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All total 244 Articles be found
All total 244 Articles be foundRelation of the Transition-State Structure for the Water-Catalyzed Hydrolysis of 1-Acetylimidazolium Ion to Solvent Hydrophobicity: Proton Inventories in Water-Acetonitrile Mixtures
Huskey, William P.,Hogg, John L.
, p. 53 - 59 (1981)
The transition-state structure for the water-catalyzed hydrolysis of 1-acetylimidazolium ion has been probed in solvent systems which may mimic the hydrophobic nature of an enzyme's active site.The kinetic solvent deuterium isotope effect kH2O/kD2O, are 2.58, 2.49, and 2.10 in water, in 0.5 vol fraction of acetonitrile in water, and in 0.9 vol fraction of acetonitrile in water, respectively.The proton inventory investigations suggest all three solvent system entertain a transition-state structure composed of a catalytic proton bridge between the reorganizing substrate and a water molecule acting as a general base-catalyst.A "compression" of the transition-state structure in the solvent system containing the largest amount of acetonitrile is suggested to be responsible for the diminished kinetic solvent deuterium isotope effect.The reaction has been shown to be second order with respect to water.
Catalysis of the methanolysis of acetylimidazole by lanthanum triflate
Neverov, Alexei A.,Brown
, p. 1247 - 1250 (2000)
Methanolysis of acetylimidazole (1) and N-acetylimidazolepentamine-Co(III) (2) was found to be markedly accelerated in the presence of La(OTf)3. Potentiometric titration of a solution of La3+(OTf-)3 gave a pKa for the metal bound CH3OH of 7.22. The kinetics of methanolysis of 1 and 2 were measured at 25°C at various pH under buffered conditions as a function of increasing La3+. Analysis of both the kinetic and potentiometric data indicates that the catalytically active species is a La3+-dimer, bridged by two methoxides, (CH3OH)nLa3+(CH3O-) 2La3+(CH3OH)n. The maximum second-order rate constants for attack of the dimer on 1 and 2 are 1.50 × 103 M-1 s-1 and 1.42 × 102 M-1 s-1 respectively and both processes adhere to titration of a La3+(CH3OH) to generate the active form. The results are explained in terms of a mechanism where the methoxy-bridged La3+ dimer transiently breaks a La3+-OCH3 bond to expose both a CH3O- nucleophile and a La3+ which can act as a Lewis acid. Unlike the situation in water, the methanol results indicate that the medium greatly stabilizes and solubilizes the active dimer without the necessity of creating specially designed ligands to stabilize the dinuclear core.
The stability of N, N -carbonyldiimidazole toward atmospheric moisture
Engstrom, Kenneth M.,Sheikh, Ahmad,Ho, Raimundo,Miller, Robert W.
, p. 488 - 494 (2014)
N,N-Carbonyldiimidazole (CDI) is known to be sensitive to degradation by atmospheric moisture. This work details some mechanistic aspects of CDI degradation by atmospheric moisture along with the major contributing factors to degradation rate. Also, several analytical techniques for the measurement of CDI purity that are less cumbersome than the traditional gas-capture assay are described.
Development of a method for the quantification of clotrimazole and itraconazole and study of their stability in a new microemulsion for the treatment of sporotrichosis
Ferreira, Patricia Garcia,de Souza Lima, Carolina Guimar?es,Noronha, Letícia Lorena,de Moraes, Marcela Cristina,de Carvalho da Silva, Fernando,Vi?osa, Alessandra Lifsitch,Futuro, Débora Omena,Ferreira, Vitor Francisco
, (2019)
Sporotrichosis occurs worldwide and is caused by the fungus Sporothrix brasiliensis. This agent has a high zoonotic potential and is transmitted mainly by bites and scratches from infected felines. A new association between the drugs clotrimazole and itraconazole is shown to be effective against S. brasiliensis yeasts. This association was formulated as a microemulsion containing benzyl alcohol as oil, Tween 60 and propylene glycol as surfactant and cosurfactant, respectively, and water. Initially, the compatibility between clotrimazole and itraconazole was studied using differential scanning calorimetry (DSC), thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FTIR), and X-ray powder diffraction (PXRD). Additionally, a simple and efficient analytical HPLC method was developed to simultaneously determine the concentration of clotrimazole and itraconazole in the novel microemulsion. The developed method proved to be efficient, robust, and reproducible for both components of the microemulsion. We also performed an accelerated stability study of this formulation, and the developed analytical method was applied to monitor the content of active ingredients. Interestingly, these investigations led to the detection of a known clotrimazole degradation product whose structure was confirmed using NMR and HRMS, as well as a possible interaction between itraconazole and benzyl alcohol.
EFFECT OF THE SURFACE AREA OF PLATINUM ON THE ACTIVITY OF A BIFUNCTIONAL ALUMINOPLATINUM CATALYST IN THE SYNTHESIS OF ALKYLIMIDAZOLES FROM DIAMINES AND CARBONYL ACIDS
Gitis, K. M.,Raevskaya, N. I.,Zaitsev, A. V.,Borovkov, V. Yu.,Kozan, S. B.,Isagulyants, G. V.
, p. 1547 - 1550 (1992)
An investigation has been conducted into the effect of the acid and dehydrogenating functions of an aluminoplatinum catalyst on the synthesis of 2-methylimidazole from ethylenediamine and acetic acid.It has been established that formation of the intermediate 2-methylimidazoline involves the acid Al2O3 centers and its rate of formation is greater than the rate of its subsequent dehydrogenation to 2-methylimidazole on the Pt centers.The symbatic nature of the variations in the 2-methylimidazole yield and the surface area of the platinum in the aluminoplatinum catalyst has been demonstrated.Keywords: C-alkylimidazoles, 2-methylimidazole, aluminoplatinum catalyst.
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Shulman,Simmonds
, p. 1040 (1968)
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Method for protecting sulfonyl of deamination amine
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Paragraph 0048-0050, (2021/11/03)
The invention discloses a method for removing sulfenyl protection of amine. The method comprises the following steps: dissolving N - sulfonyl-protected amine and a base in a reaction solvent, then adding diphenylphosphine to uniformly mix and maintain 90 °C. When TCL detection reaction is complete, a recrystallization method or an extraction separation method is adopted to obtain the target product. The method disclosed by the invention adopts diphenylphosphine as an extraction reagent, is good in reaction activity, high in selectivity and wide in application range, and can replace the use of a hazardous reagent under the basic heating condition. Prodrug research and development and industrial production are of great significance.
Indirect reduction of CO2and recycling of polymers by manganese-catalyzed transfer hydrogenation of amides, carbamates, urea derivatives, and polyurethanes
Liu, Xin,Werner, Thomas
, p. 10590 - 10597 (2021/08/20)
The reduction of polar bonds, in particular carbonyl groups, is of fundamental importance in organic chemistry and biology. Herein, we report a manganese pincer complex as a versatile catalyst for the transfer hydrogenation of amides, carbamates, urea derivatives, and even polyurethanes leading to the corresponding alcohols, amines, and methanol as products. Since these compound classes can be prepared using CO2as a C1 building block the reported reaction represents an approach to the indirect reduction of CO2. Notably, these are the first examples on the reduction of carbamates and urea derivatives as well as on the C-N bond cleavage in amides by transfer hydrogenation. The general applicability of this methodology is highlighted by the successful reduction of 12 urea derivatives, 26 carbamates and 11 amides. The corresponding amines, alcohols and methanol were obtained in good to excellent yields up to 97%. Furthermore, polyurethanes were successfully converted which represents a viable strategy towards a circular economy. Based on control experiments and the observed intermediates a feasible mechanism is proposed.
