Dyeing of cellulose with reactive dyes (RDs) is an important commercial process because the fibers/fabrics have vivid colors with excellent fastness, since the RD is covalently bonded to cellulose. The subject of the present study is dying of cotton-polyethylene terephthalate (PET) blends using a flow system where the RD absorbance is contentiously monitored by UV-Vis spectroscopy. This allows the collection of extensive data points (≥ 300) to calculate the rate constants, hence the corresponding activation parameters. At a fixed pH = 11.2, a pseudo second-order rate law fits the absorbance vs. time data satisfactorily. At a constant temperature, the order of the dyeing rate constant (k2) is higher for the blend containing 88.9% cotton. The dyeing activation energy, on the other hand, is higher for the blend containing 50% cotton. These results were attributed to the adverse effects of (hydrophobic) PET on the diffusion of RD into the blend. We calculated an equation that shows the dependence of k2 on the temperature and cotton wt.% of the blend. RDs (RDs fibersfabrics fibers fabrics fastness cottonpolyethylene polyethylene (PET UVVis UV Vis spectroscopy ≥ ( 300 constants parameters 112 11 2 11.2 secondorder second vs satisfactorily k (k2 889 88 9 88.9 energy hand 50 hydrophobic (hydrophobic wt wt. 30 1 11. (k 8 88. 5 3

We developed a project during an undergraduate course (advanced experimental chemistry) on the microwave-assisted synthesis of biodiesel (BD), via base-catalyzed transesterification of coconut fat (CF) and soybean oil (SO) by ethanol, followed by product analysis by gas chromatography/mass spectrometry. Our goals were to introduce a problem with relevant socio-economic impact (production of BD); to discuss and compare methods for biofuel analysis, and to gain insight into transesterification mechanism as an important example of acyl-transfer reactions. Comparison of both BFs showed clear difference in fatty acid composition; that from CF contains shorter, saturated chains (mainly ethyl dodecanoate- and tetradecanoate), whereas biodiesel from SO is essentially composed of longer unsaturated chains (e.g., ethyl oleate and linoleate). The project takes eight hours to complete, is conceptually simple, being suitable for inclusion in the undergraduate science curriculum.

Dipolaridade/polarizabilidade do solvente (SDP) tem sido calculada a partir dos espectros de UV-Vis de 2-(N,N-dimetilamino)-7-nitro-9H-fluoreno e 2-fluoro-7-nitro-9H-fluoreno. Com base em cálculos teóricos (23 solventes) e dados experimentais (56 solventes), revela-se que 2-cloro-7-nitro-9H-fluoreno (disponível comercialmente) pode ser perfeitamente utilizado para o cálculo dessa propriedade, em vez de 2-fluoro-7-nitro-9H-fluoreno. A divisão de SDP nos seus componentes (dipolaridade (SD) e polarizabilidade (SP) do solvente) requer o uso de um composto sintético poliênico cuja síntese é trabalhosa, envolvendo 15 etapas. Nosso grupo de pesquisa mostrou recentemente que o corante natural β-caroteno pode ser convenientemente utilizado para a determinação de SP, permitindo o cálculo de SD. Utilizando estas sondas solvatocrômicas, SDP, SP e SD foram calculados para uma série de 1-bromoalcanos. Para várias séries homólogas, a dependência de SDP (SD e SP para uma série homóloga) com o número de átomos de carbono nos grupos 1-alquila ou acila foi calculada e discutida.

Solvent dipolarity/polarizability (SDP) has been previously calculated from the UV-Vis spectra of 2-(N,N-dimethylamino)-7-nitro-9H-fluorene and 2-fluoro-7-nitro-9H- fluorene. Based on theoretical calculations (23 solvents) and experimental data (56 solvents), it is shown that 2-chloro-7-nitro-9H-fluorene (commercially available) can be conveniently employed for the calculation of this property, instead of its 2-fluoro-7-nitro counterpart. The splitting of SDP into its components (solvent dipolarity (SD) and polarizability (SP)) requires the use of a synthetic polyene compound whose synthesis is laborious, involving 15 steps. Our research group has recently shown that the natural dye β-carotene can be conveniently employed for the determination of SP, allowing the calculation of SD. Using these solvatochromic probes, SDP, SP and SD for a series of 1-bromoalkanes were calculated. For several homologous series, the dependence of solvent SDP (SD and SP for one series) on the number of carbon atoms in the 1-alkyl- or acyl-group was calculated and discussed.

The effects of solvents on chemical phenomena is complex because there are various solute-solvent interaction mechanisms. Solvatochromism refers to the effects of solvents on the spectra of probes. The study of this phenomenon sheds light on the relative importance of the solvation mechanisms. Solvation in pure solvents is quantitatively analyzed in terms of a multi-parameter equation. In binary solvent mixtures, solvation is analyzed by considering the organic solvent, S, water, W, and a 1:1 hydrogen bonded species (S-W). The applications of solvatochromism to understand distinct chemical phenomena, reactivity and swelling of cellulose, is briefly discussed.

Este trabalho apresenta alguns aspectos da acetilação em LiCl/N,N-dimethylacetamida, DMAc de celulose de sisal nativa e mercerizada (sisal e M-sisal). A mercerização da fibra em solução de NaOH resulta nas seguintes alterações: decréscimo de 29.9 % no índice de cristalinidade; diminuição de 16.2% no grau de polimerização e aumento de 9.3% no conteúdo de α-celulose. Estudo com espalhamento de luz de soluções de sisal, M-sisal, celulose microcristalina e algodão mostrou que elas se apresentam na forma de agregados, com números médios de agregação de 5.2, 3.2, 9.8 e 35.3, respectivamente. A presença destes agregados afeta a acessibilidade à celulose durante sua funcionalização. Acompanhamento do grau de substituição, DS, de acetato de celulose em função do tempo, mostrou que o mesmo aumenta por um intervalo de tempo de 5 h, seguido por um decréscimo após 7 h. Possíveis razões para este decréscimo são discutidas. Como esperado, M-sisal apresenta um DS maior que a sisal nativa.

We report here on some aspects of the acetylation in LiCl/N,N-dimethylacetamide, DMAc, of untreated and mercerized sisal cellulose, hereafter designated as sisal and M-sisal, respectively. Fiber mercerization by NaOH solution has resulted in the following changes: 29.9% decrease in the index of crystallinity; 16.2% decrease in the degree of polymerization and 9.3% increase in α-cellulose content. A light scattering study of solutions of sisal, M-sisal, microcrystalline and cotton celluloses in LiCl/DMAc has shown that they are present as aggregates, with (an apparent) average aggregation numbers of 5.2, 3.2, 9.8, and 35.3, respectively. The presence of these aggregates affects the accessibility of cellulose during its functionalization. A study of the evolution of the degree of substitution, DS, of cellulose acetate as a function of reaction time showed an increase up to 5 h, followed by a decrease at 7 h. Possible reasons for this decrease are discussed. As expected, M-sisal gave a higher DS that its untreated counterpart.

The environmental impact of detergents and other consumer products is behind the continued interest in the chemistry of the surfactants used. Of these, linear alkylbenzene sulfonates (LASs) are most widely employed in detergent formulations. The precursors to LASs are linear alkylbenzenes (LABs). There is also interest in the chemistry of these hydrocarbons, because they are usually present in commercial LASs (due to incomplete sulfonation), or form as one of their degradation products. Additionally, they may be employed as molecular tracers of domestic waste in the aquatic environment. The following aspects are covered in the present review: The chemistry of surfactants, in particular LAS; environmental impact of the production of LAS; environmental and toxicological effects of LAS; mechanisms of removal of LAS in the environment, and methods for monitoring LAS and LAB, the latter in domestic wastes. Classical and novel analytical methods employed for the determination of LAS and LAB are discussed in detail, and a brief comment on detergents in Brazil is given.