Theoretical and Experimental Studies on the Regioselectivity of Epoxide Ring Opening by Nucleophiles in Nitromethane without any Catalyst: Nucleophilic-Chain Attack Mechanism

Porous Coordination Polymer MOF-808 as an Effective Catalyst to Enhance Sustainable Chemical Processes

The improvement of sustainable chemical processes plays a pivotal role in safe environmental and societal development, for example, by reducing the use of hazardous substances, preventing chemical waste, and improving the efficiency of chemical reactions to obtain added-value compounds. In this context, the porous coordination polymer MOF-808 (MOF, metal-organic framework) was prepared by a straightforward method in water, at room temperature, and was unequivocally characterized by powder X-ray diffraction, vibrational spectroscopy, thermogravimetric analysis, and scanning electron microscopy. MOF-808 material was applied for the first time as catalysts in ring-opening aminolysis reactions of epoxides. It demonstrated high activity and selectivity for reactions of styrene oxide and cyclohexene oxide with aniline, using a very low amount of an eco-sustainable solvent (0.5 mL of EtOH), at 70 °C. Moreover, MOF-808 demonstrated high stability in the catalytic reaction conditions applied, and a notable reuse capacity of up to 20 consecutive reaction cycles, without significant variation in its catalytic performance. In fact, this Zr-based porous coordination polymer prepared by environment-friendly conditions proved to be a novel efficient heterogeneous catalyst, promoting the ring-opening reaction of epoxides under more sustainable conditions, and using a very low amount of catalyst.

Reaction mechanism of the green synthesis of glutaric acid

In this study, the reaction mechanism underlying the green synthesis of glutaric acid was studied via joint test technology. Density functional theory calculations were used to verify the mechanism. Quantitative analysis of glutaric acid via infrared spectroscopy and HPLC was established. The linear correlation between the two methods was good, from 0.01 to 0.25 g mL^-1. The analysis results of the two methods were consistent as the reaction progressed.

Experimental and Computational Studies of Microwave-Assisted, Facile Ring Opening of Epoxide with Less Reactive Aromatic Amines in Nitromethane

Nucleophilic ring opening reactions of epoxides with aromatic amines are in the forefront of the synthetic organic chemistry research to build new bioactive scaffolds. Here, convenient, green, and highly efficient regioselective ring opening reactions of sterically hindered (2R,3S)-3-(N-Boc-amino)-1-oxirane-4-phenylbutane with various poorly reactive aromatic amines are accomplished under microwave irradiation in nitromethane. All the reactions effectively implemented for various aromatic amines involve the reuse of nitromethane that supports its dual role as a solvent and catalyst. The corresponding new β-alcohol analogs of hydroxyethylamine (HEA) are isolated in 41-98% yields. The reactions proceed under mild conditions for a broad range of less reactive and sterically hindered aromatic amines. Proton NMR experiments suggest that the nucleophilicity of amines is influenced by nitromethane, which is substantiated by the extensive computational studies. Overall, this methodology elucidates the first-time use of nitromethane as a solvent for the ring opening reactions under microwave conditions involving an equimolar ratio of epoxide and aromatic amine without any catalyst, facile ring opening of complex epoxide by less reactive aromatic amines, low reaction time, less energy consumption, recycling of the solvent, and simple workup procedures.

M-Type SrFe12O19 Ferrite: An Efficient Catalyst for the Synthesis of Amino Alcohols under Solvent-Free Conditions

Magnetically separable strontium hexaferrite SrFe12O19 was prepared using the chemical coprecipitation method, and the nanostructured material was characterized by X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and BET analysis. The SEM images showed the homogeneity of the chemical composition of SrFe12O19 and uniform distribution of size and morphology. The pore size of the nanomaterial and its specific area were determined by BET measurements. Strontium hexaferrite SrFe12O19 exhibited a strong magnetic field, which is highly suitable in the heterogeneous catalysis as it can be efficiently separated from the reaction. The magnetic nanocatalyst showed high activity and environmentally benign heterogeneous catalysts for the epoxide ring-opening with amines affording β-amino alcohols under solvent-free conditions. When unsymmetrical epoxides were treated in the presence of aromatics amines, the regioselectivity was influenced by the electronic and steric factors. Total regioselectivity was observed for the reactions performed with aliphatic amines. The magnetically SrFe12O19 nanocatalyst showed excellent recyclability with continuously good catalytic activities after four cycles.

Behaviour Modelling of Organic Bases in the Oxyalkylation Reaction of Proton-Containing Nucleophiles

The mechanism of action of nucleophilic and non-nucleophilic bases in the system “acetic acid (HOAc) – epichlorohydrin (ECH) – R3X (R = alkyl, X = N, P)” has been studied. The observed orders of the reaction with respect to the components were found. It has been proved that the catalytic activity of the starting bases is determined by their nucleophilicity, rather than basicity. It is shown that the crucial stage of the reaction is the quaternisation of the starting base with the formation of a reactive intermediate, the acetate anion. Monitoring of possible paths of oxirane ring-opening by the initial base and the acetate anion was carried out. The behaviour of the model base, triphenylphosphine, in the quaternisation reaction was studied by UV spectroscopy. The rate constants of quaternisation in the reaction of tribenzylamine and triphenylphosphine with ECH have been estimated. The activation parameters of the stages of oxirane ring-opening by trimethylamine and the acetate anion were calculated using a quantum chemical method. It has been shown that the starting base attacks only the activated oxirane, while the acetate anion is capable of nucleophilic opening of both activated and non-activated ECH rings. A scheme for the catalytic opening of the oxirane ring by the bases in the system “ECH – HOAc – R3X” is proposed, which includes a series of both consecutive and parallel stages leading to the formation of the reaction product.

Quantum Mechanical Study of γ-Fe2O3 Nanoparticle as a Nanocarrier for Anticancer Drug Delivery

Using density functional theory (DFT), noncovalent interactions and four mechanisms of covalent functionalization of melphalan anticancer drug onto γ-Fe2O3 nanoparticles have been studied. Quantum molecular descriptors of noncovalent configurations were investigated. It was specified that binding of melphalan onto γ-Fe2O3 nanoparticles is thermodynamically suitable. Hardness and the gap of energy between LUMO and HOMO of melphalan are higher than the noncovalent configurations, showing the reactivity of drug increases in the presence of γ-Fe2O3 nanoparticles. Melphalan can bond to γ-Fe2O3 nanoparticles through NH2 (k 1 mechanism), OH (k 2 mechanism), C=O (k 3 mechanism) and Cl (k 4 mechanism) groups. The activation energies, the activation enthalpies and the activation Gibbs free energies of these reactions were calculated. Thermodynamic data indicate that k 3 mechanism is exothermic and spontaneous and can take place at room temperature. These results could be generalized to other similar drugs.

Theoretical Study on the Mechanism of Covalent Bonding of Dapsone onto Functionalised Carbon Nanotubes: Effects of Coupling Agent

Using density functional theory, two mechanisms of covalent bonding of dapsone onto functionalised carbon nanotubes have been investigated, the first one being direct bonding and the second one being bonding by using coupling agents. In this work, the mechanism of functioning of an important coupling agent (1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo [4,5-b]pyridinium 3-oxide hexafluorophosphate, N-HATU) has been investigated. The activation energy and activation Gibbs free energy of the two pathways have been calculated and compared with each other. It was found that using the coupling agents will reduce the energy barrier. All of the calculations have been performed in the solution phase (polarised continuum model) using the B3YLP hybrid density functional.

Mechanism of covalent adsorption of benzenesulfonamide onto COOH– and COCl– functionalised carbon nanotubes

Using density functional theory, two mechanisms of covalent adsorption of benzenesulfonamide in water in the presence of functionalised carbon nanotubes were investigated. COOH– and COCl–functionalised carbon nanotubes can bond to the benzenesulfonamide via OH (OH pathway) and Cl (Cl pathway) groups, respectively. The activation energy and activation Gibbs free energy of the two pathways have been calculated and compared with each other. It was found that the OH pathway has an energy barrier higher than the Cl pathway and, in contrast to the Cl pathway, product formation is endothermic and non-spontaneous, being thus the reason for the dominance of the Cl pathway. All the calculations were performed using a hybrid density functional method (B3LYP) in the solution phase (polarised continuum model or PCM).

Quantum mechanical study on the different fluxional mechanisms in a [Pd(η2-olefin) complex

In this work, using quantum mechanics, different fluxional mechanisms in a Pd(η2-olefin) complex including sulfur inversion, olefin pseudo rotation, Pd–olefin bond dissociation, propeller-like olefin rotation and a bimolecular process have been investigated theoretically in a solvent environment using the polarisable continuum model (PCM). The activation energy, activation enthalpy and activation Gibbs free energy of the different pathways have been calculated and compared with each other and with experimental results. These activation energies for olefin pseudo rotation, Pd–olefin bond dissociation and propeller-like olefin rotation are greater in comparison with those for the sulfur inversion and bimolecular process, which demonstrates that these latter mechanisms are the dominating paths and make the main contributions in the reaction. The computed activation enthalpies of the sulfur inversion and bimolecular process pathways are in good agreement with the experimental values. All of the calculations have been performed using a hybrid density functional method (B3LYP) in the solution phase.

Density Functional Theoretical Study on the Mechanism of Adsorption of 2-Chlorophenol from Water Using γ-Fe2O3 Nanoparticles

Using density functional theory, the mechanism of adsorption of 2-chlorophenol from water in the presence of γ-Fe2O3 nanoparticles was investigated. Fe2O3 nanoparticles were modelled using Fe6(OH)18(H2O)6 ring clusters. 2-chlorophenol can coordinate to the γ-Fe2O3 nanoparticles via its own OH or Cl groups. The process produces two intermediates which will be converted into final products through two pathways (Cl pathway and OH pathway). The activation energy and activation Gibbs free energy of the two pathways have been calculated and compared with each other. It was found that the OH pathway is under thermodynamic control and the C1 pathway is under kinetic control. All of the calculations were performed using a hybrid density functional method (B3LYP) in the solution phase (PCM model).