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Alcohols and Phenols as Hydrogen Bonding Catalysts
Published in Andrew M. Harned, Nonnitrogenous Organocatalysis, 2017
Development of more effective catalysts to promote reactions with inherent low reactivity is a major theme in the area of hydrogen bonding catalysis. One strategy to achieve this goal is to use dual hydrogen bond donors to activate a substrate via two-point hydrogen bonding [13]. Another effective strategy that has been frequently employed is to increase the acidity of the hydrogen bond donor by the incorporation of electron-withdrawing groups [36,37]. In this respect, fluorination has been proven to have a positive effect in many cases on the activities of alcohols both as catalysts and reaction solvents due to the increased hydrogen bonding ability of the –OH groups and the decreased nucleophilicity of alcohol oxygens. Indeed, a variety of reactions have been shown to proceed in higher yields and with better selectivities in fluorinated alcohol solvents such as 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) [38–40]. In recent years, fluorinated alcohols started to find widespread use as hydrogen bonding catalysts in a broad range of reactions.
Interfacial Catalysis at Oil/Water Interfaces
Published in Alexander G. Vdlkdv, Interfacial Catalysis, 2002
Since the equilibrium (71a) is shifted to the left, the concentration of OH-anions in the organic phase is thus low, and PTC is only a moderately efficient methodology for β elimination. Nevertheless, there are many examples of successful applications of PTC for practical realization of this process. The effectiveness of PTC for β-elimination reactions becomes much higher when cocatalysts are used. The cocatalysts, mostly alcohols or phenols such as benzyl alcohol, 2,2,2-trifluoroethanol, or mesitol, are deprotonated at the interface and the alkoxide anions produced, introduced into the organic phase by the lipophilic cation of the catalyst, act there as basic agents [80]:
Chemical Analysis
Published in Rudolf Puffr, Vladimír Kubánek, Lactam-Based Polyamides, 2019
Božena Lánská, Jaroslav Stehlíček
The limited solubility of polyamides, especially of polyamide 12, considerably restricts the choice of the solvent. In 1947, Waltz and Taylor112,113 determined carboxylic groups of polyamide 66 in benzyl alcohol solutions; benzyl alcohol has been predominantly used up to this day. Phenol, cresol, a mixture of phenol with benzyl alcohol, propargyl alcohol, chloral hydrate-methanol, and 2,2,2-trifluoroethanol were also used.114-119 In all these solvents polymers dissolve to a limited extent. To reach a concentration in solution, which is necessary for the titrimetric determination, all polymers must be dissolved at temperatures above 100°C. Even so, this means that the titrated solutions have a very low concentration of carboxylic groups, viz., 10–7 mol/ml by order of magnitude. To make the accuracy of determination satisfactory, the solvent must be accordingly pure. Consumption of the titrant by acid impurities in the solvent should not exceed 10% of that by carboxylic groups in the sample; hence, the content of carboxylic groups in the solvent should be below 10–8 mol/ml. For benzyl alcohol, this means that it must be free of benzaldehyde, which is transformed into benzoic acid in an uncontrollable way. A suitable method of purification is seen in the disproportionation of aldehyde into alcohol and acid, which proceeds in an alkaline medium. After purification, benzyl alcohol must be kept under protection of an inert gas, to rule out further possible oxidation. Similarly, all operations of the titrimetric determination must be performed in a stream of inert gas, because otherwise blank consumption by the titration medium has no constant value but increases.
Fabrication and characterization of PVA/CS-PCL/gel multi-scale electrospun scaffold: simulating extracellular matrix for enhanced cellular infiltration and proliferation
Published in Journal of Biomaterials Science, Polymer Edition, 2020
Yong Dou, Xinmeng Fa, Yuanping Gu, Lihua Liang, Jiang Wen, Aimiao Qin, Jun Ou
Poly (vinyl alcohol) (PVA) with 1750 ± 50 degree of polymerization and 98% of degree of hydrolysis and chitosan (CS) were purchased from Sinopharm Chemical Reagent Co., Ltd., China. Polycaprolactone (PCL) (Mn 80,000 g mol−1) and gelatin type A from porcine skin from Sigma (St. Louis, MO) were used throughout this study. Methanol, ethanol, chloroform, sodium chloride salt particles, dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), glutaraldehyde, trifluoroethanol (TFE) and acetic acid of analytical grade were all purchased from Tianjin Chemical Reagent Company. All the chemicals were used without further purification. Mesenchymal stem cells (MSCs) derived from rabbit were obtained from Guilin Medical University. For cell-culture studies, 3-[4,5-dimethylthiazol-2-yl]-diphenyltetrazolium bromide (MTT), Dulbecco’s Modified Eagle’s Medium (DMEM), fetal bovine serum (FBS), penicillin, streptomycin was purchased from Sigma. Sterilized PBS was prepared in the materials laboratory.
Microwave spectrum of the complex of 3,3,3-trifluoro-2-(trifluoromethyl)propanoic acid and formic acid
Published in Molecular Physics, 2019
Javix Thomas, Michael J. Carrillo, Agapito Serrato, Fan Xie, Wolfgang Jäger, Yunjie Xu, Wei Lin
Quantum chemistry calculations were performed using the Gaussian 09 and 16 programme packages [30] at the second-order Møller–Plesset perturbation theory (MP2) [31] and density functional theory (DFT) levels to determine structural parameters and energetic information of the TTPA-FA complex. The Becke three-parameter Lee-Yang-Parr exchange-correlation (B3LYP) functional [32] was implemented for the DFT calculations. In addition, we utilised the combination of B3LYP with D3 dispersion corrections [33] and Becke-Johnson damping [34] since B3LYP-D3BJ has been shown to provide much more accurate structures and energies than without [35]. This has also been demonstrated by rotational spectroscopic studies of hydrogen bonded molecular systems, for example the trifluoroethanol trimer [36]. The results obtained at the B3LYP/aug-cc-pVTZ, B3LYP-D3BJ/def2-TZVP, and MP2/aug-cc-pVTZ levels were used to aid the MW spectroscopic investigation. Single point energy calculations were also performed at the CCSD(T) level to further confirm the conformational stability ordering predicted at the three levels of theory indicated above. In addition, we performed a relaxed one-dimensional potential energy surface scan of the internal rotation of the C(CF3)2H group and also an intrinsic reaction coordinate scan along the double hydrogen tunnelling motion at the B3LYP-D3BJ/def2-TZVP level, utilizing the algorithm developed by Schlegel and co-workers [37–39].
Liquid crystal core polymer fiber mat electronic gas sensors
Published in Liquid Crystals, 2021
Deña Mae Agra-Kooijman, Christina Robb, Yu Guan, Antal Jákli, John L. West
For liquid crystal material, we chose 5CB, because it is a widely used room temperature nematic liquid crystal and because it is stable and has high electric resistivity. 5CB was dispersed in various polymer/solvent solutions, including polyvinyl pyrrolidone (PVP)/ethyl alcohol, PLA/trifluoroethanol (TFE) and cellulose acetate (CA) + polyaniline (PANI)/acetone.