25832-66-0Relevant academic research and scientific papers
Electronic and steric effects: How do they work in ionic liquids? the case of benzoic acid dissociation
D'Anna, Francesca,Marullo, Salvatore,Vitale, Paola,Noto, Renato
, p. 4828 - 4834 (2010)
(Figure Presented) The need to have a measure of the strength of some substituted benzoic acids in ionic liquid solution led us to use the protonation equilibrium of sodium p-nitrophenolate as a probe reaction, which was studied by means of spectrophotometric titration at 298 K. In order to evaluate the importance of electronic effect of the substituents present on the aromatic ring, both electron-withdrawing and -donor substituents were taken into account. Furthermore, to have a measure of the importance of the steric effect of the substituents both para- and ortho-substituted benzoic acids were analyzed. The probe reaction was studied in two ionic liquids differing for the ability of the cation to give hydrogen bond and π-π interactions, namely [bm 2im][NTf2] and [bmpyrr][NTf2]. Data collected show that benzoic acids are less dissociated in ionic liquid than in water solution. Furthermore, the equilibrium constant values seem to be significantly affected by both the nature of ionic liquid cation and the structure of the acid. In particular, the ortho-steric effect seems to operate differently in water and in the aromatic ionic liquid, determining in this solvent medium a particular behavior for ortho-substituted benzoic acids.
Mechanism and models for homogeneous copper mediated ligand exchange reactions of the type: CuNu + ArX (*) ArNu + CuX
Couture, Christiane,Paine, Anthony James
, p. 111 - 120 (2007/10/02)
The title reactions are an important class of copper mediated nucleophilic aromatic substitution processes, which constitute a useful tool in the molecular design and synthesis of small molecules.We report the results of extensive investigation of these processes, primarily focussing on cyanodeiodination (ArI + CuCN CuI + ArCN).Among the interesting features of these processes are: (a) an unusual rate equation involving autocatalysis by CuI product; (b) retardation by both excess nucleophile (as KCN) and excess leaving group (as KI), which complete with ArX to complex with CuNu; (c) only cuprous nucleophiles are active (ligand exchanged products from cupric salts arise from prior redox equilibria which form CuNu); (d) the halogen effect is large (kI ca 40 - 100 kBr ca 300 - 5000 kCl) but the Hammett q value is zero; (e) ortho-alkyl groups do not hinder the reaction ( and actually cause mild acceleration by relief of steric strain).Finally, the introduction of an ortho-COO- group accelerates the reaction by a factor of 104 - 105 , but the general features of the accelerated reactions are also the same, again indicating a common mechanism, with entropic acceleration by ortho-carboxylate.Both kinetic and thermodynamic factors were considered in detail, the latter apparently for the first time.Applications to practical syntheses are considered, and novel mechanistic models for these interesting processes are discussed.
