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Synthesis and Characterization of Metal–Organic Frameworks
Published in T. Grant Glover, Bin Mu, Gas Adsorption in Metal-Organic Frameworks, 2018
The second important parameter of MOF synthesis is the solvent because the solubility of the starting materials must be ensured and the selection of the solvent can influence the reaction rate. As a primary component of the reaction mixtures, polar aprotic solvents, such as N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), N,N-dimethylacetamide (DMA), and 1-methyl-2-pyrrolidinone (NMP), are commonly used. In addition to the high solubility of metal salts, it is known that these solvents are partially decomposed through the solvothermal reaction. The generated amine species (e.g., dimethylamine) can facilitate the deprotonation of organic linkers, leading to the formation of a strong bond between the metal ion and the deprotonated linker terminal (e.g., carboxylate and imidazolate). To facilitate the linker deprotonation, basic additives, such as triethylamine and sodium hydroxide, can also be used. Indeed, the addition of base enables the room temperature MOF synthesis.16 It is not always necessary to purify these solvents as long as the target materials are obtained with reasonable reproducibility. Similarly, regular solvents (not dried solvents) can be used when hydrated metal salts are used for the MOF synthesis. However, if the reproducibility and/or crystallinity of MOF materials are poor, the reasons could be related to the purity of the solvents and other starting materials.
Theoretical Consideration Of Solubility
Published in A. L. Horvath, Halogenated Hydrocarbons, 2020
The interaction between the solute and solvent molecules are of several types, such as: Electrostatic (dipole-dipole and ion-dipole)Dispersion forcesDonor-acceptorHydrogen bondingStructure breakingStructure making The nature of solute-solvent interaction is responsible, for example, for the solvation of reactants and the transition state. Furthermore, in nucleophilic reactions there is hydrogen bonding between a protonic solvent and the nucleophile (e.g., alcohols and water). When the nucleophile is uncharged, the hydrogen bonding is weak. The nucleophilic strength of carbon for halide ions in water or alcohols has been studied by Parker (1962), Alexander et al. (1968), and Bunnett (1963). They found that the order of nucleophilic strength is Cl< Br<I in alcohols or water and the reverse in aprotic solvents. In protonic solvents, the hydrogen-bonding solvation is stronger for small nucleophiles. Solvents with dielectric constants greater than 15 (i.e., polar aprotic solvents) are capable of promoting nucleophilic reactions. The hydrocarbons, CC14, and so on are nonpolar aprotic solvents.
Refining of Indian coals to obtain super clean coals having insignificant amounts of deleterious elements under milder conditions
Published in Mineral Processing and Extractive Metallurgy, 2021
All raw coal samples showed good amounts of major and trace elements due to the presence of ash (Table 5). Although, Pandra and Bahula coals being high ash coals reported higher concentrations as compared to low ash coals, Bhagabandh, Moonidih and Neyveli lignite as the case may be. All SCCs showed less amounts of major and trace elements as compared to their raw coal samples as greater than 93% ash reduction could be achieved for all coals. This verifies the ability of NMP which is a polar aprotic solvent to show good coal extracting properties in cooperation with the smaller amount of co-solvent EDA (Pande and Sharma 2002). Renganathan et al. (Renganathan et al. 1988) used NMP and reported the non-destructive extraction yield of 37–75% of three bituminous coals obtaining a clean solid product having less than 0.2% ash. The major and the trace elements that were still present in the SCCs show the strong association with the organic matrix of coal. However, the synergistic effect of EDA with NMP results in the recovery of SCCs from coals by breaking the association of most of the mineral matter contents with the three dimensional cross linked gel network coal structure. Therefore organo-refining by e,N results in the significant separation of major and trace elements from the organic matter in these coals thereby producing clean products (i.e. SCCs) (Wang et al. 2004).
DFT study on coupling reaction of carbon dioxide with ethylene oxide catalyzed by 1,4,6-triaza-bicyclo[3.3.0]oct-4-enium bromide (TBO.HBr)
Published in Molecular Physics, 2020
Abdudin Geremu Temam, Teshome Abute Lelisho
All inputs in this inquiry were constructed by using Gauss view 5.0.9 and all quantum calculations were performed by Gaussian 09 [40] software package. Preliminarily semi-empirical calculations were carried out by PM6 [41] model to determine the most stable conformations of all equilibrium structures. After obtaining the needed conformation, all calculations were carried out by DFT [42] method using B3LYP [43,44] functional in combination with 6-31G(d,p) basis set [45] without any symmetry constraint. Vibrational frequency calculations were performed to check whether the obtained equilibrium structures are local minima or saddle points. All reactants, intermediates and products possess real frequencies, while all transition states possess only one imaginary frequency. Thermochemical data were obtained from vibrational frequencies calculations. The calculated activation barrier is the respective energy difference between the transition state and reactant complex or intermediate. Synchronous Transit-Guided Quasi-Newton method developed by Schlegel [46]) was used to locate transition states between the two minima. Intrinsic reaction coordinate (IRC) [47] calculations were performed to confirm the optimised transition states connecting the desired minima’s on the reaction coordinates. The effect of polar protic solvent (water) and polar aprotic solvent tetrahydrofuran (THF) was considered by standard polarisable continuum model (PCM) [48] developed by Tomasi’s group in the framework of SCRF.
A DFT study on the addition and abstraction reactions of thiourea with hydroxyl radical
Published in Journal of Sulfur Chemistry, 2018
Mwadham. M. Kabanda, Kemoabetswe R. N. Serobatse
Another factor that measures the effectiveness of the antioxidant radical scavenging species, when acting through H atom abstraction, is the N–H BDE, which can be estimated following the equation where H (TU•) is the enthalpy of the radical generated by H atom abstraction, H (H•) is the enthalpy of the H atom, and H (TU) is the enthalpy of the parent molecule (i.e. optimized TU conformer). The results of the study show that the N–H BDE (kcal/mol) for TU has a value of 101.698 (102.063 with the DFT/M06–2X method and 100.107 with the DFT/BHHLYP method) in vacuo and a value of 106.561 (107.528 with the DFT/M06–2X method and 105.711 with the DFT/BHHLYP method) in water solution. These values are slightly higher than the experimentally determined value of 93 kcal/mol for the N–H BDE in TU, obtained in dimethyl sulfoxide solution [78]. The N–H bond dissociation in TU is therefore easier in polar aprotic solvent than in polar solvent. Moreover, the experimental value of 93 kcal/mol for the BDE of the N–H bond in TU is higher than the experimental value of 88.3 ± 0.8 kcal/mol for the O–H bond dissociation in phenol [79], indicating that phenol derivatives may be better radical scavengers than TU derivatives.