The inhibitory action of three imine-chalcones on carbon steel corrosion in HCl was investigated by theoretical and experimental methods. Quantum descriptors were calculated at the conductor-like polarizable continuum model (CPCM)-Becke-3 Parameter-Lee-Yang-Parr (B3LYP)-D3/def2-TZVPP level allowing the prediction of efficiency inhibition ranking. Electrochemical techniques and mass loss experiments were employed to determine inhibition efficiencies and related experimental parameters. Scanning electron microscopy was employed for metal surface analysis. The N-[(1Z,2E)-1,3-diphenylprop-2-in-1-ylidene]-1-phenethylamine (IM-F) was pointed out as the most efficient inhibitor in this group, with 96% of corrosion inhibition. Moreover, theoretical results obtained from periodic calculations for the adsorption on the Fe(110) surface corroborated the highest efficacy of IM-F.

Oxidative stability parameters (OSP), acid value (AV), water content (W), and the metallic copper corrosion rate in biodiesels obtained from eight different vegetable oils were determined. Simple and multiple linear regression models were constructed to explain the influence of the OSP, AV and W variables on the corrosion rate. The corrosion rate was lower in biodiesel with less oxidative stability because, instead of reacting with copper, O2 reacted preferentially with the unsaturated fatty acid methyl esters (FAME) that could act as “sacrificial molecules” to protect the copper against corrosion. Therefore, the corrosion rate was strongly related to the FAME composition. The AV was an important parameter in the corrosion process because free acids react with passivating agents, increasing the corrosion rate. The predictive capacity of W for corrosion rate was statistically insignificant, although water condensed on a copper surface causes corrosion.

Biodiesel synthesis from soybean oil using methanol and alkaline catalysts occurs in the following two consecutive steps: dispersion of methanol in the oil and methanolysis. The effect of the alkaline catalysts NaOCH3, KOCH3, NaOH, and KOH in the dispersion step at 30-60 ºC and under mechanical stirring at 400 rpm was evaluated. The dispersion step accounts for 44.6-73.3% of the total synthesis time and was poorly favored compared to methanolysis due to the increase in temperature. The catalysts decreased the dispersion time, although most of them increased the methanol-oil interfacial tension. K-containing catalysts were more active than their Na analogues due to higher adsorption of K+ in the methanol-oil interface and the higher production of methyl esters (which act as emulsifying agents), which promote a more favorable interfacial tension. The alkaline cation effect was more significant in the dispersion step than in the methanolysis step.

4-Nonylphenol, a degradation product of ethoxylated alkylphenols, due to its harmful effects on the environment, has been banned in European Union countries, alongside their precursors. The guide on quality of drinking water from the United States Environmental Protection Agency (US EPA) recommends a maximum concentration of 28 µg L-1 for fresh water. In Brazil, there is no clear legislation containing values of maximum concentration of 4-nonylphenol. Due to this lack of regulation, a continuous monitoring is necessary for this pollutant in environmental samples. The occurrence of 4-nonylphenol (4-NP) in the surface waters of Guandu River in the state of Rio de Janeiro, Brazil, was studied by using solid-phase extraction and reversed phase liquid chromatography separation with UV detection. The analytical method satisfies these requirements, being able to detect and quantify 4-NP in a desired concentration range. Of the 19 samples analyzed, 4-nonylphenol was detected in 12, quantified in 2, showing concentration levels of 1.73 and 2.32 µg L-1 in Santa Cruz and Paracambi, respectively. This is the main hydrographic basin in the state of Rio de Janeiro, where water is collected for treatment and later distributed to most cities in the metropolitan region, including Rio de Janeiro City, and these results are therefore alarming.

ABSTRACT This paper aims to gather and discuss important information about nonylphenol, such as physical chemistry properties, toxicity and analytical methods in various matrices. As a degradation product of ethoxylated alkylphenols, nonylphenol presents a higher degree of reactivity than its precursor. Due to its harmful effects on the environment, use and production of nonylphenol has been banned in European Union countries, alongside their precursors. The guide on quality of drinking water (USEPA) recommends a maximum concentration of 28 µg L-1 for fresh water. In Brazil, there is no clear legislation containing values of maximum concentration of nonylphenol. Due to this lack of regulation, a continuous monitoring is necessary of this pollutant in environmental samples. This paper aims to encourage further studies on nonylphenol, seen as a critical environmental pollutant. For proper monitoring is necessary to have reliable analytical methods and easy to perform in routine analysis.

The rate coefficient of the cis-3-hexene + Cl atoms reaction at 296 ± 2 K and 750 ± 10 Torr was determined using the relative rate technique. The reaction was investigated using an 80 L Teflon reaction bag and a gas chromatograph coupled with flame-ionization detection. Chlorine atoms were produced by the photolysis of trichloroacetyl chloride. No previous experimental data was available in the literature, to the best of our knowledge. The mean second-order rate coefficient value found was (4.13 ± 0.51) × 10-10 cm3 molecule-1 s-1. The experimental value agrees with the rate coefficient estimated by structure-reactivity analysis, 4.27 × 10-10 cm3 molecule-1 s-1. Moreover, both addition and hydrogen abstraction channels contribute to the global kinetics, with branching ratios 70:30. Effective lifetime with respect to Cl atoms is predicted as 67.2 hours; however, the cis-3-hexene + Cl channel is suggested to be non-negligible at atmospheric conditions. Other atmospheric implications are discussed.

Neste trabalho, o estudo teórico da reação de substituição nucleofílica de segunda ordem em fase gasosa, CH3Cl + OH-→ CH3OH + Cl-, é apresentado visando a descrição do caminho de reação e o cálculo de coeficientes de velocidade pelo método do estado de transição variacional canônico (CVTST). Cálculos teóricos foram conduzidos em nível MP2/6-31+G(d). A diferença de entalpia calculada para esta reação a 298,15 K (-49,93 kcal mol-1) está em bom acordo com o dado da literatura: -50,4 kcal mol-1. O coeficiente de velocidade calculado a 298,15 K, 1,94 × 10-9 cm³ molécula-1 s-1, também apresenta bom acordo com o dado experimental: 1,3-1,6 × 10-9 cm³ molécula-1 s-1. Além disso, os coeficientes de velocidade mostram comportamento não-Arrhenius, diminuindo com o aumento da temperatura, o que é consistente com a tendência experimental. Neste aspecto, a atuação da teoria de estado de transição variacional para essa reação deve ser considerada satisfatória.

In this work the theoretical study of the gas-phase bimolecular nucleophilic substitution reaction, CH3Cl + OH-→ CH3OH + Cl-, is introduced aiming the description of the reaction path and the calculation of rate coefficients with the canonical variational transition state (CVTST) method. The calculations were performed at the MP2/6-31+G(d) level. The calculated enthalpy difference for the reaction at 298.15 K (-49.93 kcal mol-1) is in good agreement with the literature value: -50.4 kcal mol-1. The calculated rate coefficient, 1.94 × 10-9 cm³ molecule-1 s-1 at 298.15 K, also shows good agreement with the experimental data: 1.3-1.6 × 10-9 cm³ molecule-1 s-1. Moreover, the rate coefficients show non-Arrhenius behavior, decreasing as the temperature increases, which is consistent with the experimental expectation. In this way, the performance of the variational transition state theory for this reaction can be considered satisfactory.

Neste trabalho, dados de poluentes legislados e não legislados foram obtidos em uma região industrial-residencial no Rio de Janeiro, no período de abril a novembro de 2002. As concentrações de formaldeído e acetaldeído encontradas estavam na faixa de 25,25-231,73 ppb e 9,48-75,74 ppb respectivamente. Estas altas concentrações podem ser atribuídas a diversas fontes: emissões veiculares e industriais, a presença de incineradores de lixo, efluentes e rejeitos despejados no rio Faria Timbó e emissões de uma industria de metanol. As concentrações médias de BTEX foram: 1,92, 9,02, 6,37, 21,65 e 5,99 µg m-3 para benzeno, tolueno, etilbenzeno, m,p-xileno e o-xileno, respectivamente. As concentrações médias de PM10 mostram valores máximos para o mês de outubro, abril e junho. As concentrações obtidas nas simulações foram para o mês de agosto usando um modelo de trajetórias. A concentração máxima de ozônio calculada foi de 39,8 ppb, as 15:00 horas, obtendo uma boa concordância com os dados experimentais (38,5 ppb). A isopleta de ozônio mostra que o local está em uma região alta de VOC/NOx, típica de áreas suburbanas e a favor do vento.

In this work, data for criteria and non-criteria pollutants were obtained in a suburban industrial-residential area in Rio de Janeiro, from April to November 2002. Formaldehyde and acetaldehyde concentrations were found in the ranges 25.25-231.73 ppb and 9.48-75.74 ppb, respectively. These high concentrations may be attributed to several sources: vehicular and industrial emissions, the presence of several trash incinerators, effluents and waste rejected in the Faria Timbó river and emissions from a methanol industry. Average BTEX concentrations were: 1.92, 9.02, 6.37, 21.65 and 5.99 µg m-3 for benzene, toluene, ethylbenzene, m,p-xylene and o-xylene, respectively. PM10 concentrations showed maximum mean values in October, April and June. Simulated concentrations were obtained for August 2002 using a trajectory model. The maximum calculated ozone concentration was 39.8 ppb, at 3:00 pm, in good agreement with experimental data (38.5 ppb). The ozone isopleths show that the local is in the high VOC/NOx region, typical of suburban and downwind areas.

Cálculos B3LYP usando bases até 6-311G(3d2f,3p2d) foram utilizados para a previsão acurada de propriedades termoquímicas relacionadas à reação de dissociação trans-HONO(X¹A') -> HO(X²P) + NO(X² P). Um estudo sistemático da influência da base foi realizado e resultados B3LYP foram comparados a dados experimentais e a outros resultados teóricos, calculados usando os métodos G2, G2MP2, CBS e métodos ab initio CCSD(T) e QCISD. Os resultados obtidos sugerem que para este tipo de processo unimolecular: cálculos B3LYP geram resultados mais acurados para entalpia de dissociação que outros métodos convencionais e o melhor acordo com dados experimentais foi obtido a partir de cálculos em nível B3LYP/6-311G(3d2f,3p2d): 49.2 kcal mol-1 (experimental) e 49.0 kcal mol-1 (calculado). Ainda, diferenças de entropia e de energia livre de Gibbs foram calculadas e constantes de equilíbrio foram determinadas segundo a expressão: Keq(T) = 1.16 × 10(28) × exp(-48.34/RT), para a faixa de temperatura 200 - 500 K.

B3LYP calculations using basis sets up to 6-311G(3d2f,3p2d) have been employed to predict accurate thermochemical properties related to the bond dissociation reaction trans-HONO(X¹A') -> HO(X²P) + NO(X² P). A systematic study of the influence of the basis set was performed and results were compared with experimental data and with other calculated results, obtained using standard Gaussian methods (G2 and G2MP2), complete basis set extrapolation methods (CBS) and ab initio calculations (CCSD(T) and QCISD). The results suggest that, for this kind of unimolecular process: B3LYP calculations produce bond dissociation enthalpies that are more accurate than standard ab initio methods and) the best agreement with the experimental enthalpy has been found with B3LYP/6-311G(3d2f,3p2d) calculations: 49.2 kcal mol-1 and 49.0 kcal mol-1, respectively. Also, entropy and Gibbs free energy have been calculated and equilibrium constants have been determined as Keq(T) = 1.16 × 10(28) × exp(-48.34/RT), for the temperature range 200 - 500 K.

A integração numérica das equações diferenciais ordinárias que descrevem um sistema cinético e a análise de sensibilidade dos resultados aos parâmetros são metodologias cada vez mais utilizadas na cinética química. Neste trabalho, é apresentado um estudo de simulação numérica da decomposição em fases gasosa de CF4 e de misturas CF4/O2 na presença de silício. É analisada a importância relativa dos processos individuais e são calculados os coeficientes de sensibilidade e o efeito da incerteza nos parâmetros. Os resultados são comparados com dados experimentais da literatura para ajustar os parâmetros do modelo. O principal agente de corrosão neste sistema é o flúor atômico. As concentrações das principais espécies (SiF4, CO, CO2 e COF2) dependem da composição da mistura.

Numerical integration of the coupled differential equations which describe a chemical reacting system and sensitivity analysis are becoming increasingly important tools in chemical kinetics. In this work, a numerical modelling analysis of the chemical processes in the gas-phase decomposition of pure CF4 and CF4/O2 mixtures, in the presence of silicon, was performed. The relative importance of individual processes was analysed and the sensitivity coefficients as well as the effect of the parameters uncertainties were determined . The results were compared with experimental data from the literature to adjust the model parameters. The main etching agent in the system is the fluorine atom. The concentrations of the main species (SiF4, CO, CO2 and COF2) depend on the composition of the mixture.

Neste trabalho é realizada a simulação numérica da decomposição em fase gasosa de SF6 e misturas de SF6/O2, na presença de silício. São determinadas as velocidades relativas dos processos individuais, o efeito da incerteza dos parâmetros e os coeficientes de sensibilidade. Os resultados são comparados com dados experimentais encontrados na literatura e resultados calculados previamente para a corrosão do silício, a fim de ajustar os parâmetros do modelo. À semelhança do que acontece com o CF4, o principal agente de corrosão é o flúor atômico e a concentração das principais espécies envolvidas depende da composição da mistura. A forma das curvas de sensibilidade segue o formato geral das curvas que representam a velocidade dos processos individuais e a relação entre os coeficientes de sensibilidade calculados para as diferentes etapas de reação é uma medida da contribuição de cada uma ao processo total.

In this work, a numerical modelling analysis of the gas-phase decomposition of pure SF6 and SF6/O2 mixtures, in the presence of silicon was performed. The relative rate of individual processes, the effect of the parameters uncertainties and the sensitivity coefficients were determined. The results were compared with literature experimental data for the plasma etching of silicon and with previous simulated results to adjust the model parameters. As in the CF4 system, the main etching agent is atomic fluorine and the concentration of the major species depends on the composition of the mixture. The shape of the sensitivity curves follows the general shape of the individual rate curves and the ratio between the calculated sensitivity coefficients is closely related to the contribution of each reaction.