Adaptação de forno de microondas doméstico para realização de reações de transesterificação sob refluxo e catálise por argilas

The microwave oven became an important source of heating for many laboratory procedures including accelerating organic reactions. Reactions that require long reflux times can sometimes be carried out in a few hours or minutes in a conventional microwave oven. However, longer reflux times can be troublesome since domestic microwave ovens are not prepared for these harsh conditions. This technical note presents our finding on heterogeneous catalysis transesterification reactions between b-keto-esters and carbohydrate derivatives under heating or microwave irradiation using an adapted domestic microwave oven.

Constituintes químicos de Galianthe brasiliensis (RUBIACEAE)

This paper describes the chemical constituents isolated from aerial parts of the plant Galianthe brasiliensis. From a methanol extract, the iridoid glycosides asperuloside, deacetylasperuloside, mixture of Z- and E-6-O-p-coumaroylscandoside methyl ester, the triterpene ursolic acid and the steroids stigmasterol, campesterol, beta-sitosterol and 3-O-beta-glycopiranosyl sitosterol were isolated. The structures of the natural products were identified on the basis of spectral data, including 2D NMR experiments. The antiproliferative properties of the crude methanolic extract were investigated against a series of nine human cancer cell lines.

Otimização das condições de produção de ésteres etílicos a partir de óleo de peixe com elevado teor de ácidos graxos ômega-3

The production of ethyl esters by alcoholysis is an alternative for splitting triacylglycerols due to the possibility of using low temperatures, which results in oxidative protection of the polyunsaturated fatty acids. Ethyl esters produced under mild conditions of temperature could be used as substrate for obtaining structured lipids. The reaction parameters of production of ethyl esters from fish oil with high content of omega-3 fatty acids by alcoholysis were optimized using response surface methodology. An experimental design (2³) (with levels +1 and -1, six axial points with levels -alpha and +alpha and three central points) was applied. The variables investigated were concentration of catalyst, amount of ethyl alcohol and temperature. Ethyl ester conversion was monitored by high performance size exclusion chromatography (HPSEC) and the best result obtained was 95% conversion rate. The optimal conditions were 40 °C, 1% of NaOH and 36% of ethanol.

Principais métodos de síntese de amidinas

The amidine functional group is found in a wide range of natural products and is biologically active against several pathogens. In addition, amidines have long been regarded as useful intermediates in the synthesis of heterocyclic compounds. Consequently, a great number of methods have been developed for the preparation of amidines. Pinner's method is the most commonly used. Conventional methods include: - the addition of metal amides or amines to nitriles, the addition of amines to imido esters and the condensation of amides with amines in the presence of halogenating reagents. In this report, the main methods for synthesis of amidines will be described.

Constituintes químicos e avaliação do potencial alelopático de Adiantum tetraphyllum Humb. & Bonpl. Ex. Willd (Pteridaceae)

Chemical studies of green leaves of A. tetraphyllum afforded beta-sitosterol, a mixture containing the ethyl esters of long chain carboxylic acids, 30-normethyl-lupan-20-one, hopan-22-ol, phytol, phyten-3(20)-1,2-diol, quercetin and quercetin-3-O-beta-D-glucoside. The structures of the compounds were elucidated by spectroscopic and GC analysis. The allelopathic potentials of the crude ethanolic extract and fractions were evaluated against Lactuca sativa (letuce) and Allium cepa (onion) seeds.

Teores de carbamato de etila e outros componentes secundários em diferentes cachaças produzidas em três regiões do estado de Minas Gerais: Zona da mata, sul de minas e vale do jequitinhonha

Minas Gerais is the highest producer of handmade spirits. Research has been carried out aiming to contribute to progress. Thus, the goal of this work is to evaluate the quality of spirits in three different regions of Minas Gerais state. We analyzed ethyl carbamate, alcoholic grade, volatile acidity, higher alcohols, aldehyde, esters, methanol, furfural and copper. The values obtained for ethyl carbamate varied from undetectable to 643.5 µg L-1, with only one region not following the legislation (150 µg L-1). Most of the compounds in the spirits were present within the limits estabilished by the legislation.

Alternative technique for biodiesel quality control using an optical fiber long-period grating sensor

We report the use of an optical fiber sensor to measure the soybean oil concentration in samples obtained from the mixture of pure biodiesel and commercial soybean oil. The operation of the device is based on the long-period grating sensitivity to the surrounding medium refractive index, which leads to measurable modifications in the grating transmission spectrum. The proposed analysis method results in errors in the oil concentration of 0.4% and 2.6% for pure biodiesel and commercial soybean oil, respectively. Techniques of total glycerol, dynamic viscosity, density, and hydrogen nuclear magnetic resonance spectroscopy were also employed to validate the proposed method.

Novos constituintes químicos das cascas do caule de Tabebuia heptaphylla

A new triterpene, 3beta,6beta,21beta-trihydroxyolean-12-ene and a new iridoid, 8alpha-methyl-8beta-hydroxy-6beta-(3',4'-dimethoxy)benzoyloxy-1 alpha,3alpha-dimethoxy-octahydro-cyclopenta[c]pyran were isolated from the trunk bark of a specimen of Tabebuia heptaphylla (Bignoniaceae) collected in the "Pantanal" of Mato Grosso do Sul, Brazil. Twelve known compounds were also obtained in this work, comprising four iridoids, 6-O-p-hydroxybenzoylajugol, 6-O-p-methoxybenzoylajugol, 6-O-3",4"-dimethoxybenzoylajugol, 8alpha-methyl-8beta-hydroxy-6beta-(4'-hydroxy)benzoyloxy-1alpha,3 alpha-dimethoxy-octahydro-cyclopenta[c]pyran, a cyclopentene dialdehyde, 2-formyl-5-(3',4'-dimethoxybenzoyloxy)-3-methyl-2-cyclopentene-1-acetaldehyde, a phenylethanoid glycoside, verbascoside and three benzoic acid derivatives, p-hydroxybenzoic, p-methoxybenzoic and 3,4-dimethoxybenzoic acids, in addition to squalene, sitostenone and sitosterol. The antioxidant properties of the isolated compounds were also evaluated in this work.

Efeito da presença e concentração de compostos carbonílicos na qualidade de vinhos

Studies on identification of compounds that make up the aroma and flavor in wines involve research evaluating mainly the influence of terpenes, esters, lactones and alcohols upon these sensory characteristics. However, carbonylic compounds (CC) play an important role concerning the substances that impact aroma to these drinks. Their origin is reported to be linked to the grape's chemical composition, must fermentation or micro-oxidation occurring during storage in barrels. Some CCs, like E-ionone, E-damascenone, siryngaldehyde, can contribute a pleasant aroma and improve the wine quality whereas others are responsible for unpleasant characteristics (acetaldehyde, furfural, 5-hydroxy-methyl furfural, diacetil, E-non-2-enal, etc). A fraction of CCs present is associated with bisulfite ions in the form of hydroxyalkylsulfonic acids. Some of them are stable and play an important role in determining wine quality. The reaction involving the formation of this aduct commonly occurs with CCs of low molar mass, such as formaldehyde and acetaldehyde. The reaction involving CCs with more than three carbon atoms demands further studies.

Transesterificação de óleos vegetais: caracterização por cromatografia em camada delgada e densidade

We studied the transesterification of two vegetable oils: soybean and waste frying oil. The main problem of transesterification is related to the measurement of the ethyl ester content. In this work we used a quick analytical method for assessing the ethyl ester fraction of the purified fuel-grade transesterification products by applying a simple correlation with density. If the ester content is higher than 85% by weight the correlation allows the determination by a single density measurement. This method is suitable for control and determines the ethyl ester quickly and simply.

70º aniversário do biodiesel em 2007: evolução histórica e situação atual no brasil

Periodically, during petroleum shortages, vegetable oils and their derivatives have been proposed as alternatives to petroleum diesel fuel. Different approaches have been proposed, including the use of pure vegetable oils (or blends) or their derivatives. Indeed, the use of fatty-acid methyl or ethyl esters (usually known as "biodiesel") produced by alcoholysis of triacylglycerides or esterification of fatty acids was initially proposed in Belgium 70 years ago, when the first world patent was deposited. Recently, foreign dependence on diesel fuel and the petroleum crisis have increased the discussion in Brazil on starting to use alternatives to diesel fuel, being biodiesel the alternative of choice for a large petroleum diesel substitution program.

Constituintes químicos de licania tomentosa Benth. (Chrysobalanaceae)

This paper describes the chemical constituents isolated from leaves and fruits of Licania tomentosa Benth. The plant materials were successively extracted with hexane and methanol. From the extracts the following compounds were obtained: betulinic acid; licanolide, a new triterpene lactone; oleanolic acid, lupeol; palmitoleic and hexadecanoic acid; a mixture of stigmasterol and sitosterol; and a mixture of tormentic, ursolic and betulinic acid. The structures of the natural products were identified on the basis of spectral data.

Síntese de padrões cromatográficos e estabelecimento de método para dosagem da composição de ésteres de ácidos graxos presentes no biodiesel a partir do óleo de babaçu

Several alkyl esters were synthesized, purified, characterized by ¹H NMR and employed as standards for establishing chromatographic methods to monitor their formation in the synthesis of biodiesel. The efficiency of the chromatographic methods was confirmed with the products of enzymatic transesterification of babassu oil with different alcohols (C2 to C4), using Lipozyme as catalyst.

Determinação da matéria-prima utilizada na produção do biodiesel adicionado ao diesel mineral através de monitoramento seletivo de íons

The selective ion monitoring acquisition mode in mass spectrometry was applied to identify, in the diesel complex matrix, the raw materials (vegetable oil and alcohol) that originate biodiesel. Biodiesel samples obtained from babassu, castor, palm and soybean vegetable oils and pure fatty acid methyl and ethyl esters were used to develop this method, using specific fragments in mass spectrometry and the "window system" in gas chromatography. The commercial Brazilian B2 samples were found to be produced with soybean oil, transesterified with methanol.

Efeito do 1-metilciclopropeno sobre a emissão dos ésteres voláteis de bananas ao longo do amadurecimento

Fresh green bananas (Musa sp., subgroup Prata) were treated with a dose of only 90 ηg g-1 of 1-MCP for 13 hours and the evolution of the volatile compounds along the ripeness was studied. A method to quantify the emission of esters was developed by cryogenic headspace and gas chromatography. Esters of acetate, butyrate, isobutyrate and isovalerate were found as major compounds. The application of the 1-MCP for 13 hours delayed the appearance of the coloration 8 of the peel for 3 days and decreased quantitatively in about 46% the total production of esters in the banana until the 15° day of harvested.