Characterizing Ionic Liquids as Reaction Media through a Chemical Probe

Abstract

The triplet N,N-dimethylaminophenyl cation, a highly reactive but chemospecific electrophile, has been used as a probe for characterizing the properties of reaction media for a series of imidazolium ILs. With the N-hexyl-N-methyl imidazolium derivatives (not with the N-butyl analogues), hydrogen transfer leading to the aniline was the main process. Trapping by iodide occurred with an inverse dependence on viscosity. Trapping by pi nucleophiles exhibited a more complex behavior. This was explained by the effect of both the bulk viscosity and the structure of the IL cation on both steps of the reaction, namely, initial electrophilic attack and ensuing cation elimination or nucleophile addition. However, with an excellent nucleophile, such as thiophene, or when the latter step was intramolecular, as with 4-pentenol, the difference was obliterated and trapping became uniform. Incorporation of the probe into the IL cation (through insertion into the C--H bond alpha to the imidazolium ring) was demonstrated, while no addition to the anion tested (including bis(trifluoromethanesulfonimide)) took place.

Photochemical Arylation of Alkenols: Role of Intermediates and Synthetic Significance

“…Irradiation of 1‐NMe 2 in MeCN/H 2 O (5:1) in the Presence of 3: A solution of 4‐chloro‐ N , N ‐dimethylaniline ( 1 ‐NMe 2 ; 233 mg, 1.5 mmol) and 4‐penten‐1‐ol ( 3 ; 1.53 mL, 15 mmol) in MeCN/H 2 O (5:1, 30 mL) was irradiated for 6 h. Purification by column chromatography (cyclohexane/ethyl acetate, 9:1) afforded a mixture of 2‐(4‐ N , N ‐dimethylaminobenzyl)tetrahydrofuran ( 6 ‐NMe 2 , 169 mg, 50 %) and 2‐(4‐ N , N ‐dimethylaminophenyl)tetrahydropyran ( 8 ‐NMe 2 , 5 %). Spectroscopic data of compounds 6 ‐NMe 2 and 8 ‐NMe 2 are in accordance with the literature data 43…”

Room Temperature Ionic Liquids: a “Green” Alternative to Conventional Organic Solvents?

“…These findings have been confirmed in a recent paper concerning the reaction of thioanisole with singlet oxygen ( 1 O 2 ) in pyrrolidinium-and imidazolium-based ILs [9]. In addition, the nonnegligible H-donor ability of the IL cation was once again confirmed [6][7][8][9][10]. In addition, product isotope effects suggest a different mechanism, changing from imidazolium to pyrrolidinium solvents [9].…”

“…2) [8]. In a recent study we have checked the stability of imidazoliumbased ILs in the presence of the photogenerated N,Ndimethylaminophenyl cation, an highly reactive electrophile [10]. In these solvents, thioanisole shows a strongly enhanced reactivity with respect to molecular aprotic solvents (benzene, MeCN) probably due to a stabilization of the persulfoxide intermediate in the ionic medium.…”

Viscosities and refractive indices of binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate with water at 298 K

“…The green character of RTILs has been justified with their air and water stability, their negligible vapour pressure (in normal temperature and pressure conditions) and their non-flammability [1][2][3][4][5]. The successful use of RTILs as solvent has been demonstrated for a wide range of chemical reactions [6] and industrial processes [7]. Thus, RTILs are considered as potential substitutes to many traditional solvents.…”