Viscosity Dependence of Intra- and Intermolecular Diels–Alder Reactions

Abstract

The kinetics of the bimolecular Diels-Alder reaction between anthracene-9-carbinol and N-ethyl maleimide have been studied in a series of pyridinium-based ionic liquids with the tetrafluoroborate ([BF(4)](-)) and the bis(trifluorosulfonimide) ([NTf(2)](-)) 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.

Binary mixtures of ionic liquids-DMSO as solvents for the dissolution and derivatization of cellulose: Effects of alkyl and alkoxy side chains

“…Lower viscosity is expected to favor cellulose dissolution and derivatization. This expectation (rate increase as a function of decreasing medium viscosity) was verified experimentally for reactions of isomerization (Baba et al, 2006) and Diels-Alder (Khupse & Kumar, 2011;Tiwari & Kumar, 2012) in pure ILs and their mixtures with MSs.…”

Probing Cellulose Acetylation in Binary Mixtures of an Ionic Liquid with Dimethylsulfoxide and Sulfolane by Chemical Kinetics, Viscometry, Spectroscopy, and Molecular Dynamics Simulations

“…[ 10 ] It should affect the reaction rate favorably due to the concomitant increase in reactant diffusion coeffi cient ( D ), as indicated by the Stokes-Einstein equation: D = k B T /6π ηa , where k B and a refer to the Boltzmann constant and particle radius, respectively. [ 12 ] This expectation (rate increases as a function of decreasing medium viscosity) has been verifi ed experimentally for reactions in pure ILs, [ 13,14 ] and their mixtures with MSs. [ 15 ] Finally, the use of IL/MS mixtures lowers process cost, leads to better mass and heat transfers, and overcomes solubility problems, e.g., of the cellulose derivatizing reagent, or the produced cellulose derivative.…”

A Joint Action of Deep Eutectic Solvents and Ultrasound to Promote Diels–Alder Reaction in a Sustainable Way

“…From a mechanistic point of view, its pathway is well understood in conventional solvents. − It proceeds in a single step through a cyclic transition state and consequently can be used for evaluating solvent effects. For this reason, it has been performed in water and fluorous solvents, as well as ionic liquids (ILs) , and ionic liquid mixtures …”

“…7−9 It proceeds in a single step through a cyclic transition state and consequently can be used for evaluating solvent effects. For this reason, it has been performed in water 10 and fluorous solvents, 11 as well as ionic liquids (ILs) 12,13 and ionic liquid mixtures. 14 In the context of planning more environmentally friendly synthetic strategies, also the solvent choice represents an important concern.…”