Search

This review illustrates how ionic liquid properties can affect Diels–Alder reactions. The mechanisms by which ionic solvents enhance the rate and selectivity of the reaction are discussed on the basis of correlation studies using empirical parameters and theoretical calculations. [ABSTRACT FROM AUTHOR]

As the interest for environmental increases and environmental laws become more stringent, the need to replace existing processes with new more sustainable technologies becomes a primary objective. The use of ionic liquids to replace organic solvents in metal catalyzed reactions has recently gained much attention and great progress has been accomplished in this area in the last years. This paper reviews the recent developments in the application of ionic liquids and related systems (supported ionic liquids, ionic polymers, and so on) in the Heck reaction. Merits and achievements of ionic liquids were analyzed and discussed considering the possibility of increasing the effectiveness of industrial processes. [ABSTRACT FROM AUTHOR]

High-yield reactions of the pentafluoride complexes MF5 (M=Nb, Ta) with a variety of diethers, ROCH2CH(R')OR", afford the ionic derivatives [MF4(K2-ROCH2CH(R')OR")2][MF6] (2a-2e) or [MF4(ROCH2CH(R')OR" )2][M2F11] (3a-3f) according to the metal/diether ratio employed. The structures of [MF4(K2-dme)2][MF6] [M=Nb (2a), Ta (2b); dme=MeOCH2CH2OMe] have been determined by X-ray diffraction. Moreover, the structure of the cationic part of 2a in the gas phase has been optimized by density functional theory calculations (the B3LYP/LANL2DZ method). An analogous computational study has allowed one to predict the existence of a heptacoordinated niobium cation within the species [NbCI4(dme)2][NbCl6]. This prediction has been confirmed by NMR identification at -60°C of the complexes [MCI4(K2-dme)(K1-dme)][MCI6] [M=Nb (4a), Ta (4b)], obtained by the addition of dme to MCI5 in CDCI3. Activation of the coordinated diether in 2 and 3 takes place in solution at high temperature and generally proceeds via cleavage of C-C bonds and coupling of the fragments produced. Thus, OR2 (R=Me, Et) and 1,4-dioxane have been obtained selectively upon thermal reaction of MF5 with rime, diglyme, or 1,2-diethoxyethane, followed by treatment with water. In analogous conditions, 1,2-dimethoxypropane converts mainly into acetone and dimethyl ether. The formation of dioxane from dme occurs in high yield also by using a catalytic amount of NbF5. The activation of dme by NbF5 follows a pathway different from that previously reported for NbCI5, and an explanation based on the thermodynamic parameters calculated at the B3LYP/LANL2DZ level is given: the formation of Me2O and dioxane is the most favored reaction between NbF5 and dme (ΔGr°= -15.16 kcal ∙ molNb-1), while the formation of MeCl and dioxane is the most favored reaction in the case of NbCl5/dme (ΔGr°=-53.13 kcal ∙ molNb-1). [ABSTRACT FROM AUTHOR]

Abstract: The ionization of chlorobis(4-methoxyphenyl)methane ( 1-Cl ) was performed in 1:1 mixtures of TFE/ILs (ILs=[emim][Tf2N], [bmim][Tf2N], [bpy][Tf2N]), and TFE/CH3CN. The decay of the immediately formed carbenium ion 1 + was followed by stopped flow, showing that the lifetime of this intermediate significantly decreases on going from CH3CN to [emim][Tf2N]. Ab initio calculations suggest an increase in the electrophilicity of the carbenium ion in ILs. [Copyright &y& Elsevier]

Review: [158 refs. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this work was to investigate innovative reaction media such as ionic liquids for enzymatic phospholipids transformations in order to get a higher selectivity in the enzymatic transphosphatidylation reactions of natural phosphatidylcholine catalyzed by phospholipase D (PLD) from Streptomyces PMF. The stability and the activity of the PLD in the ionic liquid [BMIM][PF6] were tested. This ionic liquid used as a cosolvent in the synthesis of phosphatidylserine lead surprisingly to the almost quantitative suppression of unwanted hydrolytic side reaction, thus providing a great improvement in the final product purification. [Copyright &y& Elsevier]

While the solvent effect on the rate of tautomerization of 2-nitrocyclohexanone in several organic solvents appears to depend essentially on the permittivity of the solvent, a different behavior is observed in some ionic liquids. In particular the rate of the reaction in ionic liquids (ILs) is much faster than expected solely on the basis of the permittivity of the studied ILs. However, if more solvent parameters are taken into consideration (namely the polarizability, H-bond acidity, and cohesive pressure of the solvent) one comprehensive linear solvation energy relationship (LSER) for both organic and IL media can be obtained and no special "ionic liquid effect" can be highlighted. The kinetic results have also been discussed in terms of the Brønsted equation. It turns out that on passing from molecular solvents to IL5 the transition state structure of the enolization reaction becomes markedly enolate-like (Brønsted β value close to 1). [ABSTRACT FROM AUTHOR]

The first study of a copper(I)-catalyzed azide-alkyne click reaction in ionic liquids (ILs) is reported. The cycloaddition of a sugar azide with a sugar acetylene (CuI, i-Pr2EtN, 80 °C) was carried out in 10 ILs as well as in standard molecular solvents (toluene and DMF) to give the 1,4-disubstituted triazole-linked C-disaccharide. The highest yields (84 and 95%) were registered in Ammoeng 110 and [C8dabco][N(CN)2]. The latter solvent was recycled in four subsequent reactions without loss of the reaction efficiency. Reactions carried out in the absence of the Hünig's base afforded mixtures of 1,4- and 1,5-disubstituted triazole regioisomers. [ABSTRACT FROM AUTHOR]

A tetra-azido calix[4]arene derivative was allowed to react with ethynyl tetra-O-benzyl-C-galactoside in the presence of CuI and i-Pr2EtN in three different ionic liquids, that is, [C8dabco][N(CN)2], [C8dabco][Br], and Ammoeng 110. Reactions were performed at 80 °C by thermal and MW dielectric heating. In all cases, multiple cycloadditions took place to give a triazole-linked tetra-C-galactosyl-calix[4]arene in up to 90% yield. The [C8dabco][N(CN)2] ionic liquid was also used to perform the multiclick reactions with propargyl O-lactoside and S-sialoside. [ABSTRACT FROM AUTHOR]