B(CF)-Catalyzed Dehydrogenation of Pyrrolidines to Form Pyrroles.

Pyrroles are important -heterocycles found in medicines and materials. The formation of pyrroles from widely accessible pyrrolidines is a potentially attractive strategy but is an underdeveloped approach due to the sensitivity of pyrroles to the oxidative conditions required to achieve such a transformation. Herein, we report a catalytic approach that employs commercially available B(CF) in an operationally simple procedure that allows pyrrolidines to serve as direct synthons for pyrroles.

Controlling the outcome of S2 reactions in ionic liquids: from rational data set design to predictive linear regression models.

Rate constants for a bimolecular nucleophilic substitution (SN2) process in a range of ionic liquids are correlated with calculated parameters associated with the charge localisation on the cation of the ionic liquid (including the molecular electrostatic potential). Simple linear regression models proved effective, though the interdependency of the descriptors needs to be taken into account when considering generality. A series of ionic liquids were then prepared and evaluated as solvents for the same process; this data set was rationally chosen to incorporate homologous series (to evaluate systematic variation) and functionalities not available in the original data set.

Resolving X-ray photoelectron spectra of ionic liquids with difference spectroscopy.

X-ray photoelectron spectroscopy (XPS) is a powerful element-specific technique to determine the composition and chemical state of all elements in an involatile sample. However, for elements such as carbon, the wide variety of chemical states produce complex spectra that are difficult to interpret, consequently concealing important information due to the uncertainty in signal identity. Here we report a process whereby chemical modification of carbon structures with electron withdrawing groups can reveal this information, providing accurate, highly refined fitting models far more complex than previously possible.

Correction: Rationalising the effects of ionic liquids on a nucleophilic aromatic substitution reaction.

Correction for 'Rationalising the effects of ionic liquids on a nucleophilic aromatic substitution reaction' by Rebecca R. Hawker et al., Org.

The effect of varying the anion of an ionic liquid on the solvent effects on a nucleophilic aromatic substitution reaction.

A variety of ionic liquids, each containing the same cation but a different anion, were examined as solvents for a nucleophilic aromatic substitution reaction. Varying the proportion of ionic liquid was found to increase the rate constant as the mole fraction of ionic liquid increased demonstrating that the reaction outcome could be controlled through varying the ionic liquid. The solvent effects were correlated with the hydrogen bond accepting ability (β) of the ionic liquid anion allowing for qualitative prediction of the effect of changing this component of the solute.

Rational selection of the cation of an ionic liquid to control the reaction outcome of a substitution reaction.

A range of ionic liquids was examined as solvents for a substitution reaction. They were chosen through rationally varying the ionic liquid cation in order to enhance the rate constant. Access to charge and electron-withdrawing substituents benefitted rate enhancement, allowing ionic liquids to be rationally selected to control reaction outcome.

Rationalising the effects of ionic liquids on a nucleophilic aromatic substitution reaction.

The nucleophilic aromatic substitution reaction between 1-fluoro-2,4-dinitrobenzene and ethanol was examined in a series of ionic liquids across a range of mole fractions. Temperature-dependent kinetic analyses were undertaken to determine the activation parameters for this reaction at the highest mole fraction. As the mole fraction of ionic liquid was increased, the rate constant of the reaction also increased, however the microscopic origin of the rate enhancement was shown to be different between different ionic liquids and also between different solvent compositions.

Novel Chloroimidazolium-Based Ionic Liquids: Synthesis, Characterisation and Behaviour as Solvents to Control Reaction Outcome.

Novel ionic liquids containing chlorine atoms on the imidazolium cation were synthesised. The physicochemical properties of these ionic liquids were investigated extensively, including glass transition, melting and decomposition temperatures, density, viscosity, miscibility with common solvents and electrochemical window. The behaviour of these ionic liquids as solvents was examined through temperature-dependent kinetic analyses on two reactions: a nucleophilic aromatic substitution (S Ar) reaction and a bimolecular nucleophilic substitution (S 2) reaction.

Probing the importance of ionic liquid structure: a general ionic liquid effect on an S(N)Ar process.

The effect of a range of ionic liquids, with systematic variations in the cation and anion, on the rate constant of an aromatic substitution process was investigated. Temperature-dependent kinetic data allowed calculation of activation parameters for the process in each solvent. These data demonstrate a generalised ionic liquid effect, with an increase in rate constant observed in each ionic solvent, though the microscopic origins of the rate constant enhancement differ with the nature of the ionic liquid.

Does the cation really matter? The effect of modifying an ionic liquid cation on an SN2 process.

The rate of reaction of a Menschutkin process in a range of ionic liquids with different cations was investigated, with temperature-dependent kinetic data giving access to activation parameters for the process in each solvent. These data, along with molecular dynamics simulations, demonstrate the importance of accessibility of the charged centre on the cation and that the key interactions are of a generalised electrostatic nature.