Search Results
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.
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
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
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.
Conventional batch dibromocyclopropanations by reaction of bromoform and alkenes under phase-transfer conditions require strong base (50% NaOH (aq)), vigorous stirring, and often long reaction times. Using flow chemistry in a microreactor, the reactions were found to be smooth, rapid, and high-yielding under ambient conditions when 40% (w/w) NaOH was used as the base. The reaction has been tested with a representative selection of alkenes, displaying a variety of structural features.
Liquid crystalline polymers
III. Characterization by thermo-optometry of some copolyethers containing an oxetane ring in the main chain
The suitabilities of thermo-optometry and differential scanning calorimetry for the characterization of certain copolyethers were compared. Under certain conditions, such polymers do not exhibit the endotherm signal corresponding to the solid/liquid crystalline transition in the DSC curves. Thermo-optometry provides evidence of these phase transitions into the liquid crystalline state, and is a very useful additional method.
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
