Search Results
Abstract
A study was made of the influence of the chemical structure of the chains on the thermal stability of a series of copolyethers obtained from 3,3-bis(chloromethyl)oxetane and various bisphenols: 4,4'-dihydroxyazobenzene, 4,4'-dihydroxydiphenyl, 4,4'-thiodiphenol, 1,1-bis(4-hydroxy-phenyl)ethane and 4,4'-dihydroxydiphenylsulfone. For a better correlation between chemical structure and thermal stability, molecular simulations were performed, using the HYPERCHEM (version 4.5) program. The lowest thermal stability was exhibited by the polymers that contain azobenzene units. The best thermal stability was that of the polyethers containing thiodiphenyl and 1,1-bis(phenyl)ethane units.
Abstract
Using mild conditions and short reaction times, symmetrical disulfides have been synthesized in flow chemistry using phase transfer catalysts to facilitate the substitution of organohalides with disodium disulfide. Also, the synthesis of symmetrical trisulfides was possible using this procedure with an additional equivalent of sulfur.
Abstract
O-Alkylation of phenol compounds was performed in a continuous flow apparatus under biphasic liquid/liquid conditions and promoted by tetrabutylammonium bromide (TBAB) as a phase-transfer catalyst. The segmented flow that is generated within the flow system is able to afford the desired ethers in high yield and in very short times.
Herein, we illustrate how microreactor technology can be used as a tool for reaction screening and optimization, in addition to improving the reaction chemistry. We report the in-situ generation of azo compounds by reactive quenching of diazonium intermediates in microreactors. This involves an electrophilic aromatic substitution reaction, namely, an azo-coupling reaction performed in continuous-flow systems in the presence of a phase transfer catalyst with great emphasis on compounds that do not easily couple. Capitalizing on the benefits of a large surface area and the short molecular diffusion distances observed in microreactors, in-situ phase transfer catalyzed azo-coupling reaction of diphenylamine to p-nitroaniline was investigated. A rapid and easy optimization protocol was established which yielded a 99%, 22%, and 33% conversion of diphenylamine, carbazole, and triphenylamine, respectively, in approximately 2.4 min.
Abstract
Catalytic phenomena in solvent extraction of metals with hydrophobic chelating extractants are reviewed. Interface modification by adsorption of additives, phase transfer catalysis, formation of micelles, reversed micelles and microemuslions are discussed and examples are given.
Abstract
The paper presents a thermogravimetric study of some aromatic poly- and copolyethers, using mass spectrometry technique combined with thermogravimetric analysis. The polymers were synthesized by phase transfer catalysis technique, using bis(2-chloroethyl)-ether or 1,6-dichlorohexane as flexible spacers and various bisphenols (4,4'-dihydroxydiphenyl, 4,4'-dihydroxyazobenzene and bisphenol A). The presence of azobenzenic moieties in the chain induces a liquid crystalline behavior, but, due to the high values of the transition temperature, some precautions during the thermal characterisation are necessary. In the case of azobenzenic samples, the degradation reactions begin, as a function of the chemical structure, around 230-250C. A degradation mechanism based on chain transfer reactions was proposed. The chain flexibility influences the thermal degradation mechanism, in the case of rigid polymers the chain transfer reactions being less probable. For the flexible chains, the thermal stability is not essentially influenced by the copolymerisation ratio between the two aromatic bisphenols.
. Togashi , S. Hasebe Journal of Thermal Science and Technology 2011 , 6 , 69 – 79 . “ Green benzylation of sodium salicylate by phase-transfer catalysis with third-liquid phase in a continuous two-phase-flow reactor ” H
. Kaizuka , K.-Y. Lee , H. Miyamura , S. Kobayashi Journal of Flow Chemistry 2012 , 2 , 1 – 4 . “ Phase-transfer catalysis under continuous flow conditions: An alternative approach to the biphasic liquid/liquid O-alkylation of
Thermal analysis characterization of isosorbide-containing thermosets
Isosorbide epoxy as BPA replacement for thermosets industry
Synthesis of New diols derived from dianhydrohexitols ethers under microwave-assisted phase transfer catalysis . Tetrahedron 56 32 5877 – 5883 10.1016/S0040-4020(00)00539-1 . 23. Chatti , S
. Tundo , P , Selva , M 1995 Simplify gas–liquid phase transfer catalysis . ChemTech 25 : 31 – 35 . 11. Fu , ZH , Ono , Y 1994 Selective α-monomethylation of phenylacetonitrile with