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Mobile Phase Effects in Reversed-Phase and Hydrophilic Interaction Liquid Chromatography
Published in Nelu Grinberg, Peter W. Carr, Advances in Chromatography Volume 57, 2020
The mobile phase in HILIC systems contains 5–40% water in a polar organic solvent. Protic solvents (lower alcohols) are more similar to water in providing proton donor-acceptor interactions. Consequently, they show lower retention and selectivity in HILIC in comparison to the aprotic acetonitrile, which is the most frequently used organic solvent in HILIC [72].
Elimination Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Common solvents may be organized into two categories: polar or nonpolar, and then protic or aprotic. Apart from being protic or aprotic, an important property of a solvent is polarity, which helps determine the ability of the solvent to solvate and separate ions (solvation). A polar solvent usually has a substantial dipole and a nonpolar solvent tends to have a small dipole, or none at all. A protic solvent is one that contains an acidic hydrogen (O—H, N—H, S—H, essentially a weak Brønsted–Lowry acid), whereas an aprotic solvent does not contain an acidic hydrogen. The essential difference between protic and aprotic solvents is the ability of protic solvents to solvate both cations and anions, whereas aprotic solvents efficiently solvate only cations. Ionization is favored only when both ions are solvated, allowing them to be separated.
Use of Vertically Aligned Carbon Nanotubes for Electrochemical Double-Layer Capacitors
Published in James E. Morris, Krzysztof Iniewski, Nanoelectronic Device Applications Handbook, 2017
Adrianus I. Aria, Mélanie Guittet, Morteza Gharib
According to Equation 35.1, the dielectric constant of the electrolyte is another key component to achieve the high-specific capacitance of EDLCs. Since it is assumed that all ions are in the solvated state, the dielectric constant of the electrolyte is dominated by the dielectric constant of the solvent. Typically, protic solvents such as water, hydrogen cyanide (HCN), and formic acid (FA) have a very high dielectric constant due to the existence of strongly structured hydrogen bonds. On the other hand, aprotic solvents such as propylene carbonate (PC), acetonitrile (ACN), and dimethyl formamide (DMF) typically have a lower dielectric constant than that of the protic solvents, although it is still higher than that of the unstructured solvents due to the presence of strong dipole–dipole interactions. Water, for instance, has a dielectric constant of 80°C at 25°C, while PC has a dielectric constant of 64.
NMR spectral, DFT and antibacterial studies of triazole derivatives
Published in Inorganic and Nano-Metal Chemistry, 2023
S. Mohan, P. Navamani, K. I. Dhanalekshmi, K. Jayamoorthy, N. Srinivasan
In the beginning, the reaction was examined by utilizing divergent catalysts and a multiplicity of solvents for identifies the most favorable conditions to exaggerate the product yield. Then we decided to use Ce-CuO NPs as a catalyst to execute the same reaction under ultrasonic irradiation (Scheme 1). We pinpoint that the yield was only 30% (Table 1). In order to increase the product yield, we use a variety of organic solvents; a massive enhancement was observed in polar protic solvents (60–75%). Then we mixed the water with polar protic solvents and the above reaction was executed; surprisingly, 80–85% of yield was obtained. We further check out the viability of utilizing water as the solvent for this reaction. The result was the same as we expected; under identical conditions, 97% of yield was obtained. Further exploration made known that result was distressed by the variation in the quantity of catalyst. The utmost yield was achieved when 10 mg of catalyst was utilized. Therefore, confidently, our ground-breaking methodology could be a convincing contribution to the existing technology in the field of 1, 4-disubstituted 1, 2, 3-triazole synthesis.
Reactive extraction of lactic and acetic acids from leached bed reactor leachate and process optimization by response surface methodology
Published in Environmental Technology, 2023
Debkumar Chakraborty, Sankar Ganesh Palani, Makarand M. Ghangrekar, Jonathan W.C. Wong
The chemical characteristics of the diluent play a critical role in RE. The diluent's ability to solvate and stabilize the polar ion-pair acid-extractant complex by dipole–dipole interactions or by hydrogen bonding influences the overall extraction performance of the extractant-diluent mixture. Evaluation of these systems revealed that alcohol-based (n-octanol), alkane-based (heptanes) and ester-based (butyl acetate) diluents were typically less performing than the ketone-based (MIBK) diluents. For TOPO and Aliquat 336, the lowest extraction performance was noted for n-octanol. The TOPO's partial dissolution in the aqueous phase makes it less available for carboxylic acid extraction into the organic phase and consistently results in lower extraction yields [17]. Polar-protic solvents, such as octanol, can increase the solubility of dissociable substances. However, this effect is weaker than the previously discussed Van der Waals and electrostatic forces of MIBK. The best lactate extraction results were obtained when MIBK or butyl acetate was used as the diluent and Aliquat 336 was used as the reactant. MIBK is a polar aprotic solvent, and its high dipole moment increases the solubility and extraction efficiency of the lactate anion [42]. Succinic acid extraction yielded similar results due to polar complexes formation between amines and polar aprotic solvents such as methyl isobutyl ketone. These polar complexes form an aggregate to shield themselves from the non-polar environment [44]. Previously, diluents such as oleyl alcohol, chloroform, MIBK, and 1-octanol were tested to increase the solvation power of amine-based extractants, with MIBK being the most effective [16,45]. Based on the above results, preference was given to MIBK and butyl acetate because they generally performed better in the RE experiments for LA. The Aliquat 336 with MIBK and butyl acetate systems shortlisted from the above experiments were used in further studies with varying Aliquat 336-LA concentrations to investigate the influence of time on RE of LA.
Organo-catalytic synthesis of oxathians from isocyanides, isothiocyanates, and oxiranes
Published in Journal of Sulfur Chemistry, 2021
Zahra Keshtegar, Reza Heydari, Alireza Samzadeh-Kermani
We started our study by a reaction involving cyclohexyl isocyanide 1a (1.0 mmol), phenyl isothiocyanate 2a (1.0 mmol), and 2-methyl oxirane 3a (1.0 mmol) in dioxane at 85°C for 18 h. The model reaction did not afford the desired compound 4a, an outcome we attributed to the low nucleophilicity of 1a toward isothiocyanate 2a under the conditions described above. Hou and co-workers have utilized Bu3P as an organo-catalyst to promote ring-opening/cyclization reactions between oxiranes and isothiocyanates. This report encouraged us to examine if Bu3P could mediate our proposed three-component reaction. The reaction conducted with Bu3P in MeCN at 85°C formed 1,3-oxathiolane in 81% yield together with only 7% of the desired product 4a. The model reaction was then performed with 1.5 equiv. of isocyanide 1a (based on 3a), yielding the desired product 4a in 19% yield. During the studies on three-membered heterocycles, we also found that protic solvents could facilitate the ring-opening reaction of such substrates. Based on these findings, the model reaction was conducted with an array of additives and solvents and our selected results are shown in Table 1. Among the organo-phosphine examined (entries 1-4), Bu3P afforded an excellent yield (Table 1, entry 1). Interestingly, electron-rich hetero-aromatic compounds such as N-methyl imidazole (NMI) and N,N-dimethylamino pyridine (DMAP) also promoted the reaction however, the yields were lower than that of Bu3P (Table 1, entries 5-7). Of the solvents (Table 1, entries 1 and 8-16), hexafluoro isopropyl alcohol (HFIP) was selected as the solvent of choice based on the efficiency (entry 1). These studies also revealed that the presence of a protic solvent is necessary to furnish the reaction with good yield. We believe that protic solvents affect the reaction outcome through two possible pathways: (a) protonation of adduct 7 by protic solvents increase the positive charge at the electrophilic carbon of 7, facilitating the subsequent isocyanide’ nucleophilic attack or (b) activation of oxirane toward ring-opening reaction through intramolecular hydrogen-bonding. The former is further supported by the fact that, in contrast to Hou’s work,[21] no oligomerization of phenyl isocyanate was detected under our optimum conditions.