ABSTRACT
In this paper, we report the effect of ionic liquids on substitution reactions using a variety of anionic nucleophiles. We have combined new studies of the reactivity of polyatomic anions, acetate, trifuoroacetate, cyanide, and thiocyanide, with our previous studies of the halides in [C4C1py][Tf2N], [C4C1py][TfO], and [C4C1im][Tf2N] (where [C4C1im]+ is 1-butyl-3-methylimidazolium and [C4C1py]+ is 1-butyl-1-methylpyrrolidinium) and compared their reactivities, k2, to the same reactions in the molecular solvents dichloromethane, dimethylsulfoxide, and methanol. The Kamlet-Taft solvent descriptors (alpha, beta, pi) have been used to analyze the rates of the reactions, which were found to have a strong inverse dependency on the alpha value of the solvent. This result is attributed to the ability of the solvent to hydrogen bond to the nucleophile, so reducing its reactivity. The Eyring activation parameters (DeltaH++ and DeltaS++), while confirming the reaction mechanism, do not offer obvious correlations with the Kamlet-Taft solvent descriptors.
ABSTRACT
In this work we have examined the nitration by acetyl nitrate of a range of activated and deactivated aromatic substrates in two ionic liquids and compared the results to the same reaction in dichloromethane. Both ionic liquids are stable to the reaction conditions, and in both ionic liquids the yields of reaction are higher after unit time than the same reactions in dichloromethane, although the regioselectivity is little affected by solvent choice. This result gives further support to the suggestion that in the ionic liquid, acetyl nitrate dissociates to give the nitronium ion, and that this is the effective nitrating agent here. However, it is shown that [bmpy][N(Tf)(2)] is a better solvent for aromatic nitration than [bmpy][OTf]. This is due to the ease of formation of nitronium ion in the former ionic liquid, and is consistent with the fact that [bmpy][N(Tf)(2)] is a weaker hydrogen bond acceptor solvent than [bmpy][OTf]. Finally, a method by which [bmpy][N(Tf)(2)] may be recovered and reused for aromatic nitration has been demonstrated.
ABSTRACT
Microfluidic devices for spatially localised heating of microchannel environments were designed, fabricated and tested. The devices are simple to implement, do not require complex manufacturing steps and enable intra-channel temperature control to within +/-0.2 degrees C. Ionic liquids held in co-running channels are Joule heated with an a.c. current. The nature of the devices means that the internal temperature can be directly assessed in a facile manner.
Subject(s)
Ions/chemistry , Microfluidics/instrumentation , Temperature , Equipment Design , Imidazoles/chemistry , Microfluidics/methodsABSTRACT
We have continued the study of halide nucleophilicity in ionic liquids, concentrating on the effect of changing the anion ([BF(4)](-), [PF(6)](-), [SbF(6)](-), [OTf](-), and [N(Tf)(2)](-)) when the cation is [bmim](+) (where bmim = 1-butyl-3-methylimidazolium). It was found that the nucleophilicities of all the halides were lower in all of the ionic liquids than in dichloromethane. Changing the anion affected the order of halide nucleophilicity, e.g., in [bmim][BF(4)] the order of nucleophilicity was Cl(-)>Br(-)>I(-) while in [bmim][N(Tf)(2)] the order was Cl(-)
ABSTRACT
In this work we report the effect of ionic liquids on a class of charge-neutral nucleophiles. We have studied the reactions of (n)butylamine, di-(n)butylamine, and tri-(n)butylamine with methyl p-nitrobenzenesulfonate in [bmpy][N(Tf)(2)], [bmpy][OTf], and [bmim][OTf] (bmpy = 1-butyl-1-methylpyrrolidinium; bmim = 1-butyl-3-methylimidazolium) and compared their reactivities, k(2), to those for the same reactions in the molecular solvents dichloromethane and acetonitrile. It was shown that all of the amines are more nucleophilic in the ionic liquids than in the molecular solvents studied in this work. Comparison is also made with the effect of ionic liquids on the reactivity of chloride ions, which are deactivated in ionic liquids. The Eyring activation parameters revealed that changes in the activation entropies are largely responsible for the effects seen. This can be explained in part by the differing hydrogen-bonding properties, as shown by the Kamlet-Taft solvent parameters, of each of these solvents and the formation of hydrogen bonds between the solvents and the nucleophiles.
ABSTRACT
Aromatic substrates can be nitrated in high yields and with efficient use of the nitrating agent in ionic liquids, although a suitably inert ionic liquid cation must be used.
ABSTRACT
In this work, the nucleophilicities of chloride, bromide, and iodide have been determined in the ionic liquids [bmim][N(Tf)(2)], [bm(2)im][N(Tf)(2)], and [bmpy][N(Tf)(2)] (where bmim = 1-butyl-3-methylimidazolium, bm(2)im = 1-butyl-2,3-dimethylimidazolium, bmpy = 1-butyl-1-methylpyrrolidinium, and N(Tf)(2) = bis(trifluoromethylsulfonyl)imide). It was found that in the [bmim](+) ionic liquid, chloride was the least nucleophilic halide, but that changing the cation of the ionic liquid affected the relative nucleophilicities of the halides. The activation parameters DeltaH(), DeltaS(), and DeltaG() have been estimated for the reaction of chloride in each ionic liquid, and compared to a similar reaction in dichloromethane, where these parameters were found for reaction by both the free ion and the ion pair.
