Controlled radical polymerization in the presence of N‐oxyls

Recent development in controlled radical polymerization has provided a tool to combine a relatively robust radical polymerization technique with structural control. This contribution focuses on stable free radical polymerization in the presence of nitroxides. The influence of 2,2,6,6‐tetramethyl‐piperidine‐N‐oxyl (TEMPO) and temperature on the copolymerization of styrene and acrylonitrile will be discussed. In the second part a new class of nitroxide stable free radicals will be presented that shows enhanced performance in styrene polymerizations.     

NO Reactions Inside Crystals

Reactions of chemisorbed reagents inside the crystalline molecular solid state are rare but offer unexploited methods for selective solvent-free chemical synthesis. Here we show that the greenhouse gas precursor, nitric oxide (NO) is chemisorbed by crystals of the hexafluorophosphate salts of complexes containing dicobalt sites. On NO sorption a cascade of reactions results in the in-crystal synthesis of nitrite and other gaseous NO_x. Recrystallization enabled structural elucidation of the mixed valent {[(bpbp)Co₂(μ-(η¹-O : η¹-N)-ONO)]₂(bdc)}⁴⁺ (bpbp=2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato, bdc=1,4-benzenedicarboxylato) cation. Overlapping signals in the solid-state EPR spectra confirm the Co^IICo^III oxidation state and the presence of NO₂ trapped inside the unrecrystallised solid products (br. g=4, triplet g=2 (340 mT), A(N)=73 MHz), despite three cycles of vacuum and N₂ flushing. Consistently, ν_N−O bands appear in the Raman and IR spectra that are due to the coordinated nitrate and the trapped NO₂ that were synthesized in-crystal. The latter is expelled by heating the solid to 160 °C or by recrystallization. Dimetallic cooperativity is proposed for the NO transformations in these rare examples of selective, chemisorptive substrate reactions in the solid-state.     

Raman microscopic identification of gunshot residues

Raman microscopy was used to identify unambiguously the anions of lead and barium in gunshot residues (ca. 5 μm in size) deposited on cellulosic substrates. It was found that most of the particles consist of mixtures of oxides, sulphate and carbonate (along with carbon). In particular, there is strong evidence for the formation of mixed oxides of iron but only relatively little evidence for oxides of antimony. The Raman technique has been shown to be able to identify individual or mixed components and to confirm the presence of microcrystalline particles with a particular crystal structure (e.g. orthorhombic lead oxide). © 1998 John Wiley & Sons, Ltd.     

ChemInform Abstract: Hydrodesulfurization of FeS+: Predominance of Kinetic over Thermodynamic Control.

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