Estudo experimental e teórico da redução de bases de Schiff derivadas da 3,3-difenilpropilamina

A series of seven Schiff bases have been synthesized from 3,3-diphenylpropilamine and substituted benzaldehydes. These imines were treated with NaBH4 in ethanol affording the corresponding amines in 98-55% yields. A molecular modeling study was performed with the Schiff bases in order to compare the theoretical parameters with the experimental results. The theoretical parameters were obtained by AM1 and PM3 semi-empirical methods. The analysis of charge, electron densities and LUMO coefficients suggested that the most favorable interactions should occur with Schiff bases containing electron-donating groups, in accordance with experimental yields, showing that the higher reactivity is due to higher electrophilic character of imine carbons.

Síntese de novos herbicidas derivados do 1,2alfa,4alfa,5-tetrametil-8-oxabiciclo[3.2.1]oct-6-en-3-ona

In this paper we report the synthesis of biologically active compounds through a [3+4] cycloaddition reaction to produce the main frame structure, followed by several conventional transformations. The 1,2alpha,4alpha,5-tetramethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one (11) obtained from a [3+4] cycloaddition reaction was converted into 1,2alpha,4alpha,5-tetramethyl-6,7-exo-isopropylidenedioxi-8 -oxabicyclo[3.2.1]octan-3-one (13) in 46% yield. This was further converted into the alcohols 1,2alpha,4alpha,5-tetramethyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (14), 1,2alpha,4alpha,5-tetramethyl-6,7-exo-isopropylidenedioxi-8 -oxabicyclo[3.2.1]octan-3beta-ol (15), 1,2alpha,4alpha,5-tetramethyl-3-butyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (17), 1,2alpha,4alpha,5-tetramethyl-3-hexyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (18) and 1,2alpha,4alpha,5-tetramethyl-3-decyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (19). Dehydration of 17, 18 and 19 with thionyl chloride in pyridine resulted in the alkenes 20, 21 and 22 in ca. 82% - 89% yields from starting alcohols. The herbicidal activity of the compounds synthesized was evaluated at a concentration of 100 µg g-1. The most active compound was 21 causing 42,7% inhibition against Cucumis sativus L.

Reciclagem química de zeólitas comerciais desativadas

Pyro and hydrometallurgical processes were applied to the treatment of spent commercial zeolites (a molecular sieve and a ZSM-5 sample). Both catalysts were employed in pilot plant units. They were kept in their original shape, they were not regenerated and were not subjected neither to mechanical stress nor to overheating zones during their time on-stream. Two recycling processes were tested: (i) direct solubilization of samples in mixtures of HF + H2O2 (60 ºC, 1 h). Although silicon was solubilized, insoluble matter was found in both samples, particularly in the molecular sieve, due to its high amounts of alkaline and alkaline-earth metals; (ii) fusion with KHSO4 (5 h, 600 ºC) with KHSO4/zeolite mass ratio 6:1. After fusion the solid was solubilized in water (100 ºC), leaving silicon as SiO2 residue. In both processes, solubilized metals were isolated by conventional selective precipitation techniques. Analysis of final products by common analytical methods shows that metals present in the original catalysts were recovered with very high yields except when the molecular sieve was treated with HF + H2O2. This reactant mixture proved to be suitable for processing zeolites with a low alkaline and alkaline-earth metal content whereas fusion with KHSO4 appeared to be adequate for all types of zeolites.

O uso do forno de microondas na síntese orgânica em fase sólida

Solid-phase organic synthesis (SPOS) has been considered the main strategy for the construction of combinatorial libraries, because its simplicity leads to faster synthetic procedures. In addition to that, a series of reports in the specialized literature show great advantages in the use of microwave activation, when compared to classical heating, for instance: shorter reaction times, in some cases from several hours to a few minutes, increase of selectivity and product yields, energy economy and reduction and/or elimination of solvent. This review describes the use of microwave ovens/reactors in solid phase organic synthesis, describing the advantages, equipment and reactions using both techniques.

Carbono do solo e a mitigação da mudança climática global

The soils of the world contain more carbon than the combined total amounts occurring in vegetation and the atmosphere. Hence soils are a major reservoir of carbon in terrestrial ecosystems and an important sink. Recently, emphasis has been placed on the need to sequester carbon from atmospheric carbon dioxide into soil organic matter because of international concerns about greenhouse gas emissions and global climate change. The best strategies to built-up carbon stocks in the soil are basically those that increase the input of organic matter to the soil, and/or decrease the rate of soil organic matter decomposition. Grain crop systems based on soil ploughing and harrowing lead to CO2 emissions combined with tremendous soil losses. In Brazil, no-tillage system was introduced to combat soil erosion by water and this soil management led to the build-up of soil carbon stocks with simultaneous high crop yields. However, the present procedure used to quantify carbon stocks in soils is laborious and of high cost. The use of infrared spectroscopy is very promising as an alternative low-cost method of soil carbon determination.

Síntese do monastrol e novos compostos de Biginelli promovida por In(OTf)3

In this paper, we describe a practical route for the synthesis of Biginelli compounds using In(OTf)3. To study the generality of this catalyst, several examples using aromatic aldehydes, 1,3-dicarbonyl compounds, urea, and thiourea were investigated. The present procedure provides an efficient modification of the classical Biginelli reaction, namely short reaction times and simple work-up, that not only preserves the simplicity of the original protocol but also produces excellent yields of 3,4-dihydropyridin-2(1H)-ones. Thiourea was used with similar success to provide the corresponding 3,4-dihydropyridin-2(1H)-thiones. In this case, the (+/-)-monastrol, antimitotic agent, was obtained in 92% yield and new thio analogues were synthesized.

Tiossemicarbazonas: métodos de obtenção, aplicações sintéticas e importância biológica

Thiosemicarbazones are a class of compounds known by their chemical and biological properties, such as antitumor, antibacterial, antiviral and antiprotozoal activity. Their ability to form chelates with metals has great importance in their biological activities. Their synthesis is very simple, versatile and clean, usually giving high yields. They are largely employed as intermediates, in the synthesis of others compounds. This article is a survey of some of these characteristics showing their great importance to organic and medicinal chemistry.

Quitosana: derivados hidrossolúveis, aplicações farmacêuticas e avanços

Chitin and chitosan are copolymers build from N-acetyl-D-glucosamine and D-glucosamine. The former is widely found in nature and yields the latter on deacetylation. The copolymers are being used for several purposes. Since 1977, when the First International Conference on Chitin and Chitosan was held in Boston, USA, the interest on chitin and chitosan has remarkably increased. This review emphasizes pharmaceutical applications of chitosan and its derivatives, and presents recent advances. Some therapeutical applications of these polymers are also discussed.

Recuperação de metais de catalisadores de hidrorrefino usados via fusão com KHSO4

This work describes a process for metal recovery from spent NiMo and CoMo/Al2O3 commercial hydrorefining catalysts. The samples were treated by fusion with potassium hydrogen sulfate (5 h, 600 ºC) with a KHSO4/catalyst mass ratio of 10:1. After fusion the solid was solubilized in water (100 ºC), leaving silicon compounds as residue. Losses of nickel and cobalt may reach 16 wt% of the amount present in the sample, depending on the silicon content. Soluble metals were isolated by selective precipitation techniques (nickel, cobalt, aluminum) or by solvent extraction with methyl-isobutyl ketone (molybdenum) in a hydrochloric acid medium. All metals were recovered in very good yields except for nickel and cobalt in the presence of considerable amounts of silicon. Soluble wastes consist of potassium/sodium sulfates/chlorides. Solid wastes correspond to about 4 wt% of the catalyst and can be discarded in industrial dumps.

Nanoparticle-coated organic-inorganic microparticles: experimental design and gastrointestinal tolerance evaluation

The influences of the spray-drying parameters and the type of nanoparticles (nanocapsules or nanospheres) on the characteristics of nanoparticle-coated diclofenac-loaded microparticles were investigated by using a factorial design 3². Gastrointestinal tolerance following oral administration in rats was evaluated. Formulations were selected considering the best yields, the best encapsulation efficiencies and the lowest water contents, presenting surfaces completely coated by nanostructures and a decrease in the surface areas in relation to the uncoated core. In vitro drug release demonstrated the influence of the nanoparticle-coating on the dissolution profiles of diclofenac. Nanocapsule-coated microparticles presented a protective effect on the gastrointestinal mucosa.

Influência do método de extração nos teores de metilxantinas em erva-mate (Ilex paraguariensis a. St.-Hil., aquifoliaceae)

Ilex paraguariensis A. St. -Hil. is a native species of southern South America. The caffeine content in Ilex paraguariensis leaves has been considered an important quality parameter for maté-derived products. In this work different extraction methods for the determination of these methylxantines are compared. The influence of the extraction conditions on the methylxanthine yields was evaluated. Extraction by decoction with acidic aqueous solution (H2SO4 4N) presented the higher efficiency in the theobromine extraction. The extraction in a Soxhlet with acidic aqueous solution and decoction with acidic aqueous solution showed the highest caffeine yield. For the concomitant theobromine and caffeine quantification, the decoction with acidic aqueous solution is suggested.

Parâmetros operacionais no processamento de zeólitas desativadas por fusão com KHSO4

This work presents a study on the determination of the optimal experimental conditions for processing spent commercial zeolites in order to recover lanthanide elements and eventually other elements. The process is based on the fusion of the sample with potassium hydrogenosulfate (KHSO4). Three experimental parameters were studied: temperature, reaction time and catalyst/flux mass ratio. After fusion the solid was dissolved in water and the amount of insoluble matter was used to determine the efficiency of the process. The optimized experimental parameters depend on the composition of the sample processed. Under such conditions the insoluble residue corresponds to SiO2. Lanthanide elements and aluminum present in solution were isolated by conventional precipitation techniques; the yields were at least 75 wt%. The final generated wastes correspond to neutral colorless solutions containing alkali chlorides/sulfates and solids that can be disposed of in industrial dumps.

Influência da temperatura de secagem sobre o rendimento e a composição química do óleo essencial de Tanaecium nocturnum (barb. Rodr.) bur. & K. Shum

The yields and chemical compositions of the essential oils obtained by steam distillation of the fresh and dried (30 and 40 ºC) leaves, stems and roots of Tanaecium nocturnum are reported. The identification and quantification of the volatile constituents were accomplished by GC/MS and GC/FID, respectively. The essential oils obtained from the various parts of the plant were constituted mainly of benzaldehyde. Large losses and variations in the quantities of the components during the drying process were observed. The presence of mandelonitrile in higher concentration in the stem and roots indicates that this species produces cyanogenic glycosides.

Efeito de microondas na estrutura cristalina e na atividade catalítica de argilas

The effect of microwave (MW) irradiation on the crystalline structure of two natural clays and one commercial clay, Montmorillonite K10, was analyzed comparing the X-ray diffraction, N2 isotherms, NMR-MAS of 27Al and 29Si spectra of the clays before and after MW irradiation. The preparation of dioxolane ketals of isatin was used to analyze the MW effect on the catalyst activation. The yields achieved using catalysts activated by MW irradiation were lower (2 to 5%) than the yields achieved using catalysts activated by heat in a conventional oven.

Ciclização do lapachol induzida por sais de tálio III

This work describes the cyclization of lapachol (1) induced by thallium triacetate (TTA) and thallium trinitrate (TTN) in several solvents using magnetic stirring and under microwave irradiation. alpha-Xyloidone (2) - dehydro-alpha-lapachone - was obtained as the main product in these reactions in 20 75% yield. However, rhinacanthin-A (4) was isolated as main product in a 40% yield, using TTA and acetic anhydride:water (1:1) as solvent, and dehydro-iso-alpha-lapachone (3) in 21% yield, using TTA and dichloromethane as solvent. The reaction time decreased drastically under microwave conditions, but the yields of these reactions were not the expected.