Aplicação de extratos brutos de flores de quaresmeira e azaléia e da casca de feijão preto em volumetria ácido-base. Um experimento para cursos de análise quantitativa

Crude extract of Tibouchina granulosa, Rhododendron simsii and Phaseolus vulgaris L. were prepared and used as alternative indicators in quantitative analysis teaching in standardization of NaOH solutions and in the determination of acetic acid contents in vinegar. Effect of using such natural extracts as indicators was very attractive to the students and the quantitative results were compared with conventional indicators with good agreement. Concepts of data statistics can successfully be discussed using the interest revived by the use of natural indicators.

Identificação de pigmentos naturais de espécies vegetais utilizando-se cromatografia em papel

The use of natural dyes to demonstrate principles of paper chromatography is proposed. Extraction of the coloring compounds were performed in order to obtain the aglycone form of the anthocyanins present in the crude extracts. Separations were carried out on chromatographic paper with BAW (butanol/acetic acid/water) as mobile phase and the results compared with literature data. The crude extracts were obtained from Tibouchina granulosa, Rododhendron simsii, Impatiens walleriana flowers which are wildely found in Brazil and Phaseolus vulgaris L. grains skin which is the principal ingredient of the world famous "feijoada". Such species were chosen in order to attract the students attention since they are present in their quotidian, in agreement with the new proposals for Brazilian education.

Catalytic gasification of glycerol in supercritical water

The conversion of glycerol in supercritical water (SCW) was studied at 510-550 °C and a pressure of 350 bars using both a bed of inert and non-porous ZrO2 particles (hydrothermal experiments), and a bed of a 1% Ru/ZrO2 catalyst. Experiments were conducted with a glycerol concentration of 5 wt% in a continuous isothermal fixed-bed reactor at a residence time between 2 and 10 s. Hydrothermolysis of glycerol formed water-soluble products such as acetaldehyde, acetic acid, hydroxyacetone and acrolein, and gases like H2, CO and CO2. The catalyst enhanced the formation of acetic acid, inhibited the formation of acrolein, and promoted gasification of the glycerol decomposition products. Hydrogen and carbon oxides were the main gases produced in the catalytic experiments, with minor amounts of methane and ethylene. Complete glycerol conversion was achieved at a residence time of 8.5 s at 510 °C, and at around 5 s at 550 °C with the 1 wt% Ru/ZrO2 catalyst. The catalyst was not active enough to achieve complete gasification since high yields of primary products like acetic acid and acetaldehyde were still present. Carbon balances were between 80 and 60% in the catalytic experiments, decreasing continuously as the residence time was increased. This was attributed partially to the formation of methanol and acetaldehyde, which were not recovered and analyzed efficiently in our set-up, but also to the formation of carbon deposits. Carbon deposition was not observed on the catalyst particles but on the surface of the inert zirconia particles, especially at high residence time. This was related to the higher concentration of acetic acid and other acidic species in the catalytic experiments, which may polymerize to form tar-like carbon precursors. Because of carbon deposition, hydrogen yields were significantly lower than expected; for instance at 550 °C the hydrogen yield potential was only 50% of the stoichiometric value.

Biohajoavat kompleksinmuodostajat mekaanisen massan peroksidivalkaisussa

Mekaanisen massan peroksidivalkaisussa on perinteisesti käytetty kahta kompleksinmuodostajaa, jotka ovat dietyleenitriamiinipentaetikkahappo (DTPA) ja etyleenidiamiinipentaetikkahappo (EDTA). Kompleksinmuodostajat saavat aikaan hyvän kelatointituloksen muodostamalla valkaisulle haitallisten metalli-ionien kanssa kompleksin ja estäen näin metalli-ionien valkaisutulosta huonontavan vaikutuksen. Perinteiset kompleksinmuodostajat DTPA ja EDTA eivät kuitenkaan ole biohajoavia ja niiden epäillään irrottavan metalleja vesistöjen sedimenteistä. Työssä selvitettiin kolmen eri biohajoavan kompleksinmuodostajan valkaisuteho verrattuna perinteisiin kompleksinmuodostajiin. Laboratoriossa suoritetut pesukokeet osoittivat, että mikään biohajoava kompleksinmuodostaja ei saavuttanut samaa pesutehoa kuin perinteiset kompleksinmuodostajat. Valkaisukokeet kuitenkin osoittivat, että biohajoava kompleksinmuodostaja ISA pääsi hyvin lähelle perinteisten kompleksinmuodostajien valkaisutuloksia suoritettaessa valkaisu siten, että massa esipestään kompleksinmuodostajalla ja sen jälkeen valkaistaan vakiokemikaaliannoksella alkalina ollessa natriumhydroksidi. Kaksi muuta biohajoavaa kompleksinmuodostajaa, ISA+EDDS ja HAS, eivät saavuttaneet samaa tasoa. HAS toimi kyllä stabilaattorina, muttei pystynyt nostamaan massan vaaleutta.

Desenvolvimento de um sistema automatizado para a fabricação de filmes automontados

In this technical note, we describe the construction of a low-cost computer controlled device for layer-by-layer film fabrication. The software allows to control multiple material deposition, washing and drying steps and the time for each operation. To test the device, we produced and characterized self-assembled films of conductive polymers by alternating poly(o-methoxyaniline) (POMA) and poly(3-thiophene acetic acid) (PTAA) via the layer-by-layer technique.

Determinación de cinc a microescala en un medicamento especifico

This work presents zinc determination in certain medicines that contain zinc oxide and zinc undecylenate. The technique consists of a spectrophotometric micro-scale titration, where EDTA is used as titrant, and xylenol orange as an indicator, in a medium adjusted to pH = 6 with acetic acid and sodium acetate. After each added portion of EDTA, the absorbance value is measured at a selected wavelength, in order to detect the end-point of the spectrophotometric titration. The results already obtained are satisfactory and promote student's interest. An additional contribution intends to propose the use of micro-scale techniques.

Atualizando a química orgânica experimental da licenciatura

The present contribution describes three different modern experiments for possible adoption in undergraduate organic chemistry laboratories. These are: 1. electrocatalytic hydrogenation of benzaldehyde to benzyl alcohol; 2. identification of three volatile components, obtained from pineapple fruit, by mass spectrometry and 3. microwave mediated fast synthesis of N-(p-chlorophenyl)phthalamic acid from phthalic anhydride and p-chloroaniline under solvent-free conditions. The experiments can be executed in a short period of time, putting the undergraduate student in contact with a variety of topics in organic chemistry and several techniques of analysis, showing multidisciplinarity in organic chemistry.

Determinação direta de molibdênio em comprimidos polivitamínicos por voltametria em meio não aquoso

Adsorptive stripping voltammetry carried out in a homogeneous ternary solvent composed of N,N-dimethylformamide, water and ethanol, with alpha-benzoinoxime (alphaBO) as the complexing agent for Mo(VI) and a 0.5 mol L-1 acetic acid - sodium acetate buffer as supporting electrolyte was successfully used for the determination of molybdenum in polyvitamin-polymineral tablets. Tablet samples were analyzed and the results were compared with those obtained both by graphite furnace atomic absorption and by recovery tests, with good correlations, indicating that this may be considered as an alternative procedure for routine determination of Mo(VI) in pharmaceutical samples.

Determinação da origem biossintética de ácido acético através da técnica "Site Specific Natural Isotopic Fractionation Studied by Nuclear Magnetic Resonance (SNIF-NMR)"

The main purpose of this work is to describe the use of the technique Site-Specific Natural Isotopic Fractionation of hydrogen (SNIF-NMR), using ²H and ¹H NMR spectroscopy, to investigate the biosynthetic origin of acetic acid in commercial samples of Brazilian vinegar. This method is based on the deuterium to hydrogen ratio at a specific position (methyl group) of acetic acid obtained by fermentation, through different biosynthetic mechanisms, which result in different isotopic ratios. We measured the isotopic ratio of vinegars obtained through C3, C4, and CAM biosynthetic mechanisms, blends of C3 and C4 (agrins) and synthetic acetic acid.

O emprego de quitosana quimicamente modificada com anidrido succínico na adsorção de azul de metileno

The adsorption capacity of alpha-chitosan and its modified form with succinic anhydride was compared with the traditional adsorbent active carbon by using the dye methylene blue, employed in the textile industry. The isotherms for both biopolymers were classified as SSA systems in the Giles model, more specifically in L class and subgroup 3. The dye concentration in the supernatant in the adsorption assay was determined through electronic spectroscopy. By calorimetric titration thermodynamic data of the interaction between methyene blue and the chemically modified chitosan at the solid/liquid interface were obtained. The enthalpy of the dye/chitosan interaction gave 2.47 ± 0.02 kJ mol-1 with an equilibrium constant of 7350 ± 10 and for the carbon/dye interaction this constant gave 5951 ± 8. The spontaneity of these adsorptions are reflected by the free Gibbs energies of -22.1 ± 0.4 and -21.5 ± 0.2 kJ mol-1, respectively, found for these systems. This new adsorbent derived from a natural polysaccharide is as efficient as activated carbon. However 97% of the bonded dye can be eluted by sodium chloride solution, while this same operation elutes only 42% from carbon. Chitosan is efficient in dye removal with the additional advantage of being cheap, non-toxic, biocompatible and biodegradable.

Metodologia para análise simultânea de ácido nicotínico, trigonelina, ácido clorogênico e cafeína em café torrado por cromatografia líquida de alta eficiência

A reverse phase liquid chromatography method was developed for simultaneous determination of trigonelline, caffeine, nicotinic and chlorogenic (5-CQA) acids in roasted coffee. A gradient of acetic acid/acetonitrile was used as mobile phase and detection was carried out in the UV. The samples were extracted with acetonitrile/water (5:95 v/v) at 80 ºC/10 min. Good recovery (89 to 104%), repeatability and linearity were obtained. Detection limits of 0.01, 0.15, 0.04 and 0.04 mg mL-1 were observed for nicotinic acid, trigonelline, 5-CQA and caffeine. The method, applied to arabica and robusta coffees with different degrees of roasting, was efficient and fast (~35 min) and also allowed identification of cinnamic acids.

Water circulations for effective bleaching of high-brightness mechanical pulps

The amount of water available is usually restricted, which leads to a situation where a complete understanding of the process, including water circulations and the influence of water components, is essential. The main aim of this thesis was to clarify the possibilities for the efficient use of residual peroxide by means of water circulation rearrangements. Rearranging water circulations and the reduction of water usage may cause new problems, such as metal induced peroxide decomposition that needs to be addressed. This thesis introduces theoretical methods of water circulations to combine two variables; effective utilization of residual peroxide and avoiding manganese in the alkaline peroxide bleaching stage. Results are mainly based on laboratory and mill site experiments concerning the utilization of residual peroxide. A simulation model (BALAS) was used to evaluate the manganese contents and residual peroxide doses. It was shown that with optimum recirculation of residual peroxide the brightness can be improved or chemical costs can be decreased. From the scientific perspective, it was also very important to discover that recycled peroxide was more effective pre-bleaching agent compared to fresh peroxide. This can be due to the organic acids i.e. per acetic acid in wash press filtrate that have been formed in alkaline bleaching stage. Even short retention time was adequate and the activation of residual peroxide using sodium hydroxide was not necessary. There are several possibilities for using residual peroxide in practice regarding bleaching. A typical modern mechanical pulping process line consist of defibering, screening, a disc filter, a bleach press, high consistency (HC) peroxide bleaching and a wash press. Furthermore there usually is not a particular medium consistency (MC) pre-bleaching stage that includes additional thickening equipment. The most advisable way to utilize residual peroxide in this kind of process is to recycle the wash press filtrate to the dilution of disc filter pulp (low MC pre-bleaching stage). An arrangement such as this would be beneficial in terms of the reduced convection of manganese to the alkaline bleaching stage. Manganese originates from wood material and will be removed to the water phase already in the early stages of the process. Recycling residual peroxide prior to the disc filter is not recommended because of low consistencies. Regarding water circulations, the novel point of view is that, it would be beneficial to divide water circulations into two sections and the critical location for the division is the disc filter. Both of these two sections have their own priority. Section one before the disc filter: manganese removal. Section two after the disc filter: brightening of pulp. This division can be carried out if the disc filter pulp is diluted only by wash press filtrate before the MC storage tower. The situation is even better if there is an additional press after the disc filter, which will improve the consistency of the pulp. This has a significant effect on the peroxide concentration in the MC pre-bleaching stage. In terms of manganese content, it is essential to avoid the use of disc filter filtrate in the bleach press and wash press showers. An additional cut-off press would also be beneficial for manganese removal. As a combination of higher initial brightness and lower manganese content, the typical brightness increase varies between approximately 0.5 and 1% ISO units after the alkaline peroxide bleaching stage. This improvement does not seem to be remarkable, but as it is generally known, the final brightness unit is the most expensive and difficult to achieve. The estimation of cost savings is not unambiguous. For example in GW/TMP mill case 0.6% ISO units higher final brightness gave 10% savings in the costs of bleaching chemicals. With an hypothetical 200 000 ton annual production, this means that the mill could save in the costs of bleaching chemicals more than 400 000 euros per year. In general, it can be said that there were no differences between the behavior of different types of processes (GW, PGW, TMP and BCTMP). The enhancement of recycling gave a similar response in all cases. However, we have to remember that the utilization of residual peroxide in older mills depends a great deal on the process equipment, the amount of water available and existing pipeline connections. In summary, it can be said that processes are individual and the same solutions cannot be applied to all cases.

Estudo de recuperação de glifosato e AMPA derivados em solo utilizando-se resinas nacionais

In the present paper we studied the recoveries of glyphosate, N-(phosphonomethyl)glycine (GLY) and its major metabolite, (aminomethyl)phosphonic acid (AMPA) in soil using national (Brazilian) ion-exchange resins, derivatization by a mixture of trifluoroacetic anhydride and trifluoroethanol and analyses by GC-MS. The quantification limits were 12 ng.g-1 for both compounds and the methodology showed a range of recuperation from 85 to 94% with coefficients of variation (CV) ranging from 4.07 to 6.91% for GLY. For AMPA, the mean recoveries ranged from 87 to 102% with CVs ranging from 5.81 to 6.99%. Additional studies showed that, due to the instability of the derivatized compounds, they must be analysed keeping constant time between derivatization and analysis, preferably less than 24 h.

Synthesis and characterization of new amino acyl-4-thiazolidones

A series of heterocyclic compounds with a 4-thiazolidone nucleus and amino acyl moiety were synthesized by protection reaction of thiosemicarbazide using the symmetrical anhydride (Boc)2O and cyclization with chloroacetic acid under mild conditions. Trifluoroacetic acid was used to obtain 4-thiazolidone and the alpha-amino acid condensation reactions were carried out using strategies for peptide synthesis. The characterization of this new class of compounds was performed using IR and ¹H-NMR spectroscopy.

Síntese e avaliação da propriedade reguladora de crescimento vegetal de compostos indólicos derivados do safrol

The present work describes the use of piperonal, a derivative of the secondary metabolite safrole, for the synthesis of new 5,6-methylenedioxysubstituted indole carboxylic acids structurally related to the indol-3-yl-acetic acid (AIA, I). The route comprises six steps beginning with piperonal with an overall yield of 19%. Compound IX was tested towards its plant growth regulator properties in bioassays specific for auxine activity. The in vitro assays were performed in a germination chamber and were of two types: root growth in germinated seeds of Lactuca sativa, Cucumbis sativus and Raphanus sativus and peciole biotest using Phaseolus vulgaris.