Síntese de 2-iodobenzamidas e 3-(iodoacetamido)benzamidas ligadas à D-galactose e suas reações de carbociclização radicalar mediadas por hidreto de tri-n-butilestanho

Starting from methyl 6-O-allyl-4-azido-2,3-di-O-benzyl-4-deoxy-α-D-galactopyranoside, four new derivatives containing 2-iodobenzamido and 3-(iodoacetamido)benzamido groups were synthesized. These four compounds were submitted to tri-n-butyltin hydride mediated radical cyclization reactions, resulting in two macrolactams from 11- and 15-endo aryl radical cyclization. The corresponding four hydrogenolysis products were also obtained. The structures of the new compounds were elucidated by ¹H and 13C NMR spectroscopy, DEPT, COSY, HMQC and HMBC experiments.

O ressurgimento da química de benzino com sililaril triflatos no contexto das reações de inserção em ligações sigma

In this paper we gathered articles concerning insertion reactions of arynes, exclusively generated from 2-(trimethylsilyl)aryl triflates in the presence of fluoride ions, in substrates bearing nucleophilic and electrophilic portions separated by sigma bonds. Accordingly, we stand out the great importance and versatility of such transformations in the preparation of highly functionalized aromatic systems, which are hardly synthesized in just one step for other methods.

Dificuldades conceituais no aprendizado de equilíbrios químicos envolvendo reações ácido-base

Common student misunderstandings regarding chemical equilibrium are reported taking into account the response of freshman students to some typical questions involving acid-base reactions. Language has been shown to be one of the main issues associated with students' difficulties on this subject, such as in the case of concentration and amount of substance (mol). Another usual problem was observed in questions involving buffer solutions after addition of a reagent. A number of recommendations have emerged from the results presented in this work as an attempt to enhance the learning of this topic in general chemistry courses given to first-year students.

Avaliação da natureza da atividade catalítica de compostos de bismuto em reações de metanólise do óleo de soja

Sodium bismuthate dihydrate and two species derived from its thermal treatment were investigated as catalysts for soybean oil methanolysis and, regardless of the type of solid used, ester yields always above 76 wt% were obtained. After a single reaction course, both liquid and solid phases were characterized using several analytical methods such as X-ray diffraction and thermogravimetric analysis. As a result, the catalytic phenomenon was shown to be solely due to the leaching of alkalinecatalytic species from the solid materials.

Reações multicomponentes de Biginelli e de Mannich nas aulas de química orgânica experimental: uma abordagem didática de conceitos da química verde

The introduction of Mannich and Biginelli multicomponent reactions in a practical Organic Chemistry course is presented in this article. Procedures described in the literature were adapted for use under the simple conditions available in undergraduate laboratories and were selected on the basis of Green Chemistry principles and practicality of synthesis. The reactions are easy to carry out and all products are readily isolated as crystalline solids with yields ranging from moderate to high.

Montmorilonita modificada como catalisador heterogêneo em reações de esterificação (m)etílica de ácido láurico

ABSTRACT Montmorillonite was modified with zirconium polyoxycations in the presence of ammonium sulphate. The material was characterized and used as a catalyst in the esterification of lauric acid, the reactions being accompanied by 2³ factorial design. Conversions of up to 95.33 and 83.35% were observed for the methyl and ethyl esterification reactions respectively, proving superior to results obtained by thermal conversion. The material was submitted to three reaction cycles and similar conversions were observed, indicating the catalyst is not significantly deactivated after reuse. The catalyst was also tested under reflux conditions, yielding a maximum conversion of 36.86%.

Novas métricas holísticas para avaliação da verdura de reações de síntese em laboratório

New semi-quantitative metrics for simple evaluation of global greenness of chemical reactions used in teaching laboratories, namely, the Green Circle (GC) and Green Matrix (GM), were developed. These metrics globally consider all Twelve Principles of Green Chemistry. To illustrate their construction, the greenness of several syntheses performed in the laboratory under different sets of conditions was assessed. The tools were validated by comparing the results with another metric, the Green Star (GS), developed in our previous study. Results showed these new metrics were useful for the intended purpose, having the advantage of being simpler than the GS.

Reações ácido-base: conceito, representação e generalização a partir das energias envolvidas nas transformações

Undergraduate students on the first year of Chemistry Courses are unfamiliar with the representation of acid-base reactions using the ionic equation H+ + OH- → H2O. A chemistry class was proposed about acid-base reactions using theory and experimental evaluation of neutralization heat to discuss the energy involved when water is formed from H+ and OH- ions. The experiment is suggested using different strong acids and strong base pairs. The presentation of the theme within a chemistry class for high school teachers increased the number of individuals that saw the acid-base reaction from this perspective.

Estudo do comportamento da lipase comercial Lipozyme RM IM em reações de esterificação para obtenção de biodiesel

The aim of this work was to study monoalkyl ester synthesis catalyzed by immobilized lipase Lipozyme RM IM via the esterification reaction. Yields of over 90% were obtained with butanol in esterification reactions with oleic acid. In the reactions with deodorizer distillates of vegetable oils and butanol, the conversion obtained was greater than 80% after 2.5 h. For the esterification reaction of palm fatty acid deodorizer distillate (PFAD) and butanol, seven reuse cycles of Lipozyme RM IM were carried out and the final conversion was 42% lower than the initial conversion.

Estudo de reações químicas homogêneas via método de Monte Carlo

By using the Monte Carlo simulation platform with probabilistic mathematical functions of the Boltzmann type, , having activation energy and temperature as parameters, it was possible to assess important dynamic aspects of homogeneous chemical reactions of the types A → B and A B. The protocol proved a useful tool in work with the basic concepts of Kinetics and Thermodynamics allowing its application both in class activities and for assisting experimental procedures.

Contextualizando reações ácido-base de acordo com a teoria protônica de Brönsted-Lowry usando comprimidos de propranolol e nimesulida

This paper reports the use of alternative materials for teaching experimental chemistry. In this context, nimesulide and propranolol tablets were used to teach chemical concepts about acid-base reactions according to Brönsted-Lowry protonic Theory. Important topics of Organic, Analytical and Pharmaceutical Chemistry were discussed, such as purification by acid-base extraction, solubility of organic compounds in aqueous solutions, buffers, the dissociation constant (pKa), potentiometric titration and ionization of drugs in biological fluids. The purification of propranolol and nimesulide from tablets produced yields of 75% and 90%, respectively. The experimental values of pKa for both drugs were in agreement with those from the literature.

Modificação e caracterização do resíduo pó de aciaria elétrica (PAE) para aplicação em reações de redução de cromo (VI)

In this study, electric arc furnace dust (EAFD) was thermally modified at different temperatures under H2 flow or charcoal in order to obtain reduced iron phases (Fe3O4, FeO and Fe0). The formation of these phases was confirmed by powder X-ray diffraction. The tests performed for reducing Cr (VI) using resultant materials obtained after thermal treatment of the EAFD showed excellent results, with PAE600H (EAFD reduced at 600 ºC under H2 flow) decreasing around 100% of the Cr (VI) in only 10 minutes of reaction. These results indicate the possibility of adding value to the residue, obtaining materials that offer great potential for environmental applications.

A Importância da determinação analítica de intermediários reativos e de seus produtos de reações com biomacromoléculas: uma mini revisão

Metabolic reactive intermediates can react with biomolecules such as DNA and proteins to produce adducts. Recently, research has shown that such adducts can act as precursors of some chronic diseases (cancer, Parkinson's, immunologic system diseases, etc.), and their determination is important because they are biomarkers of undesirable health effects. These compounds are produced at very low concentrations, but the development and dissemination of sensitive new analytical tools, especially those based on chromatography coupled to other analytical instruments, make such determinations possible. This mini review is focused on the formation of reactive intermediates, their reaction with biomolecules, and the importance of their determination.

Produção de lipases de Aspergillus niger e Aspergillus fumigatus através de fermentação em estado sólido, avaliação da especificidade do substrato e seu uso em reações de esterificação e alcoólise: evaluation of substrate specificity and use in esterification and alcoholysis reactions

Filamentous fungi were cultured under solid state fermentation of soybean residues to produce lipases. Enzymes produced by Aspergillus niger esterified oleic and butyric acids in the presence of ethanol, while enzymes produced by Aspergillus fumigatus demonstrated no esterification activity toward lauric acid. In case of A. niger, direct lyophilization of fermented bran led to higher esterification activity. The esterification of oleic acid by enzymes of A. fumigatus was neither influenced by pH adjustment nor by the extraction process. Conversions to ethyl esters were higher after pH adjustment with lyophilized liquid extract of A. niger.

Bateria de métricas para avaliação da verdura material de reações de síntese

The use of a battery of three mass metrics (atomic economy - AE, reaction mass efficiency - RME, and mass intensity - MI) for systemic evaluation of the material greenness of synthesis reactions is presented. Material greenness is discussed in terms of materialization/dematerialization of the reaction system and also according to the first two Principles of Green Chemistry, and is shown to involve two components: atomic greenness (incorporation of the atoms provided by reagents into the product, evaluated by AE and RME); and massic greenness (global mass of reagents and non-stoichiometric materials, evaluated by MI, related to the production of residues).