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201.
Intermolecular additions of the O-H bonds of phenols and alcohols and the N-H bonds of sulfonamides and benzamide to olefins catalyzed by 1 mol % of triflic acid and studies to define the relationship between these reactions and those catalyzed by metal triflates are reported. Cyclization of an alcohol containing pendant monosubstituted and trisubstituted olefins catalyzed by either triflic acid or metal triflates form products from addition to the more substituted olefin, and additions of tosylamide catalyzed by triflic acid or metal triflates form indistinguishable ratios of the two N-alkyl sulfonamides. 相似文献
202.
Enabling Suzuki–Miyaura coupling of Lewis-basic arylboronic esters with a nonprecious metal catalyst
Michael C. Haibach Andrew R. Ickes Sergei Tcyrulnikov Shashank Shekhar Sebastien Monfette Rafal Swiatowiec Brian J. Kotecki Jason Wang Amanda L. Wall Rodger F. Henry Eric C. Hansen 《Chemical science》2022,13(43):12906
The high cost and negative environmental impact of precious metal catalysts has led to increased demand for nonprecious alternatives for widely practiced reactions such as the Suzuki–Miyaura coupling (SMC). Ni-catalyzed versions of this reaction have failed to achieve high reactivity with Lewis-basic arylboron nucleophiles, especially pinacolboron esters. We describe the development of (PPh2Me)2NiCl2 as an inexpensive and air-stable precatalyst that addresses this challenge. Under activation by n-BuMgCl, this complex can catalyze the coupling of synthetically important heteroaryl pinacolborons with heteroaryl halides. Mildly basic conditions (aqueous K3PO4) allow the reaction to tolerate sensitive functional groups that were incompatible with other Ni-SMC methods. Experimental and computational studies suggest that catalyst inhibition by substitution of PPh2Me from Ni(ii) intermediates by Lewis basic reactants and products is disfavored relative to more commonly employed ligands in the Ni-SMC, which allows it to operate efficiently in the presence of Lewis bases such as unhindered pyridines.A simple inexpensive ligand enables the Ni-catalyzed Suzuki–Miyaura coupling of heterocyclic and Lewis-basic arylboronic esters under mild conditions. 相似文献
203.
Journal of Radioanalytical and Nuclear Chemistry - Solvent extraction of Cs(I) and Sr(II) from a simulated radwaste acidic solution was studied with chlorinated cobalt dicarbollide/polyethylene... 相似文献
204.
Chandra Shekhar Tiwari Praseetha Mathoor Illam S. N. R. Donthireddy Dr. Arnab Rit 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(67):16581-16600
In the past few decades, chemistry of cyclometalated species has gained momentum with increased applications in several areas of scientific developments. Cyclometalation reactions result in the formation of stable metallacycles through the generation of metal-carbon covalent bonds by activating the unreactive Csp2-H or Csp3-H bonds. The extra stability gained by the formation of metallacycles enhances their applicability scopes especially in the area of homogeneous catalysis. In the recent research development in this area, NHC ligands (strong σ-donor and generally, weak π-acceptor) have been found to be one of the most suitable candidates for the intramolecular C−H activation process which leads to the cyclometalated species. The growth in the area of cyclometalation chemistry that started in the late 20th century is still continuing and in the past few decades, various examples of NHC derived transition metal-based cyclometalated complexes came into the picture. As covering all the reported literatures in this area (includes mainly late transition metals) will exceed the limits of minireview, we restricted ourselves to the recent (2015 – May 2021) examples of the most common Ru-, Rh-, and Ir-based CNHC^C cyclometalated complexes and their applications in various homogeneous catalytic conversions such as transfer hydrogenation, amidation, oxidation of alcohols, annulations, and so forth. 相似文献
205.
The phase diagrams of binary organic faceted-faceted systems of p-dibromobenzene with acenaphthene, p-chloronitrobenzene and acetanilide show the formation of a simple eutectic with 0.53, 0.61, and 0.64 mole fraction of p-dibromobenzene, respectively. Crystallization data, determined by the capillary method, suggest that the eutectics of p-dibromobenzene with acenaphthene and p-chloronitrobenzene solidify with alternate nucleation mechanism and the crystallization of the eutectic of p-dibromobenzene-acetanilide system takes place by the side-by-side growth of the phases involved. With a view to throw light on the thermodynamic behaviour of eutectic alloys of non-metals, heats of fusion of their transparent organic analogues and their eutectics were determined, and using these values different thermodynamic parameters were calculated. The microstructures of the eutectics show their typical characteristic features. 相似文献
206.
In the present study, poly(N-Isopropylacrylacrylamide-co-N-tertiarybutylacrylamide-co-hydroxyethylcrylamide) (NIPAM-co-NTBA-co-HEAAm) hydrogels are prepared with variation of molar ratio of hydrophilic HEAAm and hydrophobic NTBA. The prepared hydrogels are characterized with elemental analysis and Fourier transform infrared (FTIR) spectroscopy. The thermodynamics of swelling properties of poly(NIPAM-co-NTBA-co-HEAAm) hydrogels have also been discussed. The experimental C/N ratios are comparable with the theoretical value. The enthalpy change of mixing ∆Hmix, entropy change of mixing ∆Smix, free energy change of mixing ∆Gmix are determined for swelling of hydrogels at 25 °C. The value of total free energy of hydrogel swelling is found to be negative which confirms the lower critical solution temperature (LCST) exhibited in all hydrogels and the volume change transition shows the thermoresponsive behavior. The values of ∆Smix increase and ∆Gmix decrease with increasing amount of hydrophobic NTBA content in the hydrogels. The values of free energy change of elasticity (∆Gel) are found to be increased with increasing the hydrophobic NTBA content followed by decrease in swelling percentage. Also, the transition temperature of the hydrogel is found to be decreased with increasing the hydrophobic NTBA. 相似文献
207.
Varun Kumar Sing Souvik Sur Mohd. Musharraf Ratan Kumar Dey Sanjay Kumar Swain Suman Shekhar 《Macromolecular Symposia》2024,413(1):2300045
In the present study, the degradation process of piperazine (PP) immobilized silica gel (SiPP) is investigated under dynamic conditions. The degradation of SiPP is studied with thermogravimetric analyzer (TGA). The kinetics of degradation process is analyzed by Kissinger method, Flynn–Wall–Ozawa's (FWO) method, and Deconvolution method. It is found that degradation of SiPP can be described by parallel independent two-portion process model, which includes two processing state of the system (marked by processes 1 and 2), where process 1 and 2 can be attributed to decomposition processes of organic moiety attached on silica surface. The apparent activation energy (Ea) is calculated by Flynn–Wall–Ozawa's (FWO) method and deconvolution method. 相似文献