Exceptionally high decarboxylation rate of a primary aliphatic acyloxy radical determined by radical product yield analysis and quantitative ¹H‐CIDNP spectroscopy

Abstract

Symmetrical (RCO2CO2R; R = XCH2CH2) and asymmetrical (RCO2CO2R′; R = C9H19CH2CH2, R′ = CH3 or m‐ClC6H4) primary diacyl peroxides were thermally decomposed under different conditions to analyze the decarboxylation rates of the thermally generated acyloxy radicals. Quantitative models of the geminate product yields, and qualitative and quantitative 1H‐CIDNP spectroscopy were used to obtain the decarboxylation rate estimates. Results reported here suggest that, unlike short chain acyloxy radicals such as propanoyloxyl, long chain acyloxy radicals possess the highest decarboxylation rates of all known acyloxy radicals, estimated at (0.5–1.5) × 1012 s−1 between 80 and 140 °C. Given the nature of the dissociative state of acyloxy radicals, such rates appear to be the result of destabilization of the former by the steric bulk of the long chain substituents. Additionally, the rate of this order of magnitude suggests a nearly concerted decarboxylation of primary diacyl peroxides. Copyright © 2011 John Wiley & Sons, Ltd.

Direct Detection of a Persistent Carbonyloxyl Radical in the Gas Phase

“…11 For charged dicarboxylate species, including aliphatic,23 substituted aliphatic,20 and aromatic dicarboxylates (Supporting Information), lifetimes for the analogous carbonyloxyl radicals are too short for the detached monoanion radical to be detected using our ion trap, with only decarboxylation and fragmentation products observed. Even in solution, the lifetimes reported for carbonyloxyl radicals range between μs and ps,8, 24, 25, 31 again much shorter than observed here for the acetylene dicarboxylate radical anion.…”

Hydrodecarboxylation of Carboxylic and Malonic Acid Derivatives via Organic Photoredox Catalysis: Substrate Scope and Mechanistic Insight

“…15,16 These radicals are known to rapidly rearrange to expel CO 2 and form carbon-centered radicals. 17,18 On the surface of an electrode, these radicals can be successively oxidized to the corresponding cation, known as the non-Kolbe pathway. 19 …”

Gas-phase studies of metal catalyzed decarboxylative cross-coupling reactions of esters

“…Tunge has recently reported the decarboxylative allylation of amino alkanoic esters using a dual catalyst systems consisting of a palladium catalysis and an iridium photocatalyst (Scheme 10) [89]. A key feature is that photochemical oxidation of the carboxylate anion gives a carboxylate radical, which is known to readily decarboxylate [90,91] to generate a radical intermediate, which then undergoes allylation. This represents a promising new approach to extend the scope of ester substrates that can be used in metal catalyzed decarboxylative alkylation reactions.…”