Single-walled carbon nanotube formation on iron oxide catalysts in diffusion flames

Single-walled carbon nanotubes (SWCNTs) are shown to grow rapidly on iron oxide catalysts on the fuel side of an inverse ethylene diffusion flame. The pathway of carbon in the flame is controlled by the flame structure, leading to formation of SWCNTs free of polycyclic aromatic hydrocarbons (PAH) or soot. By using a combination of oxygen-enrichment and fuel dilution, fuel oxidation is favored over pyrolysis, PAH growth, and subsequent soot formation. The inverse configuration of the flame prevents burnout of the SWCNTs while providing a long carbon-rich region for nanotube formation. Furthermore, flame structure is used to control oxidation of the catalyst particles. Iron sub-oxide catalysts are highly active toward SWCNT formation while Fe and Fe₂O₃ catalysts are less active. This can be understood by considering the effects of particle oxidation on the dissociative adsorption of gas-phase hydrocarbons. The optimum catalyst particle composition and flame conditions were determined in near real-time using a scanning mobility particle sizer (SMPS) to measure the catalyst and SWCNT size distributions. In addition, SMPS results were combined with flame velocity measurement to measure SWCNT growth rates. SWCNTs were found to grow at rates of over 100 μm/s.     

Nickel-Catalyzed Enantioselective Decarboxylative Acylation: Rapid,Modular Access to α-Amino Ketones**

A new approach to the enantiocontrolled synthesis of α-amino ketone derivatives is disclosed by employing a decarboxylative acylation strategy. Thus, when an acyl chloride and an α-amido-containing redox-active ester are exposed to a nickel catalyst, chiral ligand, and metal reductant, α-amido ketones are produced in good yield and high ee. The reaction exhibits broad substrate scope, can be easily scaled up, and is applied to dramatically simplify the synthesis of several known structures.     

Scalable Electrochemical Decarboxylative Olefination Driven by Alternating Polarity**

A mild, scalable (kg) metal-free electrochemical decarboxylation of alkyl carboxylic acids to olefins is disclosed. Numerous applications are presented wherein this transformation can simplify alkene synthesis and provide alternative synthetic access to valuable olefins from simple carboxylic acid feedstocks. This robust method relies on alternating polarity to maintain the quality of the electrode surface and local pH, providing a deeper understanding of the Hofer-Moest process with unprecedented chemoselectivity.