Ultraschnelle Decarboxylierung organischer Peroxide in Lösung: Zusammenspiel unterschiedlicher spektroskopischer Techniken, Quantenchemie und theoretischer Modellierung

Abstract

Die Initiatoreffektivität in radikalischen Polymerisationen wird von den Zeitskalen der Bildung und der nachfolgenden Reaktionen intermediärer Radikale bestimmt, die beim Zerfall organischer Peroxide auftreten. Die photoinduzierte mehrstufige Decarboxylierung organischer Peroxide (z. B. Dinaphthoylperoxid, siehe Schema) in Lösung wurde in Echtzeit verfolgt und mit quantenchemischen Methoden analysiert.

Initiation of free‐radical polymerization by peroxypivalates studied by electrospray ionization mass spectrometry

“…The two radicals may combine to form an ether or may undergo a disproportionation reaction, with both these processes consuming free radicals and thus being associated with a lowering of initiator efficiency 3. In very recent studies decarboxylation was investigated for intermediate arylcarbonyloxy radicals via pump‐probe experiments on a fs to ps timescale 4–6. These highly time‐resolved experiments were accompanied by DFT calculations of the decarboxylation dynamics to derive a detailed understanding of this unimolecular process on the ps–ns timescale.…”

Decarboxylation of carbonyloxy radicals: a density functional study

“…Large organic peroxides are molecules not only of strong fundamental, but also of considerable industrial interest due to their widespread use as initiators in free-radical polymerizations. [1][2][3][4] The decomposition of peroxides of type RC(O)O-O-tert-butyl with R being an aryl compound [5][6][7][8] into the three species R , tert-butyl and CO 2 can in principle occur via a concerted or a stepwise mechanism. It is now accepted that the latter mechanism is the rule in RC(O)O-O-tert-butyl decay so that intermediate carbonyloxy radicals, RCO 2 , that are formed after O-O bond fission play a key role in this process.…”

“…It is now accepted that the latter mechanism is the rule in RC(O)O-O-tert-butyl decay so that intermediate carbonyloxy radicals, RCO 2 , that are formed after O-O bond fission play a key role in this process. The carbonyloxy radical might subsequently decarboxylate to form CO 2 and the radical R. Investigations on substituted aroyloxy radicals in solution yield lifetimes in the nanosecond to microsecond range, 7,9,10 which allow these intermediates to escape the solvent cage and initiate the polymerization. Shorter (ps) lifetimes have been attributed to 9-methylfluorenylcarbonyloxy, 11 benzylcarbonyloxy and benziloxy radicals.…”

Macromolecular Chemistry: Buback honored / Physical Chemistry: Stubenrauch awarded

“…radical polymerization in supercritical CO 2 ), as well as on reaction kinetics in general. He recently reported in Angewandte Chemie on the interplay of spectroscopy, quantum chemistry, and theory in the ultrafast decarboxylation of organic peroxides in solution 1a. and in Macromolecular Chemistry and Physics on the termination kinetics of the radical polymerization of butyl methacrylates 1b…”