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131.
Eugenia M. Brazwell Dianela Y. Filos Cary J. Morrow 《Journal of polymer science. Part A, Polymer chemistry》1995,33(1):89-95
Enzyme-catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures and has been studied for several years. A significant limitation on the polyesters prepared to date has been the low molecular weights achieved. The present studies have established that, in the polycondensation of bis(2,2,2-trifluoroethyl) glutarate with 1,4-butanediol using porcine pancreatic lipase as the catalyst, this limitation arises from at least two sources: hydrolysis of activated ester end groups by water introduced along with the enzyme and the polymerization's reaching equilibrium despite using the poorly nucleophilic 2,2,2-trifluoroethanol as the leaving group. Evidence is also developed that the presence of trifluoroethanol accelerates the release of the enzyme-bound water which hydrolyzes the activated ester end groups. The hydrolysis could be avoided by choosing a relatively high-boiling solvent, such as bis(2-ethoxyethyl) ether, then removing the trifluoroethanol by placing the reaction mixture under vacuum periodically or by drying the enzyme rigorously. The vacuum method also removed the limitation on molecular weight resulting from the reaction's reaching equilibrium. A further improvement in the molecular weight to nearly 40,000 daltons, well within the range that is technically interesting, was achieved by using 1,2-dimethoxybenzene or 1,3-dimethoxybenzene as the polymerization solvent. © 1995 John Wiley & Sons, Inc. 相似文献
132.
On the Crystal Structures of CH3PF2H+AsF6? and CH3PF2H+SbF6? and a simple Method for Preparation of CH3PF2 A simple method for preparation of CH3PF2 from CH3PCl2 is reported. The phosphonium salts CH3PF2H+MF6? are obtained by the reaction of CH3PCl2 with superacidic systems HF/MF5 (M = As, Sb). CH3PF2H+SbF6? crystallizes in the space group P1 with a = 548.4(4) pm, b = 695.5(8) pm, c = 960.2(9) pm, α = 94.68(5)°, β = 97.19(6)°, γ = 94.41(6)° and Z = 2. CH3PF2H+SbF6? crystallizes in P1 with a = 554.3(3), b = 724.2(4), c = 970.4(5), α = 94.73(4)°, β = 96.14(5)°, γ = 95.30(4)°. 相似文献
133.
Synthesis and Structure of the First Ternary Lead(II) Copper(I) Oxide: PbCu2O2 PbCu2O2 can be prepared by solid state reaction or by precipitation from a basic aqueous solution. Single crystals of the new compound were prepared by recrystallisation from a molten mixture (PbO? Cu2O) and investigated by X-ray diffractometer technique. PbCu2O2 crystallizes isotypically with the homologue silver compound PbAg2O2 (monoclinic with a = 8.223 Å, b = 8.289 Å, c = 6.015 Å, β = 132.62°, Z = 4, space group C? C 1 2/c 1). The crystallographic data from the X-ray investigation are reported. The structure is built by endless [PbO4/4]- and [CuO2/4]-chains. Pb2+ has a one-sided asymmetric coordination with four next oxygen neighbours and Cu+ forms a stretched dumbbell with two oxygen atoms. 相似文献
134.
Diphenylphosphine oxidatively adds to the ReRe bonds of Re2
X
4(-dppm)2 (X=Cl or Br; dppm=Ph2PCH2PPh2) and Re2Cl4(-dpam)2 (dpam=Ph2AsCH2AsPh2) to afford the dirhenium(III) complexes Re2(-X)(-PPh2)HX
3(-LL)2. The dppm complexes have also been prepared from the reactions of Re2(-O2CCH3)X
4(-dppm)2 with Ph2PH, and a similar strategy has been used to prepare Re2(-Cl)(-PPh2)HCl3(-dmpm)2 (dmpm=Me2PCH2PMe2) from Re2(-O2CCH3)Cl4(dmpm)2. Phenylphosphine likewise reacts with Re2
X
4(-dppm)2 to give Re2(-X)(-PHPh)HX
3(-dppm)2. An X-ray crystal structure determination on Re2(-Cl)(-PPh2)HCl3(-dppm)2 confirms its edge-shared bioctahedral structure. This complex crystallizes in the space group
(No. 148) witha=21.699(3) Å, =84.50(4)°,V=10084(5) Å3, andZ=6. The structure was refined toR=0.049 (R
w
0.069) for 5770 data withI>3.0(I). The Re-Re distance is 2.5918(7) Å. Oxidation of the bromide complex Re2(-Br)(-PPh2)HBr3(-dppm)2 with NOPF6 produces the unusual dirhenium(III, II) cation [Re2(-H)(-Br)[P(O)Ph2]Br2(NO)(-dppm)2]+ which has been structurally characterized as its perrhenate salt, [Re2(-H)(-Br)[P(O)Ph2]Br2(NO)(-dppm)2]ReO4 · 2CH2Cl2. This complex crystallizes in the space group
(No. 2) witha=14.187(7) Å,b=16.419(5) Å,c=16.729(5) Å, =98.76(2)°, =110.11(3)°, =104.66(3)°,V=3414(6) Å3,Z=2. The structure was refined toR=0.040 (R
w
=0.051) for 5736 data withI>3.0(I). The presence of a phosphorus-bound [P(O)Ph2]– ligand, a linear nitrosyl and a bridging hydrido ligand has been confirmed. The Re-Re distance is 2.6273(8) Å. 相似文献
135.
Vera P. Shmachkova Nina S. Kotsarenko Vladislav V. Kanazhevskiy Galina N. Kryukova Dimitri I. Kochubey Jacques Vedrine 《Reaction Kinetics and Catalysis Letters》2007,91(1):177-185
Methods of the preparation of catalysts for alkane skeletal isomerization based on uniform nanoparticles of sulfated zirconia
anchored to different supports were investigated. These catalysts were characterized by using the ICP, HRTEM and BET techniques.
The activities of the catalysts in the reaction of n-butane isomerization were measured and compared with those of bulk catalysts. 相似文献
136.
将Fe2O3纳米粉体经一定浓度的H2SO4浸泡活化后制成纳米固体超强酸SO42-/Fe2O3,将其用于催化合成乙酸乙酯以考察其活性。利用均匀设计分析了超强酸制备过程及酯化反应过程中各因素的影响,研究结果表明较好的制备条件是:H2SO4浓度:2.5mol·L-1;浸泡时间:1h;活化温度:167℃;活化时间:1h,此时获得的固体超强酸SO42-/Fe2O3的粒径小于50nm。当催化剂用量为冰乙酸质量的5%,n(乙醇)∶n(冰乙酸)为3∶1,反应3.5h后乙酸的转化率高于80%。该催化剂经H2SO4溶液浸泡、活化再生后可重新使用,推断出其酸强度H0<-14.5。 相似文献
137.
The state of art of the various preparative planar liquid chromatographic (PLC) methods is summarized, especially for off-line and on-line sample application. The sample purification possibilities for PLC techniques are discussed. Purification and isolation strategies using forced-flow planar chromatographic techniques, such as overpressured layer chromatography and rotation planar chromatography, are suggested in the form of flow charts. 相似文献
138.
139.
单分散二氧化钛超微粒子的制备 总被引:10,自引:0,他引:10
以四丁氧基钛为原料,采用溶胶-凝胶法制备了超微二氧化钛粉末.改变热处理气氛、升温速率、水与四丁氧基钛的摩尔比以及溶剂,分别得到7nm球形单相锐钛矿以及四方形(40nm×10nm)、球形(44nm)的主相金红石超微粒子. 相似文献
140.
可再生甲壳素吸附铬(Ⅵ)的特性研究 总被引:9,自引:0,他引:9
可再生甲壳素吸附铬(Ⅵ)的特性研究陈炳稔*汤又文李国明万春华(华南师范大学化学系广州510631)关键词可再生甲壳素,制备,铬(Ⅵ),吸附1997-08-19收稿,1997-12-23修回广东省科委及高教厅资助课题利用甲壳素作为铬(Ⅵ)的捕集剂已有报... 相似文献