HPLC Studies on the Organic Subset of the Oscillatory BZ Reaction. 2. Two Different Types of Malonyl Radicals in the Ce⁴⁺−Malonic Acid Reaction

Abstract

Applying combined HPLC and NMR techniques, it was found that, besides the already known 1,1,2,2-ethanetetracarboxylic acid (ETA), monomalonyl malonate (MAMA) is also a product of the Ce4+−malonic acid reaction. This is indirect evidence that two different types of organic radicals are formed in the reaction: the alkyl and the carboxylato malonyl radicals. While ETA is a recombination product of two alkyl radicals, MAMA is formed in the recombination of one alkyl and one carboxylato radical.

The Importance of Mesomerism in the Termination ofα-Carboxymethyl Radicals from Aqueous Malonic and Acetic Acids

“…Two recombination products, ethane-1,1,2,2-tetracarboxylic acid (2,3-dicarboxysuccinic acid) and monomalonyl malonate (malonic acid dicarboxymethyl monoester), have been observed upon oxidation of malonic acid with Ce IV in aqueous solution. [10] From this it was inferred that two distinct species of malonic acid-derived free radicals, both of them undergoing recombination reactions, exist in these systems, namely, . CH(COOH) 2 and HO 2 CCH 2 ÀC(O)O .…”

“…CH(COOH) 2 and HO 2 CCH 2 ÀC(O)O . in varying states of protonation depending on the pH, either generated independently [10] or tautomerically related.…”

“…1,1,2,2-Ethanetetracarboxylic acid was obtained by hydrolysis of the ester. [10] Monomalonyl malonate was synthesised from malonic acid and hydroxymalonic acid by condensation, with P 2 O 5 as the dehydrating agent. [10] The crude product still contains malonic and hydroxymalonic acid.…”

Kinetic study of the Ce(III)-, Mn(II)- or Fe(phen)32+-catalyzed Belousov-Zhabotinsky reaction with ethyl hydrogen malonate

“…Subsequent O " B CCOOEt reactions (s6 -s10) of radical rationalize O " B CCOOEt the production of propanoic acid (EtCOOH). The generation of carboxylate radical (O " CEtCOOD) via a rearrangement reaction (s6) of radical is O " B COOEt similar to the hypothesis of the carboxylate malonyl radical (CH 2 COOHCOOD) in the Ce(IV) -MA reaction [23].…”

Role of Dibromomalonic Acid in the Photosensitivity of the Ru(bpy)32+-Catalyzed Belousov−Zhabotinsky Reaction

“…Therefore, neither the identity of the products of reaction R23 or the neglect of reaction R27 has a significant effect on our simulations. To test whether the products of reaction R22 are important, we replaced reaction R22 by R22a with the same rate constant k 22 . We found no changes in the results.…”