Spectacular Rate Enhancement of the Diels–Alder Reaction at the Ionic Liquid/n‐Hexane Interface

Abstract

The use of the ionic liquid/n-hexane interface as a new class of reaction medium for the Diels-Alder reaction gives large rate enhancements of the order of 10(6) to 10(8) times and high stereoselectivity, as compared to homogeneous media. The rate enhancement is attributed to the H-bonding abilities and polarities of the ionic liquids, whereas the hydrophobicity of ionic liquids was considered to be the factor in controlling stereoselectivity.

Solvophobic Acceleration of a Diels–Alder Reaction in True Solutions in Organic Solvents

“…Fluorinated hydrocarbons also can significantly speed up cycloaddition, which was called “fluorophobic” acceleration . Recently, dramatic acceleration of the rate of the Diels‐Alder reaction was observed at the interface of n ‐hexane with imidazolium‐based ionic liquids .…”

“…A solvent‐induced increase in the rate of cycloaddition can be caused by different types of interactions. In ionic liquids, it was attributed to stabilization of transition state by hydrogen bonding and ion–dipole interactions, whereas in perfluorocarbons it can be explained by reduction of the solvent‐accessible surface area engaged in unfavorable interactions with the solvent upon formation of the transition state. In aqueous solutions, hydrogen bonds formed by reactants and transition state with water undoubtedly influence the reaction rate , but the proof of the key role of the hydrophobic effect arises from the observations that (1) in water, the Diels–Alder reaction can be many times faster in comparison with other H‐donor solvents such as methanol; (2) additives that are known to strengthen the hydrophobic effect speed up cycloaddition, whereas those suppressing the hydrophobic effect such as guanidinium chloride slows down the reaction.…”

Interfacial Polymerization at the Alkane/Ionic Liquid Interface

“…[15] Their fascinating nature makes it possible to dissolve various aromatic amines while forming stable interfaces with alkanes. [16,17] Such anhydrous interfaces can thoroughly avoid the hydrolysis of acyl chloride during interfacial polymerization. Herein, we report as eries of alkane-IL interfaces,i n which ILs act as universal solvents for diversified amine monomers,t os ynthesize polyamide nanofilms by the interfacial polymerization between the amine and trimesoyl chloride (TMC) (Figure 1).…”

Interfacial Polymerization at the Alkane/Ionic Liquid Interface

“…They possess a set of intriguing merits such as extremely low vapor pressure, high stability, powerful solvency, and rich designability [15] . Their fascinating nature makes it possible to dissolve various aromatic amines while forming stable interfaces with alkanes [16, 17] . Such anhydrous interfaces can thoroughly avoid the hydrolysis of acyl chloride during interfacial polymerization.…”