Aerobic Oxidation Reactivity of Well-Defined CoII and CoIII Aminophenol Complexes

This article describes the synthesis and reactivity studies of three cobalt complexes bearing aminophenol-derived ligands without nitrogen substitution: CoII(tBu2APH)2(tBu2AP)2 (1), Co2III(tBu2APH)2(tBu2AP)2(μ-tBu2BAP)2 (2), and CoIII(tBu2AP)3 (3) (tBu2APH = 2-amino-4,6-di-tert-butylphenol, tBu2AP = 2-amino-4,6-di-tert-butylphenolate, μ-tBu2BAP = bridging 2-amido-4,6-di-tert-butylphenolate). Stoichiometric reactivity studies of these well-defined complexes demonstrate the catalytic com-petency of both CoII and CoIII complexes in the aerobic oxidative cyclization of tBu2APH with tert-butyl isonitrile. Reactions with O2 reveal the aerobic oxidation of CoII complex 1 to generate the CoIII species 2 and 3. UV-visible time-course studies and EPR spectroscopy indicate that this oxidation proceeds through a ligand-based radical intermediate. These studies repre-sent the first example of well-defined cobalt-aminophenol complexes that participate in catalytic aerobic oxidation reactions and highlight a key role for a ligand radical in the oxidation sequence.

Ignition Studies on High-Vitrinite and High-Inertinite Coals Using TGA/DSC, DTIF, EFR, and 20 L Dust Explosive Chamber

The aim of this work was to study the ignition behaviour of eight coals of different coal ranks, petrographic compositions, and places of origin. The research allows us to gain deeper insight into the ignition mechanism and the relationship between certain properties of coals and their behaviour during ignition. The methodology utilised standard fuel ASTM data, petrographic analysis, pyrolysis and oxidation reactivity, and ignition characteristics generated through lab-scale tests using various ignition measurement methods. The results show that, in the dust explosion, a homogeneous ignition of coal dust took place. The ignition potential was the highest for coals with a high content of liptinites and a low content of inertinites. The ranking of coals in terms of ignition potential under these conditions can be determined on the basis of the measurements of the devolatilization rate. During the combustion of coal dust in TGA/DSC, a dust cloud, and a pulverised fuel stream, the ignition of particles was performed according to a heterogeneous mechanism. The study showed that the reflectance index may be the most reliable method of predicting and comparing ignition temperatures of both vitrinite-rich and inertinite-rich coals. Due to the lack of regularity in the ignition temperatures of some coals, depending on the proportion of inertinites, the petrographic composition of coal cannot be used to predict ignition temperatures during the combustion of coal dust. The ranking of the coals according to their ignition potential can be determined using TGA/DSC.