Daniela Millán

Mechanisms of Degradation of Paraoxon in Different Ionic Liquids

Herein, the reactivity and selectivity of the reaction of O,O-diethyl 4-nitrophenyl phosphate triester (Paraxon, 1) with piperidine in ionic liquids (ILs), three conventional organic solvents (COS), and water is studied by (31)P NMR, UV-vis, and GC/MS. Three phosphorylated products are identified as follows: O,O-diethyl piperidinophosphate diester (2), O,O-diethyl phosphate (3), and O-ethyl 4-nitrophenyl phosphate diester (4). Compound 4 also reacts with piperidine to yield O-ethyl piperidinophosphate monoester (5). The results show that both the rate and products distribution of this reaction depend on peculiar features of ILs as reaction media and the polarity of COS.

Toward a pKa Scale of N-base Amines in Ionic Liquids

An electrochemical technique was used to investigate pKa values of some substituted secondary alicyclic (SA) amines, pyridines (py), anilines (AN), and triethylamine (Et3N) in different ionic liquids. The method involves cyclic voltammetry at a platinized Pt electrode. The experimental data were correlated with pKa values reported previously in aqueous solution, and Hammett parameters were correlated with pKa values in ionic liquids to determine ρ values in these media.

Ionic liquids: anion effect on the reaction of O,O-diethyl O-(2,4-dinitrophenyl) phosphate triester with piperidine

The reactions of O,O-diethyl 2,4-dinitrophenylphosphate triester (1) with piperidine in ionic liquids and four conventional organic solvents (COS) were subjected to kinetic and product studies. Analytical techniques (UV-vis and NMR) identified two pathways: nucleophilic attack at the phosphoryl center and at the C-1 aromatic carbon. The nucleophilic rate constants (kTN) for these parallel reactions were separated into two terms: kPN and kArN for the corresponding electrophilic centers. Both the rate and the selectivities of the reactions are strongly dependent on the nature of the ionic liquid used, and a good correlation with the solvent acceptor capacity to form hydrogen bonds (β) was observed. Remarkably, an exclusive attack at the phosphoryl center was found using [Bmim]DCA, [Bmpyrr]DCA and [Bmpy]DCA as the reaction solvents. In contrast, with [Bmim]PF6 as the reaction solvent, attack at the C-1 aromatic was the main path (94%). These results suggest that ionic liquids can be considered to be designer solvents because by an appropriate choice of the anion it is possible to steer the selectivity of this reaction.

Influence of the ionic liquid on the rate and the mechanism of reaction of p-nitrophenyl acetate with secondary alicyclic amines†

The reaction of p-nitrophenyl acetate (1) with piperidine was studied in nine organic solvents and in nine ionic liquids. The aminolysis of 1 by four different secondary amines was also studied in [Bmim]BF4 and their basicities were determined in this solvent using two different methods. Medium effects were analysed and interpreted by comparing the rate constants of aminolysis for the two sets of solvents.

Solvatochromism and Halochromism of N-(4-Oxyphenyl) 5-nitro-2-thiophenecarboxaldimine

ABSTRACT The solvatochromic behavior of the title phenolate 1 was described and interpreted by means of theoretical calculations employing the PCM model and a TD-DFT method. The cationic halochromism of 1 was studied in DMSO and in ethanol solutions of LiClO4 and interpreted by a simple model that reproduced the variation of the charge-transfer transition energy of 1 with the cation concentration in solution.

Substituent effects on reactivity of 3-cinnamoylcoumarins with thiols of biological interest

The Michael addition reactions of the biothiols cysteine, homocysteine, cysteinyl-glycine, γ-glutamyl-cysteine and glutathione with 3-cinnamoylcoumarin derivatives (ChC1–ChC4) in aqueous solution (30 °C, ionic strength 0.2 M KCl) were followed fluorimetrically and evaluated kinetically. The study was completed with a theoretical analysis based on the inverse of the Fukui potential (1/νf (r)), which is proposed for the first time as a local softness descriptor. Thus, considering both experimental results and theoretical analysis, the following conclusions can be drawn: (i) the reactivity of the tested probes towards Michael addition increases in the para-substitution sequence: H < OEt < SMe < Br < NO2, and is not correlated with the σP values of the substituents; (ii) in turn, the descriptor proposed here as local softness (1/νf (r)) appears as a promising reactivity index that is able to explain the higher kN values found for both electron-withdrawing and electron-donating groups; (iii) the nucleophilic reactivity of the biothiols employed increases in the sequence Cys-Gly < Hcy < GSH < Cys < γ-Glu-Cys; and also finally (iv) we have demonstrated that these probes can be used for fluorimetric thiol determination in SH-SY5Y cells.

Preparation, spectroscopic and acidity properties of two hydrazones: an organic lab experiment

An undergraduate organic lab experiment is described based on the preparation of two readily accessible hydrazones. The UV-visible spectra of these N-H acids and of their conjugate bases are employed to illustrate the importance of through-conjugation in determining their acid strength and their internal charge-transfer-band transitions.

Theoretical substituent electrophilicities

A Hammett-like equation, relating theoretical global and substituent electrophilicities, is derived for substituted ethylenes and benzoic acids, allowing the calculation of electrophilic substituent constants σω. Correlations are given between the theoretical σω constants and kinetic or thermodynamic parameters of various chemical processes from the literature. Though electrophilic substituent constants are formally similar to the Hammett constants, they are derived from entirely different theoretical postulates. The similarities and differences between the two sets of constants are discussed and rationalized in terms of the definition of the electrophilic power of a chemical species.