Disproportionation

About: Disproportionation is a research topic. Over the lifetime, 6423 publications have been published within this topic receiving 125210 citations. The topic is also known as: dismutation & redox disproportionation.

The chemistry of free radical polymerization

Abstract: Part 1 Free radical reactions: introduction addition to carbon-carbon double bonds steric factors polar factors bond strengths theoretical treatments hydrogen atom transfer polar factors stereoelectronic factors reaction conditions abstraction vs addition summary radical-radical reactions pathways for combination pathways for disproportionation combination vs disproportionation summary Part 2 Initiation: introduction the initiation process reaction with monomer fragmentation reaction with solvents, additives or impurities effects of the reaction medium on radical reactivity reaction with oxygen initiator efficiency cage reaction and initiator-derived by-products primary radical termination transfer to initiator initiation in heterogeneous polymerization thermal initiation the radicals carbon-centred radicals oxygen-centred radicals Part 3 Propagation: introduction stereosequence isomerism - tacticity monoene polymers conjugated diene polymers structural isomerism - rearrangement cyclopolymerization ring-opening polymerization intramolecular atom transfer propagation kinetics and thermodynamics Part 4 Termination introduction radical-radical termination termination kinetics disproportionation vs combination - general considerations disproportionation vs combination - summary chain transfer mechanisms transfer agents transfer to monomer transfer to polymer inhibition and retardation "stable" radicals oxygen Part 5 Copolymerization: introduction statistical copolymerization copolymerization mechanisms block and graft copolymerization end-functional polymers block and graft copolymer synthesis Part 6 Controlling polymerization: introduction "defect structures" in polystyrene "defect structures" in poly(methyl methacrylate) controlling propagation solvent Lewis acids and inorganics template polymers compositional heterogeneity in copolymers agents for controlling termination organosulfur iniferters hexasubstituted ethanes and azo compounds alkoxyamines and related species

Aqueous Room Temperature Metal-Catalyzed Living Radical Polymerization of Vinyl Chloride

Abstract: This paper describes the room-temperature living radical polymerization (LRP) of vinyl chloride in H2O/THF in the presence of Cu0 or CuI salts as catalysts, tren or PEI as ligands, and iodoform as initiator. The disproportionation reaction 2CuI + L → Cu0 + CuII(L) is the crucial step, as it continuously provides the active species for both the initiation (Cu0) and the reversible termination step (CuII). Mn was found to increase linearly with conversion and is in good agreement with Mth, with the Mw/Mn being approximately 1.5.

Bacterial disproportionation of elemental sulfur coupled to chemical reduction of iron or manganese.

Abstract: A new chemolithotrophic bacterial metabolism was discovered in anaerobic marine enrichment cultures. Cultures in defined medium with elemental sulfur (S0) and amorphous ferric hydroxide (FeOOH) as sole substrates showed intense formation of sulfate. Furthermore, precipitation of ferrous sulfide and pyrite was observed. The transformations were accompanied by growth of slightly curved, rod-shaped bacteria. The quantification of the products revealed that S0 was microbially disproportionated to sulfate and sulfide, as follows: 4S0 + 4H2O → SO42- + 3H2S + 2H+. Subsequent chemical reactions between the formed sulfide and the added FeOOH led to the observed precipitation of iron sulfides. Sulfate and iron sulfides were also produced when FeOOH was replaced by FeCO3. Further enrichment with manganese oxide, MnO2, instead of FeOOH yielded stable cultures which formed sulfate during concomitant reduction of MnO2 to Mn2+. Growth of small rod-shaped bacteria was observed. When incubated without MnO2, the culture did not grow but produced small amounts of SO42- and H2S at a ratio of 1:3, indicating again a disproportionation of S0. The observed microbial disproportionation of S0 only proceeds significantly in the presence of sulfide-scavenging agents such as iron and manganese compounds. The population density of bacteria capable of S0 disproportionation in the presence of FeOOH or MnO2 was high, > 104 cm-3 in coastal sediments. The metabolism offers an explanation for recent observations of anaerobic sulfide oxidation to sulfate in anoxic sediments.