Stella M. Chiacchiera

Universidad Nacional de Río Cuarto, Río Cuarto, Provincia de Cordoba, Argentina

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Publications (8)13.84 Total impact

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    ABSTRACT: Phase-transfer catalysis (PTC) is a widely accepted methodology in organic synthesis. Although a great number of organic syntheses were reported in PTC conditions, systematic kinetic studies are scarce. In the present report, a detailed study of the kinetics of the reaction between 2-chloro-5-nitrotrifluoromethylbenzene (CNTFB) and 2-phenylpropionitrile anion (HPP-), under PTC, was performed under several conditions. The reaction was carried out either in toluene or chlorobenzene as the organic phase, in the presence of a concentrated aqueous solution of NaOH using tetraalkylammonium (Q+X-) salts as phase-transfer catalysts. The major product was 2-(4-nitro-2-trifluoromethylphenyl)-2-phenylpropionitrile, and its yield depends on the experimental conditions. Different aspects of the mechanism are discussed and quantified. Kinetic data were explained by means of an interfacial mechanism that involves the deprotonation of the adsorbed nucleophile precursor followed by its catalyst-mediated extraction to the organic phase. A multicomponent Langmuir-type interface was assumed. Although the extraction of OH- by catalyst to the organic phase is usually disregarded, the formation of the substrate hydrolysis product that leads to catalyst poisoning was also investigated. The influence of this side reaction on the yield of the main product was established. A discussion about the influence of this side process on the main reaction and the operating mechanism is presented.
    The Journal of Organic Chemistry 07/2005; 70(12):4659-66. · 4.56 Impact Factor
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    ABSTRACT: The distribution of different aliphatic and aromatic amines: n-butylamine (n-BA), isobutylamine (i-BA), tert-butylamine (t-BA), piperidine (PIP), N,N-dimethylaniline (DMA) and N-methylaniline (MA) in water/sodium 1,4-bis(2-ethylhexyl)sulfosuccinate(AOT)/n-hexane reverse micelles was investigated by steady-state fluorescence measurements. The partition constants were measured by an indirect method based on the effect that amine partitioning exert on the bimolecular rate of the reaction between a microphase incorporated fluorophore (Ru(bpy)2+(3)) and the quencher, (Fe(CN)3-(6)). For MA, that can act as a quencher of the fluorophore a direct method was used. The results show that primary amines have larger partition constants than the secondary ones. For tertiary amines the distribution constants were practically negligible. Laser flash photolysis experiments confirmed that tertiary amines, both aliphatic and aromatic, are not incorporated to the micellar pseudophase. The effect of the amine structure on the partition constant was analyzed through linear solvation free energy relationships (LSER) using solute parameters and compared with those obtained for alcohols. Hydrogen bond interactions with the AOT polar heads appear to be the main driving force for the distribution of amines between the organic and micellar pseudophases, whereas the size of the alkyl or aromatic group tends to hinder it.
    Journal of Colloid and Interface Science 07/2005; 286(1):245-52. · 3.55 Impact Factor
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    ABSTRACT: The kinetics of the aromatic nucleophilic substitution (SNAr) reactions of 1,2-dinitrobenzene (1,2-DNB) with butylamine (BA) and piperidine (PIP) were investigated as a function of the amine concentration and temperature, in chloroform, ethyl acetate, tetrahydrofuran (THF), acetonitrile (ACN), dimethylformamide (DMF), dimethyl sulphoxide (DMSO). benzene, toluene, chlorobenzene and diisopropyl ether.In the set of solvents consisting of ethyl acetate, THF, ACN, DMF and DMSO, neither reaction is catalysed (kA = k1). The sequence and range of reactivity for BA and PIP are similar in these solvents. These results indicate that reactions in which nitro in the leaving group behave differently from SNAr reactions with other leaving groups, such as halogens or alkoxy groups, since an intramolecular hydrogen bond may be expected between the leaving nitro group and the ammonium H of the nucleophiles. The correlations of the rate coefficients obtained with Taft and Kamlet's solvatochromic method support these conclusions.On the other hand, these reactions show mild acceleration with relatively non-polar solvents such as the aromatics and diisopropyl ether. The donor properties of these solvents and experiments with solvent mixtures suggest the formation of electron donor–acceptor complexes between them and 1,2-DNB. Hence the preferential solvation of 1,2-DNB by the donor solvent accounts for the mechanism observed.
    Journal of Physical Organic Chemistry 10/2004; 2(8):631 - 645. · 1.58 Impact Factor
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    ABSTRACT: The kinetic profile of the S N Ar reaction of 1-chloro-2,4-dinitrobenzene with n-butylamine and piperidine in AOT/n-hexane/water reverse micelles were investigated as a function of variables such as AOT and amine concentration and the amount of water dispersed in the reverse micelles, W o = [H 2 O]/[AOT]. The reactions in the micellar medium are faster than in the pure solvent. The pseudo-first order rate constants of the reactions go through a maximum when the AOT concentration is increased. Micellar interface saturation and no further micellar catalysis occurs at c.a. 0.1M of AOT. At higher AOT concentration dilution of the reactants in the micelles is the responsible of the rate decrease. In micellar medium a significant lost in the catalysis is observed compare with pure n-hexane. Thus, the reactions effectively take place at the interface of the aggregates. The kinetic behavior can be quantitatively explained taking into account the distribution of the substrate and the nucleophile between the bulk solvent and the micelle interface. A plausible mechanism to explain the results is proposed. Both the reactants distribution constants, between the micellar pseudo-phase and organic solvent, and the intrinsic second-order rate coefficients of S N Ar reactions in the interface were evaluated.
  • Edgardo N. Durantini, Stella M. Chiacchiera, Juana J. Silber
    Journal of Organic Chemistry - J ORG CHEM. 04/2002; 58(25).
  • Milanesio E, S. M. Chiacchiera, J. J. Silber, E N Durantini
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    ABSTRACT: A convenient procedure for the synthesis of 5-(4-acetamidophenyl)-10,15,20-tris(4-substituted phenyl) porphyrins from dipyrrolomethane is reported. meso-(4-Substituted phenyl) dipyrrolomethanes were obtained in yields of 72-84%. The amide porphyrins were isolated with appreciable yields of 15-17%.
    Molecules. 01/2000;
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    ABSTRACT: The reaction of tricarbonyl[η6-2-chloro-1-(trifluoromethyl)benzene]chromium with in situ generated phenylacetonitrile anion affords two diastereomeric products, which yield α-phenyl-α-[2-(trifluoromethyl)phenyl]acetonitrile upon decomplexation. The SNAr intrinsic rate constant was evaluated, and the activation of the tricarbonylchromium moiety was compared with that of the nitro group.
    Organometallics 01/1999; 18(14):2727-2730. · 4.15 Impact Factor
  • Edgardo N. Durantini, Stella M. Chiacchiera, Juana J. Silber
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    ABSTRACT: A convenient procedure for the synthesis of N-[(trifluoromethyl) nitrophenyl] substituted anilines by means of a chloro-substitution reaction under conditions of phase-transfer catalysis (PTC) is reported. The ipso-substitution product is obtained with high yield. This method provides a general procedure for the synthesis of diphenylamines bearing electron-withdrawing groups in both aromatic rings.
    ChemInform 01/1996; 26(20):3849-3858.