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Slow Addition (slow + addition)
Selected AbstractsSharpless Asymmetric Dihydroxylation of Olefins in WaterSurfactant Media with Recycling of the Catalytic System by Membrane NanofiltrationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2008Abstract This paper presents a new and more sustainable alternative approach for the Sharpless catalytic asymmetric dihydroxylation (AD) of olefins using a water/surfactant system as reaction media. The AD reaction was performed using several cationic and anionic surfactants allowing yields and enantiomeric excesses higher or comparable with the conventional systems (using organic mixtures). The use of this water/surfactant medium offers the additional advantage of performing the reactions without the need of a slow addition of olefins. Asymmetric dihydroxylation of 1-hexene in a 1.5,mM sodium cholate aqueous solution, using N -methylmorpholine N -oxide (NMO) as co-oxidant was selected as model system to evaluate the feasibility of recycling the Sharpless catalytic system by nanofiltration. The reaction media was processed by nanofiltration, the product was isolated in the permeate, whereas the catalytic system and surfactant were retained by the membrane and recycled through six successive reactions, improving the catalyst turn-over number. The experimental results were compared with the ones calculated on the basis of mass balances, membrane rejections to product and reaction yields. [source] Ammoximation of methyl ethyl ketone with H2O2 and ammonia over TS-1JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2006Li Wang Abstract The ammoximation of methyl ethyl ketone and hydrogen peroxide to form methyl ethyl ketoxime was studied over zeolites (TS-1) in the temperature range 308,373 K. The reaction was carried out in a batch autoclave at autogenous pressure. The conversion of methyl ethyl ketone and the selectivity to methyl ethyl ketoxime can reach 99% and approximately 100%, respectively, and the by-products were the small amounts of corresponding methyl ethyl ketazine and trace amounts of unidentified compounds. Important factors were the reaction temperature, solvents and slow addition of hydrogen peroxide. The molar ratio of NH3 to ketone had no significant effect on the conversion of methyl ethyl ketone, but increase in the ratio of NH3 to ketone had a beneficial effect on selectivity. Copyright © 2006 Society of Chemical Industry [source] Promoted random orientation of the phenyl substituent of phenylhydroquinone,terephthalic acid polyesters prepared with a diphenyl chlorophosphate/pyridine condensing agentJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2001Fukuji Higashi Abstract The reaction of sterically hindered hydroxyl groups at the 2-position of methylhydroquinone and phenylhydroquinone (PhHQ) to form esters was largely promoted by their slow addition to benzoic acid activated by diphenyl chlorophosphate in pyridine. A modification of this reaction was applied to the preparation of thermotropic terephthalic acid/PhHQ and 2,5-dichloroterephthalic acid/PhHQ polymers with randomly oriented phenyl substituents, and the properties of the polymers were studied in terms of their transition temperatures, which were determined by differential scanning calorimetry and microscopic observation. The melting points were lowered by about 30,50 °C by the dropwise addition of PhHQ over 10,30 min. The molecular structures of the 2,5-dichloroterephthalic acid/PhHQ polymers were studied by 13C NMR. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1726,1732, 2001 [source] Synthesis and characterization of hyperbranched polytriazole via an ,A2 + B3' approach based on click chemistryPOLYMER INTERNATIONAL, Issue 8 2008Jianda Xie Abstract BACKGROUND: The ,A2 + B3' type of polymerization has been demonstrated to be an alternative route towards hyperbranched polymers. Some highly crosslinked hyperbranched polymers have been prepared via copper(I)-catalyzed click reactions of multivalent azides and alkynes. To obtain hyperbranched polymers without gelation and develop the A2 + B3 type of polymerization based on click reactions, the specific reaction conditions need to be investigated. RESULTS: In this work, a hyperbranched polytriazole (hb -PTA) was synthesized through the A2 + B3 approach using a click reaction. 4- N,N,-bis(2-azidoethyl)amino-4,-nitroazobenzene and 1,3,5-tris(alynyloxy)benzene were synthesized for use as the A2 and B3 monomers, respectively. This was a ,one-pot' polymerization carried out using a slow-addition method. The obtained hb -PTA was soluble in common organic solvents. The molecular structure was characterized using 1H NMR, Fourier transform infrared and gel permeation chromatography analyses. The degree of branching of hb -PTA was determined to be around 0.50. CONCLUSION: The hb -PTA was successfully synthesized via the A2 + B3 approach based on a click reaction. The polymerization conducted in dilute solution adopting slow addition of A2 to B3 resulted in hb -PTA in the absence of gelation. The obtained hb -PTA exhibited high thermal stability. Copyright © 2008 Society of Chemical Industry [source] | |||||||||||||