Otimização da reação de interesterificação química do óleo de palma

The Brazilian market has been showing a growing concern with nutritional values of oil components of foods. Chemical interesterification is a promising alternative to the current processes of modifying the consistency of oils. Chemical interesterification of deodorized palm oil was studied on a laboratory scale. The best results were obtained with 0.4% MeONa and heating for 20 min at 100 °C. These conditions are based on the largest variation in triacylglycerols as compared to a control. The trisaturated values varied from 6.2 to 9.9%, showing that the consistency of the oil improved for it to be used in margarines, without the formation of trans isomers.

A reação de metátese de olefinas: reorganização e ciclização de compostos orgânicos

The olefin metathesis reaction allows the exchange of complex alkyl units between two olefins, with the formation of a new olefinic link and a sub-product olefin usually ethylene. This reaction has found extensive application in the last ten years with the development of the Grubbs and Schrock catalysts, in total synthesis of complex organic molecules, as opposed to the very important use in the petrochemical industry with relatively simple molecules. This review intends to trace a historical and mechanistic pathway from industry to academy, before illustrating the more recent advances.

Parâmetros termodinâmicos da reação de adsorção de boro em solos tropicais altamente intemperizados

The driving force of boron adsorption on some tropical soils was evaluated by means of thermodynamic parameters. The batch method was employed, and the reaction was monitored at different pH values. The Langmuir equation successfully fitted the experimental results and provided reasonable isotherm parameters. Boron adsorption increased as a function of the pH of the soil solution and the concentration of added boron. The reaction was favorable and proceeded spontaneously, being strongly exoergic, as indicated by a negative free energy (deltaG) and a separation factor (K R) < 1. The boron adsorption phenomenon and the soil-solution interface were thermodinamically described using a theoretical model.

Síntese de aliloxi-orto-iodobenzamida derivada de d-glicose e reação de ciclização radicalar mediada por hidreto de tri-n-butilestanho

Methyl 6-O-allyl-2,3-di-O-benzyl-4-deoxy-4-(2 -iodobenzoylamine)-alpha-D-glucopyranoside was synthesized in nine conventional steps from methyl alpha-D-glucopyranoside. Its Bu3SnH-mediated aryl radical cyclization provided a benzomacrolactam, resulting from 11-endo aryl radical cyclization and the reduced uncyclized product methyl 6-O-allyl-4-benzoylamine-2,3-di-O-benzyl-4-deoxy- alpha-D-glucopyranoside. The structures of the three new products were supported by ¹H and 13C NMR spectroscopy and DEPT, COSY and HMQC experiments.

A reação de ciclização de prins: uma estratégia eficiente para síntese estereosseletiva de anéis tetraidropirânicos substituídos

The Prins cyclization reaction has significantly advanced in the last years as demonstrated by a number of applications described in the literature. The objective of this report is to introduce this powerful synthetic methodology to the undergraduate and graduated student, since it is rarely presented in an organic synthesis formal course. This reaction is, in some cases, the methodology of choice for the preparation of natural products or drugs that present the tetrahydropyrane moiety in their structures. In this report we show some aspects of this reaction, including mechanism, scope and limitations.

Efeito dos ácidos hexenurônicos e da lignina no desempenho da ozonólize, em diferentes pHs da reação

The effect of pH on the performance of the ozonolysis stage in pulp production was evaluated for conventional and acid treated brown and oxygen delignified eucalyptus kraft pulps. The objective was to determine separately the effects of lignin and hexenuronic acid on the performance of the ozonolysis stage. The reaction of ozone with hexenuronic acid is less sensitive to pH than the reaction of ozone with lignin. The efficiency and the selectivity of the reaction of ozone with pulp decreases after removal of hexenuronic acids. Increasing up to 7.0 the pH during the ozonolysis is viable in the sequence Z/D(EOP)D, resulting in savings of H2SO4 (8,5 kg/tsa) and NaOH (5 kg/tsa), but is not recommended in the sequence Z/ED(PO).

Influência da temperatura do ar de secagem sobre o teor e a composição química do óleo essencial de Lippia alba (Mill) N. E. Brown

Leaves of Lippia alba were submitted to six different drying treatments, using air at ambient temperature and heated up to 80 °C. The essential oil was extracted by steam distillation and analyzed by GC-MS. For the dried leaves, the oil content was reduced by 12 to 17% when compared with the fresh plant (0.66%). The major oil component was citral, representing 76% for the fresh plant, and varying from 82 to 84% for the dried material. These results showed that L. alba can be submitted to a drying process of up to 80 ºC without degradation and/or loss of the major, [LC1] active component.

Estudo termogravimétrico do efeito da temperatura e da atmosfera na absorção de dióxido de enxofre por calcário

Thermogravimetry was applied to investigate the effects of temperature and atmosphere on conversion of sulfur dioxide (SO2) absorbed by limestone. Ranges of temperature and particle size were studied, typical of fluidized-bed coal combustion. Isothermal experiments were performed at different temperatures (between 750 and 950 ºC) under local atmospheric pressure (~ 697 mmHg) in dynamic atmospheres of air and nitrogen. The maximum conversion was 29% higher in nitrogen atmosphere than in air atmosphere. The optimum conversion temperature was found at 831 ºC in air atmosphere and at 894 ºC in nitrogen atmosphere.

Avaliação da reação foto-fenton na decomposição de resíduos de carrapaticida

Experimental procedures based on factorial design and surface response methodology were applied to establishe experimental conditions for the decomposition of a 1:400 (v/v) Supocade® (chlorfenvinphos 13.8% and cypermethrin 2.6%) solution, used to control cattle ticks. Experiments exploring photo-oxidative reactions were performed with and without UV radiation, fixing exposition time and pesticide volume, and varying the oxidant mixture. The use of 3.6 mmol L-1 Fe2+ plus 1.9 mol L-1 H2O2 plus UV radiation provided destruction of 94% of the original carbon content and reduction of aromatic, aliphatic and carbinolic compounds, evaluated by determination of residual carbon content by ICP OES and NMR analysis.

Otimização e validação da técnica de extração líquido-líquido com partição em baixa temperatura (ELL-PBT) para piretróides em água e análise por CG

The liquid-liquid extraction with the low temperature partition technique was developed for the analysis of four pyrethroids in water by CG. Using a factorial design the extraction technique was optimised evaluating the effect of the variables ionic strength, contact time and proportion between sample and solvent volumes. The validation parameters sensitivity, precision, accuracy and detection and quantification limits were evaluated. The LOD and LOQ of the method varied from 1.1 to 3.2 µg L-1 and 2.7 to 9.5 µg L-1, respectively.

Mecanismo e aplicações da reação de fenton assistida por compostos fenólicos redutores de ferro

The mechanism and applications of the Fenton reaction assisted by iron-reducing phenolic compounds (IRPC) is reviewed. The presence of IRPC leads to the formation of a larger number of free radicals. The relationship between the redox potential and the IRPC structure is discussed. The effect of humic substances in the degradation of xenobiotics is also included, since these substances are able to reduce metallic ions. The natural occurrence of Fe3+/H2O2/IRPC in wood biodegradation processes, as well as their application is also discussed. The review concludes with the advantages of the Fe3+/H2O2/IRPC systems and some considerations for further process optimization and their applications at industrial levels.

Estudo do efeito de tratamentos térmicos em catalisadores de PtRu/C frente à reação de oxidação de hidrogênio na presença de CO

In this work the effects of time and temperature of thermal treatments under reducing atmosphere (H2) on PtRu/C catalysts for the hydrogen oxidation reaction (HOR) in the presence of CO on a proton exchange membrane fuel cell (PEMFC) single cells have been studied. It can be seen that the increase of the treatment temperature leads to an increasing sintering of the catalyst particles with reduction of the active area, although the catalyst treated at 550 ºC presents more CO tolerance for the HOR.

Determinação dos parâmetros de arrhenius da reação de sorção do dióxido de enxofre por calcário

Sulfur emission in coal power generation is a matter of great environmental concern and limestone sorbents are widely used for reducing such emissions. Thermogravimetry was applied to determine the effects of the type of limestone (calcite and dolomite), particle size (530 and 650 µm) and atmosphere (air and nitrogen) on the kinetics of SO2 sorption by limestone. Isothermal experiments were performed for different temperatures (650 to 950 ºC), at local atmospheric pressure. The apparent activation energies, as indicated by the slope of the Arrhenius plot, resulted between 3.03 and 4.45 kJ mol-1 for the calcite, and 11.24 kJ mol-1 for the dolomite.

Biodiesel de soja: reação de transesterificação para aulas práticas de química orgânica

The transesterification procedure of triacylglycerides from soybean oil (in natura and waste oil) to give biodiesel was adapted to semi-micro laboratory scale as an additional experimental technique of nucleophilic acyl substitution for undergraduate courses in Chemistry and related areas.

Influência de M/C (M = Mo, Cu, Fe e W) incorporado à camada difusora do eletrodo de difusão de gás frente à reação de oxidação de hidrogênio na presença de CO

The performance of proton exchange membrane fuel cells (PEMFC) with Pt-based anodes is drastically lowered when CO-containing hydrogen is used to feed the system, because of the strong adsorption of CO on platinum. In the present work the effects of the presence of a conversion layer of CO to CO2 composed by several M/C materials (where M = Mo, Cu, Fe and W) in gas diffusion anodes formed by Pt catalysts were investigated. The diffusion layers formed by Mo/C e W/C show good CO-tolerance, and this was attributed to the CO removal by parallel occurrence of the water-gas shift reaction and the so-called bifunctional mechanism.