](-) based ionic liquids as compared to those based on tetrafluoroborate [BF(4)](-) anion fail to result in a corresponding acceleration in the rates of the reaction. These contradictory results indicate that solvent microviscosity, rather than the bulk macroscopic viscosity, should be the criteria for selecting the ionic liquids as reaction media.

}, issn = {0022-3263}, doi = {10.1021/jo801802q}, author = {Tiwari, Shraeddha and Khupse, Nageshwar D. and Kumar, Anil} } @article { ISI:000264326100007, title = {Dramatic change in viscosities of pure ionic liquids upon addition of molecular solvents}, journal = {Journal of Solution Chemistry}, volume = {38}, number = {5}, year = {2009}, month = {MAY}, pages = {589-600}, publisher = {SPRINGER/PLENUM PUBLISHERS}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Viscosities of binary mixtures of pyridinium based ionic liquids (1-butyl pyridinium tetrafluoroborate, [BP][BF(4)], 1-butyl 3-methyl pyridinium tetrafluoroborate [3-MBP][BF(4)], 1-butyl 4-methyl pyridinium tetrafluoroborate, [4-MBP][BF(4)]), and phosphonium based ionic liquids, (tetrabutyl phosphonium alaninate, [TBP][Ala]; tetrabutyl phosphonium valinate, [TBP][Val]) with the molecular solvents, water, methanol and dichloromethane, have been measured at 298.15 K. A Brookfield ultra-rheometer was employed to measure the reported viscosities. The drop in viscosity in the close vicinity of pure ionic liquid is more prominent in polar solvents like water compared to less polar solvents. The temperature dependence of this observation was also studied for binary mixtures of [4-MBP][BF(4)] with water in range of 298.15-323.15 K. The Vogel-Fulcher-Tamman (VFT) equation was employed to investigate the temperature dependence of the viscosities of pure pyridinium-based ionic liquids in the temperature range from 298.15-323.15 K.

}, keywords = {ionic liquids, Molecular solvents, VFT equations, viscosity}, issn = {0095-9782}, doi = {10.1007/s10953-009-9390-7}, author = {Khupse, Nageshwar D. and Kumar, Anil} } @article { ISI:000273404500044, title = {Contrasting thermosolvatochromic trends in pyridinium-, pyrrolidinium-, and phosphonium-based ionic liquids}, journal = {Journal of Physical Chemistry B}, volume = {114}, number = {1}, year = {2010}, month = {JAN}, pages = {376-381}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Thermosolvatochromism has been studied in three series of ionic liquids, pyridinium-based 1-butylpyridinium, 1-hexylpyridinium, and 1-octylpyridinium with bis(trifluoromethylsulfonyl)imide [NTf2] and tetrafluoroborate [BF4] anions, pyrrolidinium-based ionic liquids 1-methyl-1-butylpyrrolidium, 1-methyl-1-hexylpyrrolidium, 1-methyl-1-octylpyrrolidium with bis(trifluoromethylsulfonyl) imide anion and phosphonium-based ionic liquids tetrabutylphosphonium with alanate and valinate anions. The effect of increase in alkyl chain length and temperature on normalized polarity E-T(N), Kanilet-Taft parameters, hydrogen bond donor ability (alpha), hydrogen bond acceptor ability (beta), and polarizability (pi*) was investigated in the temperature range of 298-353 K. Interestingly, the polarity decreases with temperature in the case of pyridinium- and pyrrolidinium-based ionic liquids, and it increases with temperature in the case of phosphonium-based ionic liquids.

}, issn = {1520-6106}, doi = {10.1021/jp908498p}, author = {Khupse, Nageshwar D. and Kumar, Anil} } @article { ISI:000279017900002, title = {Ionic liquids: new materials with wide applications}, journal = {Indian Journal of Chemistry Section A-Inorganic Bio-Inorganic Physical Theoretical \& Analytical Chemistry}, volume = {49}, number = {5-6, SI}, year = {2010}, month = {MAY}, pages = {635-648}, publisher = {NATL INST SCIENCE COMMUNICATION-NISCAIR}, address = {DR K S KRISHNAN MARG, PUSA CAMPUS, NEW DELHI 110 012, INDIA}, abstract = {

Ionic liquids have emerged as possible substitutes for volatile organic solvents and have found many applications in a variety of research areas. In this review, an effort has been made to discuss the special properties of ionic liquids that render these unique solvent media useful in chemical transformations, electrochemical applications, extractions, etc.

}, keywords = {Chemical processes, Electrochemical devices, ionic liquids, Physicochemical properties, Solvent properties, viscosity}, issn = {0376-4710}, author = {Khupse, Nageshwar D. and Kumar, Anil} } @article { ISI:000275937400001, title = {Solvent-induced viscosity changes in ionic liquids - a review}, journal = {Proceedings of the National Academy of Sciences India Section A-Physical Sciences}, volume = {80}, number = {1}, year = {2010}, month = {JAN}, pages = {1-12}, publisher = {NATL ACAD SCIENCES INDIA}, address = {5 LAJPATRAI RD, ALLAHABAD 211002, INDIA}, abstract = {

The high viscosity of several ionic liquids is an undesirable property for their applications in a variety of chemical reactions and electrochemical devices. Addition of a solvent in an ionic liquid is known to reduce its high viscosity to a great extent. In this review, an attempt has been made to examine the published data on the reduction in viscosities of many ionic liquids upon the addition of molecular solvents, including water. A tentative description has been provided for the drop in viscosities under these conditions. Analysis of the viscosity data with the help of empirical equations has been summarized. This critical review also outlines the future outlook of the required studies that might be useful to those who are interested in using ionic liquids for a variety of applications.

}, keywords = {ionic liquids, solvent, viscosity}, issn = {0369-8203}, author = {Khupse, Nageshwar D. and Kumar, Anil} } @article { ISI:000279017900010, title = {Temperature dependent viscosity of mixtures of ionic liquids at different compositions}, journal = {Indian Journal of Chemistry Section A-Inorganic Bio-Inorganic Physical Theoretical \& Analytical Chemistry}, volume = {49}, number = {5-6, SI}, year = {2010}, month = {MAY}, pages = {727-730}, publisher = {NATL INST SCIENCE COMMUNICATION-NISCAIR}, address = {DR K S KRISHNAN MARG, PUSA CAMPUS, NEW DELHI 110 012, INDIA}, abstract = {

This work presents experimental investigations of viscosities of the mixtures of ionic liquids, viz., [bmim][BF(4)] + [bmim][PF(6)] and [hmim][BF(4)] + [hmim][PF(6)] at different temperatures. The temperature dependence of viscosities of these mixtures has been analysed in the light of Vogel-Fulcher-Tammann (VFT) equation with excellent accuracy. The viscosities of the mixtures have been analysed using a simple mixing rule.

}, keywords = {ionic liquids, viscosity}, issn = {0376-4710}, author = {Khupse, Nageshwar D. and Kurolikar, Shabana R. and Kumar, Anil} } @article { ISI:000294701300010, title = {Cosolvent-directed diels-alder reaction in ionic liquids}, journal = {Journal of Physical Chemistry A}, volume = {115}, number = {36}, year = {2011}, month = {SEP}, pages = {10211-10217}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The rate constants of a bimolecular Diels-Alder reaction in binary mixtures of ionic liquids prepared in molecular solvents were analyzed to investigate the effect of viscosity of the medium and solvent effect. In this connection, we have carried out the Diels-Alder reaction of anthracene 9-carbinol with N-ethyl maleimide in binary mixtures of pyridinium-based ionic liquids, 1-butyl-pyridinium tetrafluoroborate, 1-buty1-3-pyridinium tetrafluoroborate, and 1-butyl-4-methyl pyridinium tetrafluoroborate in water, methanol, and chloroform at 298.15 K. The rates of reaction decreased, caused by gradually increasing the volume fraction of ionic liquids in solvents for all three ionic liquids. The kinetic results demonstrate a successful application of the pairwise interaction model built upon the concept of enforced hydrophobic hydration. A temperature-dependent study of kinetics of the Diels-Alder reaction was carried out in the binary mixtures of ionic liquids in water and was explained by the entropy-enthalpy compensation effect based upon activation parameters. Kinetics of the Diels-Alder reaction in highly aqueous medium was noted to be entropically driven.

}, issn = {1089-5639}, doi = {10.1021/jp205181e}, author = {Khupse, Nageshwar D. and Kumar, Anil} } @article { ISI:000286639500014, title = {Delineating solute-solvent interactions in binary mixtures of ionic liquids in molecular solvents and preferential solvation approach}, journal = {Journal of Physical Chemistry B}, volume = {115}, number = {4}, year = {2011}, month = {FEB}, pages = {711-718}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The effect of solute-solvent and solvent-solvent interactions on the preferential solvation of solvatochromic indicators in binary mixtures of ionic liquids with molecular solvents has been investigated. The binary mixtures of the pyridinium-based ionic liquids 1-butylpyridinium tetrafluoroborate ([BP][BF4]), 1-butyl-3-methylpyridinium tetrafluoroborate ([3-MBP][BF4]), and 1-butyl-4-methylpyridinium tetrafluoroborate ([4-MBP][BF4]) with molecular solvents like water, methanol, and dichloromethane have been selected for this investigation. The effect of addition of ionic liquids to molecular solvents on the polarity parameters E-T(N), Kamlet-Taft parameters, hydrogen bond donor ability (HBD) (alpha), hydrogen bond acceptor ability (HBA) (beta), and polarizability (pi*) was obtained. The polarity parameters of the mixture display nonideality on addition of ionic liquids to water and dichloromethane. On the other hand, strong synergetic effects were seen in the ionic liquid-methanol binary mixtures. The preferential solvation models have been employed to analyze the collected data in order to achieve information on solute-solvent interactions in these binary mixtures.

}, issn = {1520-6106}, doi = {10.1021/jp110040a}, author = {Khupse, Nageshwar D. and Kumar, Anil} } @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:000346235600051, title = {Solvent-mediated molar conductivity of protic ionic liquids}, journal = {Physical Chemistry Chemical Physics}, volume = {17}, number = {1}, year = {2015}, month = {NOV}, pages = {475-482}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

The molar conductivity, A(m), of protic ionic liquids (PILs) in molecular solvents is measured at 298.15 K. The decrease in the A(m) values of PILs is observed with an increase in the concentration of PILs. The limiting molar conductivities, A(m)(0), were obtained for each PIL in different molecular solvents using a least squares method. The A(m)(0) data for PILs were correlated with the structural aspects of PILs and solvent properties. The polar protic solvents show poor ionic association as compared to the polar aprotic solvents, which is discussed on the basis of the hydrogen bond donating (HBD) ability of solvents and PILs. The alkyl chain substitution of anions plays a significant role in the ionic association of the PILs. The diffusion coefficient D-0 and the transport number t were determined, which were consistent with the A(m)(0) values of PILs in water. The A(m)(0) and D-0 values are dependent on the hydrodynamic radius of anions of these ionic liquids. The extent of ionic association for each PIL was discussed using temperature dependent A(m) data for aqueous PIL systems in terms of the Walden plot.

}, issn = {1463-9076}, doi = {10.1039/c4cp04591b}, author = {Thawarkar, Sachin and Khupse, Nageshwar D. and Kumar, Anil} } @article { ISI:000373738200010, title = {Comparative investigation of the ionicity of aprotic and protic ionic liquids in molecular solvents by using conductometry and NMR spectroscopy}, journal = {Chemphyschem}, volume = {17}, number = {7}, year = {2016}, month = {APR}, pages = {1006-1017}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {

Electrical conductivity (sigma), viscosity (), and self-diffusion coefficient (D) measurements of binary mixtures of aprotic and protic imidazolium-based ionic liquids with water, dimethyl sulfoxide, and ethylene glycol were measured from 293.15 to 323.15K. The temperature dependence study reveals typical Arrhenius behavior. The ionicities of aprotic ionic liquids were observed to be higher than those of protic ionic liquids in these solvents. The aprotic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate, [bmIm][BF4], displays 100\% ionicity in both water and ethylene glycol. The protic ionic liquids in both water and ethylene glycol are classed as good ionic candidates, whereas in DMSO they are classed as having a poor ionic nature. The solvation dynamics of the ionic species of the ionic liquids are illustrated on the basis of the (HNMR)-H-1 chemical shifts of the ionic liquids. The self-diffusion coefficients D of the cation and anion of [HmIm][CH3COO] in D2O and in [D-6]DMSO are determined by using H-1 nuclei with pulsed field gradient spin-echo NMR spectroscopy.

}, keywords = {conducting materials, Electrochemistry, electrostatic interactions, Ion pairs, ionic liquids}, issn = {1439-4235}, doi = {10.1002/cphc.201501156}, author = {Thawarkar, Sachin and Khupse, Nageshwar D. and Kumar, Anil} } @article {43571, title = {ESP promoted "on water" click reaction: a highly economic and sustainable protocol for 1,4-disubstituted-1H-1,2,3-triazole synthesis at room temperature}, journal = {Chemistryselect}, volume = {1}, year = {2016}, month = {NOV}, pages = {6016-6019}, abstract = {A highly economic and green protocol for azide-alkyne cyclo-addition reactions in water has been developed which offers a mild, practical and inexpensive basic alternative to the conventional protocols. The protocol uses readily available, considered as waste material, Egg Shell Powder (ESP) as an additive for CuAAC reaction. The reactions proceeded in water in presence of this basic waste material derived additive under {\textquoteright}external base/ligand/reducing agent/organic solvent{\textquoteright} free conditions affording good to excellent yields of the desired products.}, doi = {10.1002/slct.201601267}, author = {Konwar, Manashjyoti and Ali, Abdul A. and Chetia, Mitali and Saikia, Prakash J. and Khupse, Nageshwar D. and Sarma, Diganta} } @article {43805, title = {Kinetic profile and catalytic activity of transition metal-based ionic liquids for reduction of nitroarenes via in situ formation of nanoparticles}, journal = {Chemistryselect}, volume = {2}, year = {2017}, month = {AUG}, pages = {6833-6843}, type = {Article}, abstract = {

The experimentally determined apparent rate constant (k(app)) shows that the [BmIm](2)[PdCl4] and [BmIm](2)[NiCl4] act as effective catalysts for the reduction of nitroarenes to aminoarenes in the presence of NaBH4. The TEM, XPS, XRD and dynamic light scattering studies show that there is in situ formation of Pd and Ni metal Nanoparticles (NPs) from the reduction of [BmIm](2)[PdCl4] and [BmIm](2)[NiCl4], respectively which are responsible for the enhancement in the catalytic activity. Thus, in the presence of the ionic liquid stabilized metal NPs show higher catalytic activity in comparison to the NPs stabilized with other capping agents as reported. The order of k(app) as 1) PNP \> 2-BrPNP \> 2-APNP and 2) PNP \> ONP \> 2-NR for reduction of nitroarenes using [BmIm](2)[PdCl4] and [BmIm](2)[NiCl4] and its correlation explained on the basis of electronic structure and hydrogen bonding ability of nitroarenes. The thermodynamic parameters such as E-a, Delta H-$\#$, Delta S-$\#$ and Delta G($\#$) are in agreement with the surface catalyzed reduction reaction of PNP in the presence of NPs as catalyst. The kapp values illustrated the reduction reaction follow the LangmuirHinshelwood (L-H) mechanism.

}, doi = {10.1002/slct.201701601}, author = {Thawarkar, Sachin R. and Khupse, Nageshwar D. and Kumar, Anil} } @article {44131, title = { Plasmonic behavior of ionic liquid stabilized gold nanoparticles in molecular solvents}, journal = {New Journal of Chemistry}, volume = {41}, year = {2017}, month = {NOV}, pages = {12989-12995}, type = {Article}, abstract = {In this paper, we have demonstrated the facile synthesis of stable gold nanoparticles (AuNPs) using imidazolium ionic liquids (ImILs) as a stabilizer as well as a surfactant and their surface plasmon resonance (SPR) in different molecular solvents with varying dielectric properties. The preparation of AuNPs capped with N,N{\textquoteright}-dialkyl ImILs of different chain lengths (denoted as [C-4, C-n-im]Br, n = carbon number of the alkyl chain) has been investigated. With one long alkyl chain (n >= 14), these AuNPs could be stably dispersed in solution over a month. The amphiphilic nature of the imidazolium salt dictates the stability and dispersion of these AuNPs in organic or aqueous solvents. Alkyl chain lengths (n >= 14) and the amount of ImILs have insignificant effect on the size of AuNPs and they possess an average size of 5 nm. These ionic liquid stabilized AuNPs were exploited to examine their optical properties when exposed to various solvent systems by measuring the change in the SPR spectrum. It was seen that the position of the SPR band of AuNPs is greatly influenced by the solvents under consideration. The shift in the SPR absorption band is observed to be in the range of 520 nm to 605 nm for AuNP@[C-4,C-16-im]Br from nonpolar to highly polar solvents. The considerable discovery presented here is that the lambda(SPR) of the SPR shifts to the blue with the increase of carbon atom in the alcohol chain from methanol to 1-decanol. Also for polyethylene glycols (PEGs), the lambda(SPR) shifts to the blue with the increase in molecular weight from PEG 200 to PEG 600. In above both cases, the variation in SPR of AuNPs is observed according to the dielectric properties of the medium in addition to the steric factor of alcohols and PEGs during their interaction with AuNP surfaces.}, doi = {10.1039/c7nj01324h}, author = {Thawarkar, Sachin and Thombare, Balu and Khupse, Nageshwar D.} } @article {46954, title = {Binary mixtures of aprotic and protic ionic liquids demonstrate synergistic polarity effect: an unusual observation}, journal = {Journal of Solution Chemistry}, volume = {49}, year = {2020}, month = {FEB}, pages = {210-221}, type = {Article}, abstract = {

In this communication, we demonstrate the solute-solvent and solvent-solvent interactions in the binary mixtures of two aprotic ionic liquids, namely 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, with the protic ionic liquid 1-methylimidazolium acetate. The synergistic effects as expressed by the solvatochromic parameter are noted. This observation is in contrast to the mixing of protic ionic liquids 1-methylpyrrolidium acetate and 4-methylmorpholine acetate with 1-methylimidazolium acetate, respectively. It appears that the synergistic effects in the binary mixtures of aprotic and protic ionic liquids are caused by the formation of hydrogen bonds, since cations are dominant H-bond donors while anions are dominant H-bond acceptors. Preferential solvation models are used to describe the solute-solvent interactions in the binary ionic liquid mixtures.

}, keywords = {binary mixture, Ionic liquid, polarity, Preferential solvation, synergetic effect}, issn = {0095-9782}, doi = {10.1007/s10953-020-00952-w, Early Access Date = FEB 2020}, author = {Thawarkar, Sachin and Khupse, Nageshwar D. and Kumar, Anil} }