Avaliação de métodos titulométricos para determinação do grau de desacetilação em quitosana Evaluation of titulometric methods for determination of deacetylation´s degree in chitosan
3‐(4‐carboxyphenyl)‐1‐methyltriazene N‐oxide reacts with KOH in methanol/pyridine to give {K[O2C‐C6H4‐N(H)NN(CH3)O]·4H2O}n, Potassium‐3‐(4‐carboxylatophenyl)‐1‐methyltriazene N‐oxide). The terminal carboxylato group of the anion does not interact with the cation. In the crystal lattice of {K(C8H8N3O3)·4H2O}n each three of the four water molecules interact with two potassium cations, every K+ ion being the centre of six bridging K···O interactions. Potassium cations interact further with the terminal N‐oxigen atom of single [C8H8N3O3]− anions achieving two parallel {C8H8N3O3−K+}n chains, which are linked through water molecules. The resulting polymeric, one‐dimensional chain, is operated by a screw axis 21 parallel to the crystallographic direction [010], along and equidistant to the K+ centres. The coordination of the K+ centres involves a distortion of the boat conformation of elementary sulfur (S8) with the ideal C2v symmetry.
products stored in small flasks which cannot accommodate labels large enough to bear all information required by the Globally Harmonised System of Classification, Labelling and Packaging of Chemicals (GHS) are used in academic laboratories. To overcome this restriction Brazilian legislation permits communication of the dangers of chemical products to trained laboratory workers/students by alternative means. Here we describe an alternative label system, developed by the German Social Accident Insurance (DGUV), which allows hazard communication to trained workers/students via a labelling system, using pictograms and highly condensed hazard statements to alert about dangerous chemical products.
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