The kinetics of the reactions between 1-halogeno-2,4-dinitrobenzene (halogen ¼ F, Cl) and the amines ethylenediamine (EDA) and 3-dimethylamino-1-propylamine (DMPA) were studied in toluene at 25 AE 0.2C under pseudo-first-order conditions using varying amounts of amine. Even with Cl as the nucleofugue (where usually the first step is rate-determining), a third-order-in-amine kinetic law was observed: these results can be interpreted within the 'dimer nucleophile' mechanism where the amine homo-aggregates are better nucleophiles than the amine monomers. To confirm this interpretation, the reaction of 2,4-dinitrofluorobenzene with histamine was studied in the same solvent. Because of the rigid geometry, an intramolecular hydrogen bond is easily established, which prevents the formation of self-aggregates. Consequently, the plot of k A vs.[histamine] is a straight line, as expected for a classical mechanism of base-catalysed decomposition of the zwitterionic intermediate. All these results are well explained in the frame of the 'dimer nucleophile' mechanism.

The kinetics of the reaction of aniline with 2,4-dinitrochlorobenzene (2,4-DNClB) were studied in several benzene-nhexane mixtures at 40 ЊC in the presence of variable amounts of aniline. A linear dependence of the second-order rate coefficients, k A , with [B] is observed, with a null intercept. Taking into account the non-polar character of the solvent, and the excellent nucleofugacity of chlorine, this kinetic behaviour is interpreted as evidence of the aggregation of aniline, the hydrogen-bonded dimer acting as the nucleophile. Consistent with this interpretation, when the solvent is changed to THF, a good hydrogen-bond acceptor (HBA), the k A is no longer dependent on [B]. Electron donoracceptor (EDA) molecular complexes of 2,4-DNClB with benzene and with aniline, and also between aniline and the product, were clearly recognized and the stability constants of each one of these complexes were determined.

Inter-and intramolecular hydrogen bonding play an important role in determining the arrangement, physical properties, and reactivity of a great diversity of structures in chemical and biological systems. Several aromatic nucleophilic substitutions (ANS) in nonpolar aprotic, (non-HBD), solvents recently studied in our laboratory have demonstrated the importance of self-association of amines by hydrogen-bond interactions. In this paper, we describe 1 H-NMR studies carried out at room temperature on bi-and polyfunctionalized amines, namely: N-(3-amino-1-propyl)morpholine (3-APMo), histamine, 2-guanidinobenzimidazole (2-GB), 1,2-diaminoethane (EDA), 3-dimethylamino-l-propylamine (DMPA), and 1-(2-aminoethyl)piperidine (2-AEPip). By 1 H-NMR measurements of amine solutions at variable concentrations we have shown that 3-APMo, histamine and 2-GB are able to form a six-membered ring by intramolecular hydrogen bonding, while EDA, DMPA, and 2-AEPip form dimers by intermolecular hydrogen bonds. Likewise, variable concentration 1 H-NMR studies allowed estimation of the corresponding equilibrium constants for the dimerization. These results are correlated with experimental kinetic results of ANS, confirming hereto the relevance of the ''dimer mechanism'' in reactions involving these amines.

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Palabras clave: biorremediación, petróleo, explotación, biosólidos, suelos norpatagónicos, microorganismos nativos RESUMEN Las técnicas recientes de evaluación de sitios contaminados con hidrocarburos se fundamentan en la metodología del análisis de riesgo. El efecto sobre la salud y el ecosistema que producen agentes químicos presentes en un ambiente contaminado es estimado como la sumatoria de riesgos individuales, siendo la concentración de hidrocarburos un dato relevante. La biorremediación es una tecnología sustentable que acelera la degradación del petróleo en suelos contaminados y posee una relación costo beneficio favorable frente a otros métodos de remediación. El presente trabajo, realizado a escala de laboratorio, estudia la velocidad de degradación de distintas fracciones del petróleo mediante la incorporación de biosólidos (lodos cloacales) a un suelo contaminado de la Norpatagonia Argentina. Se determinó la concentración de hidrocarburos totales y el recuento de microorganismos presentes en el suelo al iniciar y finalizar el proceso de biorremediación. La degradación de las fracciones de hidrocarburos se analizó a intervalos regulares del proceso. Los resultados obtenidos mostraron una marcada disminución en la concentración de alcanos e hidrocarburos aromáticos de menor peso molecular a los 14 días de tratamiento. Los hidrocarburos de fracción pesada, resistentes a la biodegradación, mostraron reducciones significativas durante todo el proceso; su baja volatilidad y escasa migración por lixiviación indicarían que la degradación se debió principalmente al metabolismo de los microorganismos nativos presentes en suelos norpatagónicos. La comparación con el tratamiento convencional indica que la adición de biosólidos mejoró la remediación y que la biodiversidad de microorganismos presentes en el suelo es un factor importante para lograr una degradación significativa de fracciones del petróleo.