Disproportionation

Abstract: Polytriazolylamines were synthesized by the copper(I)-catalyzed ligation of azides and alkynes. The C3-symmetric derivative, TBTA, was shown to be a powerful stabilizing ligand for copper(I), protecting it from oxidation and disproportionation, while enhancing its catalytic activity.

Abstract: Isolated single-wall carbon nanotubes (SWNT) were grown by disproportionation of carbon monoxide at 1200°C, catalyzed by molybdenum particles a few nanometers in size. The tube diameters, ranging from 1 to 5 nm, closely correlated with the size of the catalytic particle found attached to the tube end. This result represents the first experimental evidence of SWNT produced by pre-formed catalytic particles. A mechanism for nucleation that is quite distinct from our recently proposed mechanism of SWNT produced by laser vaporization is advanced for formation of SWNT in the present case.

Abstract: Conventional metal-catalyzed organic radical reactions and living radical polymerizations (LRP) performed in nonpolar solvents, including atom-transfer radical polymerization (ATRP), proceed by an inner-sphere electron-transfer mechanism. One catalytic system frequently used in these polymerizations is based on Cu(I)X species and N-containing ligands. Here, it is reported that polar solvents such as H(2)O, alcohols, dipolar aprotic solvents, ethylene and propylene carbonate, and ionic liquids instantaneously disproportionate Cu(I)X into Cu(0) and Cu(II)X(2) species in the presence of a diversity of N-containing ligands. This disproportionation facilitates an ultrafast LRP in which the free radicals are generated by the nascent and extremely reactive Cu(0) atomic species, while their deactivation is mediated by the nascent Cu(II)X(2) species. Both steps proceed by a low activation energy outer-sphere single-electron-transfer (SET) mechanism. The resulting SET-LRP process is activated by a catalytic amount of the electron-donor Cu(0), Cu(2)Se, Cu(2)Te, Cu(2)S, or Cu(2)O species, not by Cu(I)X. This process provides, at room temperature and below, an ultrafast synthesis of ultrahigh molecular weight polymers from functional monomers containing electron-withdrawing groups such as acrylates, methacrylates, and vinyl chloride, initiated with alkyl halides, sulfonyl halides, and N-halides.

Abstract: The lithium/sulfur battery is a promising electrochemical system that has a high theoretical capacity of 1675 mAh g–1, but its discharge mechanism is well-known to be a complex multistep process. As the active material dissolves during cycling, this discharge mechanism was investigated through the electrolyte characterization. Using high-performance liquid chromatography, UV–visible absorption, and electron spin resonance spectroscopies, we investigated the electrolyte composition at different discharge potentials in a TEGDME-based electrolyte. In this study, we propose a possible mechanism for sulfur reduction consisting of three steps. Long polysulfide chains are produced during the first reduction step (2.4–2.2 V vs Li+/Li), such as S82– and S62–, as evidenced by UV and HPLC data. The S3•– radical can also be found in solution because of a disproportionation reaction. S42– is produced during the second reduction step (2.15–2.1 V vs Li+/Li), thus pointing out the gradual decrease of the polysulfide chai...

Abstract: Bacteria that disproportionate elemental sulfur fractionate sulfur isotopes such that sulfate is enriched in sulfur-34 by 12.6 to 15.3 per mil and sulfide is depleted in sulfur-34 by 7.3 to 8.6 per mil. Through a repeated cycle of sulfide oxidation to S0 and subsequent disproportionation, these bacteria can deplete sedimentary sulfides in sulfur-34. A prediction, borne out by observation, is that more extensive sulfide oxidation will lead to sulfides that are more depleted in sulfur-34. Thus, the oxidative part of the sulfur cycle creates circumstances by which sulfides become more depleted in sulfur-34 than would be possible with sulfate-reducing bacteria alone.