Thermal decomposition of hexamethylenetetramine: mechanistic study and identification of reaction intermediates via a computational and NMR approach

Construction of Nanoflower Cobalt-Based Catalyst for Methane-Free CO Hydrogenation to Hydrocarbon Reaction

Methane and its oxidation product (i. e., CO2) are both greenhouse gases. In the product chain of CO hydrogenation to hydrocarbon reaction, methane is also an unwanted product due to its poor added value. Herein we investigated the effect of structure-directing agent urotropine on cobalt-based catalyst supported on Al-O-Zn type carrier and achieved an initial and pioneering exploration of methane-free CO hydrogenation to hydrocarbon reaction at mild CO conversion range. The catalyst modified by urotropine has a nanoflower micromorphology and can significantly change the reaction performance, almost completely eliminating the ability of the catalyst to inhibit C-C coupling within a mild CO conversion range, that is, it can produce no or less C1-C4 gaseous hydrocarbons, while rich in condensed hydrocarbons (i. e., C5+ hydrocarbon selectivity can reach as high as 92.8 %-100.0 %).

Ruthenium-Induced Decomposition of Hexamethylenetetramine as a Tool for the Acid-Free Sommelet Reaction in Aqueous Medium

Hexamethylenetetramine (HMTA) is one of the most versatile and most utilized nitrogen-containing heterocyclic compounds in academia and industry. Most of the reactions involving HMTA employ stoichiometric or excess amounts of acid, which hamper the sustainability of the reactions. Herein, we report the first example of the ruthenium-mediated decomposition of HMTA at room temperature, supported by a detailed mechanistic study using thermogravimetric analysis/differential thermal analysis, variable-temperature NMR, UV-vis spectroscopy, and density functional theory techniques. The mechanism study also involves a comparison of the decomposition of HMTA, protonated HMTA, [RuCl3(HMTA)], and [FeCl3(HMTA)], which revealed that [RuCl3(HMTA)] decomposes at the lowest temperature and has the lowest HOMO-LUMO band gap of 2.66 eV. The ruthenium-induced decomposition of HMTA is successfully used as a tool to increase the sustainability of the Sommelet reaction as it employs simple RuCl3·nH2O as a catalyst in as low as 0.5 mol % concentration in aqueous medium. The developed methodology is found to be very selective and efficient even for the very challenging substrates, namely, aliphatic aldehydes and substrates with electron-withdrawing substituents. The findings of this work are the first of its kind in which ruthenium is employed in the Sommelet reaction and also provide a possible platform to improve the sustainability of all reactions involving HMTA as a reactant/reagent.