C3- or C4-hydroxyalkylated phenols are highly reactive towards peroxidation with oxone, which results in the formation of tertiary C3 hydroperoxides. This reaction can also be performed with photochemically generated singlet oxygen. However, other characteristic singlet oxygen reactions do not proceed with caroate. The initially formed hydroperoxides cyclize in the presence of a Lewis acid catalyst based on boron, indium, or iron to give spiroannulated peroxides. These exhibit restricted ring inversion whereas larger nine-membered-ring peroxides are thermally less stable and show higher ring flexibility (according to NMR analysis).
The net oxidising atmosphere of lean burn engines requires a special after-treatment catalyst for NOx removal from the exhaust gas. Lean NOx traps (LNT) are such kind of catalysts. To increase the efficiency of LNTs at low temperatures platinised perovskite-based infiltration composites La0.5Sr0.5Fe1-xMxO3-δ/Al2O3 with M = Nb, Ti, Zr have been developed. In general, platinum based LNT catalysts show an undesired, hazardous formation of N2O in the lean operation mode due to a competing C3H6-selective catalytic reduction (SCR) at the platinum sites. To reduce N2O emissions an additional Rh-coating, obtained by incipient wetness impregnation, besides the Pt coating and a two-layered oxidation catalyst (2 wt.% Pd/20 wt.% CeO2/alumina)-LNT constitution, has been investigated. Though the combined Rh-Pt coating shows a slightly increased NOx storage capacity (NSC) at temperatures above 300 °C, it does not decrease N2O formation. The layered oxidation catalyst-LNT system shows a decrease in N2O formation of up to 60% at 200 °C, increasing the maximum NSC up to 176 µmol/g. Furthermore, the NSC temperature range is broadened compared to that of the pure LNT catalyst, now covering a range of 250–300 °C.
The dichotomy of the dangerous and healthy properties of medium‐sized cyclic peroxides, which are used as medicinal agents and energetic materials, is explained by A. G. Griesbeck et al. in their Communication on page 13770 ff. They attribute the decrease in the gain of stabilization of spirofused and ring‐annulated peroxides (determined from the Gibbs energy difference between starting materials and products) with increasing ring size to the opposing effects of stabilizing natural bond orbital (NBO) interactions and destabilizing ring strain.
C-3-oder C-4-hydroxyalkylierte Phenole sind hochreaktive Substrate fürd ie Hydroperoxierung durch Oxone und führen zur Bildung von tertiären C-4-Hydroperoxiden. Diese Reaktion kann auchm it photochemisch erzeugtem Singulett-Sauerstoff durchgeführt werden. Andere charakteristischeS ingulett-Sauerstoffreaktionen verlaufen jedochn ichtm it Caroat. Die zunächst gebildeten Hydroperoxide werden unter Lewis-Säure-Katalyse mit Bor-, Indiumoder Eisen-basierten Katalysatoren zu spiroverknüpften Peroxiden 6, 9 cyclisiert, die eine eingeschränkte Ringinversion aufweisen, während die grçßeren neungliedrigen Peroxide 12 thermisch weniger stabil sind und -mçglicherweise korreliertauche ine hçhere Ringflexibilitäta ufweisen (durchN MR-Analyse).
Die Dichotomie zwischen medizinischen und explosiven Eigenschaften mittelgroßer cyclischer Peroxide wird von A. G. Griesbeck et al. in ihrer Zuschrift auf S. 13966 ff. erklärt. Der Gewinn an Stabilisierung der spiroverknüpften und ringanellierten cyclischen Peroxide (bestimmt aus der Gibbs‐Energiedifferenz zwischen Ausgangsverbindung und Produkt) nimmt mit zunehmender Ringgröße ab. Der Grund hierfür sind die gegenläufigen Effekte stabilisierender Natural‐Bond‐Orbital(NBO)‐Wechselwirkungen und destabilisierender Ringspannung.
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