@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:000259381200014, title = {Unusual temperature dependence of salt effects for {\textquoteleft}{\textquoteleft}on water{\textquoteright}{\textquoteright} wittig reaction: hydrophobicity at the interface}, journal = {Chemical Communications}, number = {37}, year = {2008}, month = {MAY}, pages = {4445-4447}, publisher = {ROYAL SOC CHEMISTRY}, type = {Article}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

An unusual variation with temperature of the salt effects in aqueous Wittig reaction is observed, suggesting that hydrophobic acceleration of reactions comprising {\textquoteleft}{\textquoteleft}on water{\textquoteright}{\textquoteright} reactants is fundamentally different from that for reactions with small non-polar solutes.

}, issn = {1359-7345}, doi = {10.1039/b809127g}, author = {Tiwari, Shraeddha and Kumar, Anil} } @article { ISI:000272338600007, title = {Interfacial reactivity of {\textquoteleft}{\textquoteleft}on water{\textquoteright}{\textquoteright} reactions in the presence of alcoholic cosolvents}, journal = {Journal of Physical Chemistry A}, volume = {113}, number = {49}, year = {2009}, month = {DEC}, pages = {13685-13693}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

A detailed study of the variation in the interfacial reactivity and selectivity of {\textquoteleft}{\textquoteleft}on water{\textquoteright}{\textquoteright} reactions in the presence of increasing amounts of alcoholic cosolvents is discussed in the present work. The initial increase in the rates of {\textquoteleft}{\textquoteleft}on water{\textquoteright}{\textquoteright} reactions on the addition of alcoholic cosolvents is contrary to the sharp decrease in rates observed for homogeneous aqueous reactions. The existing theoretical framework is presented in terms of a typical {\textquoteleft}{\textquoteleft}on water{\textquoteright}{\textquoteright} process to enable a discussion of the experimental observations with reference to changing composition of the reaction medium. On the basis of the interesting observations of reactivity and selectivity variations with composition of the reaction medium, a simple {\textquoteleft}{\textquoteleft}signature{\textquoteright}{\textquoteright} characteristic for {\textquoteleft}{\textquoteleft}on water{\textquoteright}{\textquoteright} reactions is proposed.

}, issn = {1089-5639}, doi = {10.1021/jp906281g}, author = {Tiwari, Shraeddha and Kumar, Anil} } @article { ISI:000300462600010, title = {Viscosity dependence of intra- and intermolecular diels-alder reactions}, journal = {Journal of Physical Chemistry A}, volume = {116}, number = {4}, year = {2012}, month = {FEB}, pages = {1191-1198}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The kinetics of the bimolecular Die Is Alder reaction between anthracene-9-carbinol and N-ethyl maleimide have been studied in a series of pyridinium-based ionic liquids with the tetrafluoroborate ([BF4](-)) and the bis(trifluorosulfonimide) ([NTf2](-)) anions and the viscosity dependence of the rate constants have been compared with the results for the intramolecular Diels Alder reaction of (E)-1-phenyl-4-[2-(3-methyl-2-butenyloxy)benzylidene]-5-pyrazolone. The comparison leads to the surprising observation that the intermolecular reaction is less susceptible to viscosity variations of the ionic liquids as compared to the intramolecular reaction. The observed similarities and differences emphasize the complicated nature of solvent friction on the kinetics of cycloaddition reactions. The results are explained by considering the bimolecular and intramolecular processes as cases of translational and rotational diffusion, respectively. Plausible indicators of microviscosity consistent with the kinetic data for the Diels-Alder reactions are briefly discussed along with the constraints involved in designing a general microviscosity scale.

}, issn = {1089-5639}, doi = {10.1021/jp208989z}, author = {Tiwari, Shraeddha and Kumar, Anil} }