01747nas a2200169 4500008004100000022001400041245009800055210006900153260007100222300001400293490000700307520107100314100002201385700002601407700001601433856012801449 2008 eng d a0022-326300aIntramolecular Diels-Alder reaction in ionic liquids: effect of ion-specific solvent friction0 aIntramolecular DielsAlder reaction in ionic liquids effect of io a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcNOV a9075-90830 v733 a

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 ``effective'' 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.

1 aTiwari, Shraeddha1 aKhupse, Nageshwar, D.1 aKumar, Anil uhttps://library.ncl.res.in/content/intramolecular-diels-alder-reaction-ionic-liquids-effect-ion-specific-solvent-friction-000959nas a2200145 4500008004100000022001400041245011700055210006900172260011000241300001400351520027800365100002200643700001600665856013200681 2008 eng d a1359-734500aUnusual temperature dependence of salt effects for ``on water'' wittig reaction: hydrophobicity at the interface0 aUnusual temperature dependence of salt effects for on water witt aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcMAY a4445-44473 a

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

1 aTiwari, Shraeddha1 aKumar, Anil uhttps://library.ncl.res.in/content/unusual-temperature-dependence-salt-effects-water-wittig-reaction-hydrophobicity-interface-001433nas a2200157 4500008004100000022001400041245009300055210006900148260007100217300001600288490000800304520081500312100002201127700001601149856011001165 2009 eng d a1089-563900aInterfacial reactivity of ``on water'' reactions in the presence of alcoholic cosolvents0 aInterfacial reactivity of on water reactions in the presence of  a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcDEC a13685-136930 v1133 a

A detailed study of the variation in the interfacial reactivity and selectivity of ``on water'' reactions in the presence of increasing amounts of alcoholic cosolvents is discussed in the present work. The initial increase in the rates of ``on water'' 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 ``on water'' 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 ``signature'' characteristic for ``on water'' reactions is proposed.

1 aTiwari, Shraeddha1 aKumar, Anil uhttps://library.ncl.res.in/content/interfacial-reactivity-water-reactions-presence-alcoholic-cosolvents-001761nas a2200157 4500008004100000022001400041245007600055210006900131260007100200300001400271490000800285520116300293100002201456700001601478856010901494 2012 eng d a1089-563900aViscosity dependence of intra- and intermolecular diels-alder reactions0 aViscosity dependence of intra and intermolecular dielsalder reac a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcFEB a1191-11980 v1163 a

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.

1 aTiwari, Shraeddha1 aKumar, Anil uhttps://library.ncl.res.in/content/viscosity-dependence-intra-and-intermolecular-diels-alder-reactions-0