1,720,996 research outputs found
Regioselective iodination of arenes in ionic liquids mediated by the Selectfluor (TM) reagent F-TEDA-BF4
No full textA variety of aromatic compounds was regioselectively iodinated with iodine and F-TEDA in imidazolium- and pyridinium-based ionic liquids, [bmim][PF6] and [bpyr][BF4]. Iodination was para- directed when possible, otherwise it occurred in the ortho- position. The substrate selectivity measured in competitive experiments is in agreement with a polar mechanism
Direct mono-N-alkylation of amines in ionic liquids: chemoselectivity and reactivity
No full textA simple method for the N-alkylation of primary amines was developed using ionic liquids as solvent in order to prepare secondary amines selectively. In ionic liquids overalkylation of the initially produced secondary amines is in general markedly reduced. Various amines, alkyl halides and sulfonates were examined. The observed selectivities between mono- and dialkylation are typically on the order of 9+1, or higher. Only in the cases of allyl or benzyl bromides does the reaction give the corresponding tertiary amines exclusively. The relative nucleofugality of chloride, bromide, iodide and tosylate with several primary amines was also evaluated, as well as the effect of caesium hydroxide
Determination of ionic liquids solvent properties using an unusual probe: The electron donor-acceptor complex between 4,4 '-bis(dimethylamino)-benzophenone and tetracyanoethene
No full textMichler's ketone (MK) and tetracyanoethene (TCNE) may be used as a UV-vis probe to investigate the solvent properties of ionic liquids (ILs). In molecular solvents, MK and TCNE give an electron donor-acceptor (EDA) complex, a zwitterionic species or a radical ion pair, depending on the aprotic or protic nature of the solvent and on its ionizing power. In agreement with the behavior observed in aprotic solvents, only the EDA complex was detected in ILs bearing low donor anions (beta < 0.7). The formation constant determined in [bmim][Tf(2)N] (K(c) = 5.6 (0.5) M(-1)) is similar to that measured in 1,2-dichloroethane at 25 degrees C. The visible absorption maximum (nu(max,CTC)) of the EDA complex is quantitatively described by a multiple correlation using the Kamlet-Taft pi*, beta, and alpha parameters of the solvents. The H-bond donating capacity of ILs is not sufficient to determine the transformation of the EDA complex into the zwitterionic species, but the Kamlet-Taft alpha parameter seems to affect the position of the absorption band. The high ionization power of ILs, moreover, favors the slow dissociation of the EDA complex into its corresponding radical ion pair; this behavior generally characterizes highly polar and highly ionizing protic solvents, such as TFE and HFI. Finally, since the formation of the EDA complex is strongly affected by the presence of impurities, traces of nucleophiles (chloride or amines) or water may be easily detected through the change of the solution color
Kinetic study of the addition of trihalides to unsaturated compounds in ionic liquids. Evidence of a remarkable solvent effect in the reaction of ICl2-
No full textThe kinetic constants and activation parameters for the reactions of Br-3(-) and ICl2- with some alkenes and alkynes have been determined in the ionic liquids [bmim] [PF6], [emim] [Tf2N], [bmim] [Tf2N], [hmim] [TF2N], [bm(2)im] [Tf2N], and [bpy] [TF2N] (where emim = 1-ethyl-3-methylimidazolium, bmim = 1-butyl-3-methylimidazolium, hmim = 1-hexyl-3-methylimidazolium, bm(2)im = 1-butyl-2,3-dimethylimidazolium, bpy = butylpyridinium, PF6 = hexafluorophosphate, and Tf2N = bis(trifluoromethylsulfonyl)imide) and in 1,2-dichloroethane. The rates of both reactions increase on going from 1,2-dichloroethane to ILs. Evidence suggests that, while the hydrogen bonding ability of the imidazolium cation is probably the main factor able to increase the rate of the addition of ICl2- to double and triple bonds, this property has no effect on the electrophilic addition of Br-3(-) to alkenes and alkynes. Furthermore, in the case of the ICl2- reaction, the hydrogen bonding ability of ILs can be exploited to suppress the unwanted nucleophilic substitution reaction on the products by the Cl- anion
Bromination of Alkynes in Ionic Liquids - A Kinetic Investigation
No full textThe kinetic behaviour and the product distributions of brominations of several arylalkynes with Br2 in the room-temperature ionic liquids (ILs) 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] and 1-butyl-3-methylimidazolium bromide [bmim][Br], have been investigated at different temperatures. In [bmim][Br], alkynes stereospecifically gave the anty addition products, the reactions following a second-order rate law.In [bmim][PF6], mixtures of syn and anti addition products were obtained, and the reaction followed a second- or third-order rate law, depending on the structure of the alkyne and the concentration of Br2. The data obtained for the reactions in [bmim][Br] are interpreted on the basis of a mechanism involving a product- and a rate-determining nucleophilic attack by bromide on the alkyne-Br2 Π complex. The data relating to the electrophilic addition in [bmim][PF6] are explained in terms of the initial 1:1 alkyne-Br2 Π complex, the ionisation of which, probably catalysed either by a second halogen molecule or by the imidazolium cation, gives a bromirenium (or β-bromovynil cation) Br- or [Br3]- intermediate. Such intermediates then collapse to give the corresponding dibromo adduct(s). The kinetic constants and the activation parameters for the reaction in [bmim][Br] are compared with those relating to the second-order reaction of the same alkynes with tetrabutylammonium tribromide ([NBu4][Br3]) in 1,2-dichloroethane (DCE). On the basis of the kinetic data, a significant role for solvent viscosity in determining the reaction rate may be envisaged
Bromination of alkynes in ionic liquids - A kinetic investigation
No full textThe kinetic behaviour and the product distributions of brominations of several arylalkynes with Br(2) in the room-temperature ionic liquids (ILs) 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF(6)] and 1-butyl-3-methylimidazolium. bromide [bmim]Br, have been investigated at different temperatures. In [bmim]Br, alkynes stereospecifically gave the anti addition products, the reactions following a second-order rate law. In [bmim][PF(6)], mixtures of syn and anti addition products were obtained, and the reactions followed a second- or third-order rate law, depending on the structure of the alkyne and the concentration of Br(2). The data obtained for the reactions in [bmim]Br are interpreted on the basis of a mechanism involving a product- and a rate-determining nucleophilic attack by bromide on the alkyne-Br(2) pi complex. The data relating to the electrophilic addition in [bmim][PF6] are explained in terms of the initial formation of a 1:1 alkyne-Br(2) pi complex, the ionisation of which, probably catalysed either by a second halogen molecule or by the imidazolium cation, gives a bromirenium (or beta-bromovinyl cation) Br(-) or [Br(3)](-) intermediate. Such intermediates then collapse to give the corresponding dibromo adduct(s). The kinetic constants and the activation parameters for the reaction in [bmim]Br are compared with those relating to the second-order reaction of the same alkynes with tetrabutylammonium tribromide ([NBu(4)][Br(3)]) in 1,2-dichloroethane (DCE). On the basis of the kinetic data, a significant role for solvent viscosity in determining the reaction rate may be envisaged. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
Highly efficient bromination of aromatic compounds using 3-methylimidazolium tribromide as reagent/solvent
No full text3-Methylimidazolium tribromide proves to be an alternative highly efficient reagent/solvent for the halogenation of nonactivated aromatic compounds
Application of hydrophilic ionic liquids as co-solvents in chloroperoxidase catalyzed oxidations
No full textThe effect of hydrophilic ionic liquids (ILs) on the activity of chloroperoxidase (CPO) was checked through kinetic and stereochemical studies. The possibility to employ this enzyme in synthesis has been demonstrated investigating the chemo- and stereo selectivity of oxidation of phenyl methylsulfide in several citrate buffer-IL mixtures. (c) 2006 Elsevier Ltd. All rights reserved
Trihalide-based imidazolium salts as versatile reagents for the halogenation of unsaturated compounds in ionic liquids
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