Cecilia E. Silvana Alvaro

Aggregation effects in the reactions of 2,4-dinitrochlorobenzene with aniline in aprotic solvents

The kinetics of the reaction of 2,4-dinitrochlorobenzene with aniline have been studied in toluene and in toluene–methanol binary solvents and compared with the reactions in benzene and chloroform. The reactions in aprotic solvents exhibit a rate dependence that is third-order in amine consistent with aggregates of the aniline acting as the nucleophile. Molecular complexes between the aniline and the substrate were also detected spectrophotometrically. Additionally, an inhibitory effect of toluene complexes was observed, which is similar to the previously reported effect of benzene in the reaction of the same substrate with n-butylamine. The reaction in the presence of pyridine shows an amine dependence which indicates formation of ‘mixed aggregates’ between aniline and pyridine. All the above results, as well as recently reported studies of other reactions different from SNAr, are fully interpreted within the ‘dimer nucleophile’ mechanism.

Pedagogic Proposal Focused on Sustainable Development: Fracking, a Matter of Active Debate at Present in the Argentine Patagonia

This research focuses on the development of a pedagogic unit on hydrocarbons for the last year of high school students that links the contents of science with social, technological and environmental aspects using a global approach (STES). This proposal emphasizes an holistic view of school contents, selecting a controversial topic such as oil extraction by hydraulic fracture known as “fracking” that arouses a deep debate due to its social implications. This exploratory research uses a qualitative methodology focused on a case study. Empirical evidence is gathered using classroom observations, student surveys and teachers´ interviews. Due to the size of the sample limited to a small group of students, this study does not admit generalizations, it only shows a tendency. This paper is a contribution to future research on STES approach in High School.

BIODEGRADACIÓN AEROBIA DE FRACCIONES DE HIDROCARBUROS PROVENIENTES DE LA ACTIVIDAD PETROLERA EN UN SUELO DE LA REGIÓN PATAGONIA NORTE, ARGENTINA

Recent techniques for assessing hydrocarbon contaminated sites are mainly based on risk analysis methodology. The effects of chemicals present in contaminated sites on the human health and the ecosystem are usually estimated as the addition of individual risks. In this sense, the hydrocarbon concentration is a relevant data. Bioremediation is a sustainable technology that accelerates the full or partial degradation of petroleum in contaminated soils and it shows a suitable cost-benefit ratio over other remediation methods. This work describes a laboratory scale study of the degradation rate for petroleum fractions by the incorporation of “biosolids” (sewage sludge) in an oil contaminated Patagonian soil. The determination of the total hydrocarbon concentration and the count of microorganisms in soil were performed both at the beginning and the end of the bioremediation process. The hydrocarbon degradation was analyzed at regular intervals during the study. The observed results showed that alkanes and lower molecular weight aromatic hydrocarbon concentrations were negligible after 14 days of treatment. The heavy hydrocarbon fraction, considered recalcitrant to biodegradation, was also significantly reduced during the biodegradation process. Since heavy hydrocarbons have low volatility and scarse migration by leaching, the observed decrease indicates that heavy hydrocarbon elimination could be mainly due to the native microorganism activity in the north Patagonian soils. Comparison with conventional treatment indicates that addition of “biosolids” enhances hydrocarbon remediation and that the biodiversity of microorganisms in soils is an important factor in achieving significant petroleum degradation.