Validação de método para a determinação de 5-hidroximetilfurfural em mel por cromatografia líquida e sua influência na qualidade do produto

In honey 5-hydroxymethyl-2-furaldehyde (HMF) is one of the most typical products of degradation: it is usually absent in fresh honey, but its concentration tends to rise as a result of heating processes or long-term storage. The validation protocol was performed in terms of detection and quantification limits, precision (by repeatability and intermediate precision), linearity and accuracy (by recovery tests). The method has been tested on 15 honey samples of different ages and geographical origin. HMF correlated highly with the age of the samples has been considered a very important parameter to put these honeys on the market or not and/or to estimate their shelf life.

Esterificação de ácidos graxos utilizando zircônia sulfatada e compósitos carvão ativado/zircônia sulfatada como catalisadores

In this work sulfated zirconia (SZr) and activated carbon/SZr composites produced by impregnation method with or without heating treatment step (CABC/SZr-I and CABC/SZr-I SC) and by the method of synthesis of SZr on the carbon (CABC/SZr-S) was used as catalysts in the esterification reactions of fatty acids. The SZr presented very active, conversions higher than 90% were obtained after 2 h of reaction. The activity of the composite CABC/SZr-I20%SC was up to 92%, however, this was directly related to time and temperature reactions. CABC/SZr-I and CABC/SZr-S were less active in esterification reactions, what could be attributed to its low acidity

Efeitos da história térmica nas propriedades do polímero pet: um experimento para ensino de análise térmica

Polyethilenetherephtalate (PET) is commonly used in manufacturing of beverage bottles representing a didactic appeal in thermal analysis education due to its presence in the student's day life. Additionally such polymer presents well defined thermal analytical curves and a well known thermal behavior. TGA curve is used to present the thermal stability. The thermal history effects in the thermal properties of a PET sample from a soft drink bottle are used to demonstrate the effect of different heating/cooling conditions on glass transition, melting, crystallization and crystalline degree using DSC curves.

Desenvolvimento de microcélula eletroquímica para estudos de microrregiões

The construction and optimization of a device that can be applied to electrochemical studies in flat micro regions are described. This was developed as an attempt to study small regions of metallic samples, whose properties may differ completely from its macroscopic behavior and for studies in highly resistive medium. Some results were obtained for individual grains of polycrystalline samples, welded regions, pure copper, platinum, glassy carbon, single crystals of Cu-Zn-Al alloy, and steel in biodiesel without electrolyte intentionally added. The device showed to be useful for the proposed purpose, allowing to be automated and has potential possibilities of other applications.

Evaluation of pesticide adsorption in gas chromatographic injector and column

Components in complex matrices can cause variations in chromatographic response during analysis of pesticides by gas chromatography. These variations are related to the competition between analytes and matrix components for adsorption sites in the chromatographic system. The capacity of the pesticides chlorpyrifos and deltamethrin to be adsorbed in the injector and chromatographic column was evaluated by constructing three isotherms and changing the column heating rate to 10 and 30 ºC min-1. By using ANCOVA to compare the slope of calibration graphs, results showed that the higher the injector temperature (310 ºC) the lower the pesticide adsorption. Also, deltamethrin influenced the adsorption of chlorpyrifos on the column chromatographic.

Síntese da fenitoína assistida por micro-ondas: proposta de aula prática para alunos de graduação

Microwave synthesis is considered a breakthrough in the field of chemistry due to its benefits over conventional heating methods. We describe, for the first time, the total synthesis of phenytoin adapted for a microwave reactor, proposed as an experiment for undergraduate courses. When carried out with microwaves, the synthetic route provided phenytoin in 6 min and 30 s, while for conventional heating the total time was 170 min. The experiment also involves rapid identification of compounds by TLC, ¹H NMR, FT-IR and melting points determination.

Síntese e hidrólise de azalactonas de Erlenmeyer-Plöchl mediadas por radiação micro-ondas em aparelhos doméstico e dedicado: experimentos de química orgânica para a graduação

This work describes a green chemistry experiment for the synthesis of Erlenmeyer-Plöchl azalactones mediated by microwave irradiation, employing both dedicated and domestic equipment. Hippuric acid was reacted with equimolar amounts of benzaldehyde, p-chloro-benzaldehyde or p-N,N-dimethyl-benzaldehyde in acetic anhydride as the solvent. Acid hydrolysis of obtained 4-benzylidene-2-phenyloxazol-5(4H)-one under microwave and convectional heating afforded Z-α-(benzoylamino)cinnamic acid at a 51-61.5% yield. The UV-Vis molecular spectra of 4-benzylidene-2-phenyloxazol-5(4H)-one and 4-(4'-N,N-dimethylbenzylidene)-2-phenyloxazol-5(4H)-one were obtained in ethanol, CH2Cl2 and DMSO and bathochromic shift was observed for the latter azalactone.

Cat's claw oxindole alkaloid isomerization induced by common extraction methods

Cat's claw oxindole alkaloids are prone to isomerization in aqueous solution. However, studies on their behavior in extraction processes are scarce. This paper addressed the issue by considering five commonly used extraction processes. Unlike dynamic maceration (DM) and ultrasound-assisted extraction, substantial isomerization was induced by static maceration, turbo-extraction and reflux extraction. After heating under reflux in DM, the kinetic order of isomerization was established and equations were fitted successfully using a four-parameter Weibull model (R² > 0.999). Different isomerization rates and equilibrium constants were verified, revealing a possible matrix effect on alkaloid isomerization.

Use of heterogeneous catalysts in methylic biodiesel production induced by microwave irradiation

The effect of different heterogeneous catalysts on the microwave-assisted transesterification of sunflower oil for the production of methylic biodiesel in a monomode microwave reactor is described. The experiments were carried out at 70 ºC with a 16:1 methanolsunflower oil molar ratio and different heterogeneous basic and acidic catalysts. The results showed that the microwave-heated reactions occur up to four times faster than those carried out with conventional heating. The reactions were performed with 24 catalysts; pure calcium oxide (CaO) and potassium carbonate, either pure or supported by alumina (K2CO3/Al2O3), were the most efficient catalysts.

Simple, mild, and highly efficient synthesis of 2-substituted benzimidazoles and bis-benzimidazoles

A new convenient method for preparation of 2-substituted benzimidazoles and bis-benzimidazoles is presented. In this method, o-phenylenediamines were condensed with bisulfite adducts of various aldehydes and di-aldehydes under neat conditions by microwave heating. The results were also compared with results of synthesis by conventional heating under reflux. Structures of the products were confirmed by infrared, ¹H- and 13C-NMR spectroscopy. Short reaction times, good yields, easy purification of products, and mild reaction conditions are the main advantages of this method.

CARACTERIZAÇÃO E ATIVIDADE CATALÍTICA DE K2CO3/AL2O3 NA TRANSESTERIFICAÇÃO DO ÓLEO DE GIRASSOL COM AQUECIMENTO CONVENCIONAL E MICRO-ONDAS

Commercial and synthetic mesoporous aluminas impregnated with potassium carbonate were characterized by X-ray diffraction (XRD), nitrogen physisorption, infrared spectroscopy and 27Al MAS NMR. The activities in the transesterification reaction of sunflower oil with methanol for biodiesel production were evaluated. 27Al MAS NMR spectra evidenced the presence of AlIV and AlVI in the samples, and also of AlV sites in the mesoporous synthesized alumina, which disappeared after impregnation with potassium salt followed by calcination. All aluminas containing potassium were active for biodiesel production from sunflower seed oil, with high conversions by both conventional heating and microwave irradiation.

DETERMINAÇÃO DE Cd E Pb EM AMOSTRAS DE GOMA XANTANA POR GF AAS

This paper describes the evaluation of a method for determination of Cd and Pb in xanthan gum samples by Graphite Furnace Atomic Absorption Spectrometry (GF AAS) using NH4H2PO4 as the chemical modifier. The sample preparation was performed using a reflux system adapted in the digestion tubes. With this system it was possible to increase the temperature of the digester block above the boiling point of the reaction medium, preventing loss of analyte and excessive evaporation of acids during heating. Samples were digested with HNO3 for 3 h in a digester block at 220 ºC. The limits of detection for Cd and Pb were 2.2 and 33.8 ng g-1, respectively. The RSDs for both analytes were, on average, lower than 5.0% and accuracy was verified by recovery tests, yielding values in the 83-100% range.

EXTRAÇÃO DE POLI(3-HIDROXIBUTIRATO), PRODUZIDO POR Cupriavidus necator, COM CARBONATO DE PROPILENO

The environmental impact of plastic waste has attracted worldwide attention. Amid the current context of increasing concern for the environment, biodegradable plastics have been widely studied as a replacement for synthetic plastics. Poly(3-hydroxybutyrate) (P(3HB)) is a biopolymer stored as an intracellular energy and reserve source in many microorganisms. Because it is an intracellular product, P(3HB) must be extracted from the cells at the end of the culture. The purpose of this study was to investigate the effect of extraction time, heating temperature, first standing time (after filtration and extraction), second standing time (after P(3HB) precipitation) and solvent amount, during the process of extracting P(3HB) from Cupriavidus necator DSM 545, using propylene carbonate as solvent. The extraction kinetic of P(3HB) with propylene carbonate from thermally treated biomass was evaluated at different temperatures. The physical properties of the P(3HB) obtained were also evaluated. In this case, P(3HB) obtained at optimal conditions of recovery (98%) and purity (99%) was used. Results showed that temperature was the most important factor in these responses for the range of values studied (110-150 ºC).

MICROWAVE ACTIVATION OF IMMOBILIZED LIPASE FOR TRANSESTERIFICATION OF VEGETABLE OILS

This work investigated the effect of microwave irradiation (MW) on the ethanolysis rate of soybean and sunflower oils catalyzed by supported Novozyme 435 (Candida antarctica). The effects of tert-butanol, water addition and oil:ethanol molar ratio on transesterification were evaluated under conventional heating (CH), and under optimum reaction conditions (with no added water in the system, 10% tert-butanol and 3:1 ethanol-to-oil molar ratio). The reactions were monitored up to 24 h to determine the conditions of initial reaction velocity. The investigated variables under MW (50 W) were: reaction time (5.0-180 min) and mode of reactor operation (fixed power, dynamic and cycles) in the absence and presence of tert-butanol (10% (w/w). The measured response was the reaction conversion in ethyl esters, which was linked to the enzyme catalytic activity. The results indicated that the use of microwave improved the activity at fixed power mode. A positive effect of the association of tert-butanol and MW irradiation on the catalytic activity was observed. The reaction rate improved in the order of approximately 1.5 fold compared to that under CH with soybean oil. Using soybean oil, the enzymatic transesterification under MW for conversion to FAEE (fatty acid ethyl esters) reached >99% in 3h, while with the use of CH the conversions were about 57% under similar conditions.

PARÂMETROS TERMODINÂMICOS DA CASCA DE LARANJA DESIDRATADA

The global energy scenario is currently a widely discussed topic, with growing concern about the future supplies. Thus, much attention has been dedicated to the utilization of biomass as an energy resource. In this respect, orange peel has become a material of great interest, especially to Brazil, which generates around 9.5 million tons of this waste per year. To this end, the authors studied the kinetics of the thermal processing of dried orange peel in inert and oxidizing atmosphere. The thermodynamic parameters were determined by the Ozawa-Flynn-Wall method for the global process observed during heating from the 25°C up to 800°C. The thermal analysis in air and nitrogen showed 3-2 stages of mass loss, respectively, with approximately 20% residual mass under a nitrogen atmosphere. The increase in the values of activation energy for the conversion points between 20% and 60% for thermal effects in air and nitrogen atmosphere was observed. The activation energy obtained in an oxidizing atmosphere was higher than that obtained under a nitrogen atmosphere. The fourier-transform infrared spectroscopy and X-ray diffraction analysis showed that the material has a high level of complexity with the presence of alkali and alkaline earth groups as well as phosphate, plus substances such as pectin, cellulose and lignin.