High regioselectivity in the amination reaction of isoquinolinequinone derivatives using conceptual DFT and NCI analysis

Reaction Pathway Analysis of PET Deconstruction via Methanolysis and Tertiary Amine Catalysts

Polyethylene terephthalate (PET) is a type of polymer frequently used in plastic packaging that significantly adds the amount of plastic waste found in landfills. One of the ways to recover valuable raw materials from postconsumer plastic is by depolymerizing PET into its monomeric constituents, which are dimethyl terephthalate (DMT) and ethylene glycol. PET depolymerization is often done in methanolysis with the help of acidic or base catalysts. Tertiary amine is one of the most attractive base catalysts for PET depolymerization in methanolysis since it does not lead to the generation of potentially environmentally harmful waste, unlike metal-based catalysts. However, the mechanism by which tertiary amines catalyze PET depolymerization in methanolysis remains unexplored. Developing a detailed mechanistic understanding of this process is important for improving plastic upcycling since it opens the possibility of employing various cheaper and more environmentally friendly reaction conditions. Using density functional theory and transition state analysis, we show that in the presence of tertiary amine catalysts, methanolysis of PET consists of multiple discrete-step reactions rather than a single concerted step. Furthermore, by comparing our calculations to recent experimental results, we were able to rationalize the DMT yield from the depolymerization process by relating it to charge polarization within tertiary amine catalysts, thus opening a pathway to identify atomic descriptors for future catalyst design.

Exploring the Sensing Potential of g-C3N4 versus Li/g-C3N4 Nanoflakes toward Hazardous Organic Volatiles: A DFT Simulation Study

Ab initio calculations were performed to determine the sensing behavior of g-C3N4 and Li metal-doped g-C3N4 (Li/g-C3N4) quantum dots toward toxic compounds acetamide (AA), benzamide (BA), and their thio-analogues, namely, thioacetamide (TAA) and thiobenzamide (TAA). For optimization and interaction energies, the ωB97XD/6-31G(d,p) level of theory was used. Interaction energies (Eint) illustrate the high thermodynamic stabilities of the designed complexes due to the presence of the noncovalent interactions. The presence of electrostatic forces in some complexes is also observed. The observed trend of Eint in g-C3N4 complexes was BA > TAA > AA > TBA, while in Li/g-C3N4, the trend was BA > AA > TBA > TAA. The electronic properties were studied by frontier molecular orbital (FMO) and natural bond orbital analyses. According to FMO, lithium metal doping greatly enhanced the conductivity of the complexes by generating new HOMOs near the Fermi level. A significant amount of charge transfer was also observed in complexes, reflecting the increase in charge conductivity. NCI and QTAIM analyses evidenced the presence of significant noncovalent dispersion and electrostatic forces in Li/g-C3N4 and respective complexes. Charge decomposition analysis gave an idea of the transfer of charge density between quantum dots and analytes. Finally, TD-DFT explained the optical behavior of the reported complexes. The findings of this study suggested that both bare g-C3N4 and Li/g-C3N4 can effectively be used as atmospheric sensors having excellent adsorbing properties toward toxic analytes.

Theoretical Investigation of Regiodivergent Addition of Anilines and Phenolates to p-Benzoquinone Ring

Two different products were obtained by the regiodivergent reaction of benzoquinone derivatives with phenolates and anilines: 3-aryloxybenzoquinone and 2-phenylamino-3-bromobenzoquinone. Calculated density functional theory free energies of reaction values corroborate the experimental observation of the formation of the substitution product in the reaction with phenolates in acetonitrile and the product of addition/oxidation for the reaction with aniline in water. Calculated charges and Fukui functions are similar for C2 and C3 atoms, indicating an equal possibility to suffer a nucleophilic attack. The calculated energy barriers for nucleophilic attack steps indicated that the first steps of the substitution with phenolates and addition/oxidation with anilines are faster, which justifies the formation of the respective products. The natural bond order analysis for the transition states revealed that there is a strong interaction between lone pairs of N and O atoms and the π_C2C3 ^* for the O → C2 and N → C3 attacks and a weak interaction for the O → C3 and N → C2 attacks, which also agrees with experimental observations.