RESUMEN
Long-flying sparks are an essential part of several pyrotechnic effects. Unfortunately, and in contrast to colored flames, the color space of sparks is basically limited to the black body curve. With low-boiling-point metals, vapor-phase combustion and bright colorful flashes are achievable. Since 1999, alloys of rare-earth elements have been proposed for colorful spark generation. To the best of our knowledge, here, we present the first investigation of such alloys to change the color of sparks beyond the black body limit. Alloys consisting of >65 at. % of a brightly emitting and low-boiling-point metal and a carrier metal allow achieving long-flying deeply colored sparks. Besides the color, branching of sparks is crucial for the visual appearance. Rare-earth metals were found to promote branching of different alloys. Finally, fountains ejecting golden/green sparks based on a stable eutectic Yb-Cu alloy and continuously branching sparks based on Nd2Fe14B are presented.
RESUMEN
Chemical modification of wood applying benzotriazolyl-activated carboxylic acids has proven to be a versatile method for the durable functionalization of its lignocellulosic biopolymers. Through this process, the material properties of wood can be influenced and specifically optimized. To check the scope and limitations of this modification method, various benzamide derivatives with electron-withdrawing (EWG) or electron-donating (EDG) functional groups in different positions of the aromatic ring were synthesized and applied for covalent modification of Scots pine (Pinus sylvestris L.) sapwood in this study. The bonded amounts of substances (up to 2.20 mmol) were compared with the reactivity constants of the Hammett equation, revealing a significant correlation between the modification efficiency and the theoretical reactivity constants of the corresponding aromatic substitution pattern. The successful covalent attachment of the respective substituted benzamides was proven by attenuated total reflection infrared (ATR-IR) spectroscopy, while the stability of the newly formed ester bond was proven in a standardized leaching test.
RESUMEN
Timber is constantly exposed to environmental influences under outdoor conditions which limits its lifetime and usability. In order to counteract the damaging processes caused by insects, we have developed a novel and more environmentally friendly method to protect wood materials via covalent modification by organic insecticides. Starting with an important class of synthetic insecticides which are derived from the natural insecticide nicotine, various new carboxylic acid derivatives of imidacloprid were made accessible. These activated neonicotinoids were utilized for the chemical modification of wood hydroxy groups. In contrast to conventional wood preservation methods in which biocides are only physically bound to the surface for a limited time, the covalent fixation of the preservative guarantees a permanent effect against wood pests, demonstrated in standardized biological tests. Additionally, the environmental interaction caused by non-bound neonicotinoids is significantly reduced, since both, a smaller application rate is required and leaching of the active ingredient is prevented. By minimizing the pest infestation, the lifetime of the material increases while preserving the natural appearance of the material.
RESUMEN
A new chiral thiohydantoin catalyst is used for the stereoselective iodoamination of alkenes. N-iodosuccinimide as the source of the electrophilic iodine is activated by catalytic amounts of different additives which also influence the regioselectivity of some cyclizations.
