CO-CATALYSIS IN FRIEDEL–CRAFTS REACTIONS: VI. POLYMERIZATION OF 2-BUTENE BY BORON FLUORIDE – METHANOL

1963 ◽  
Vol 41 (4) ◽  
pp. 932-936 ◽  
Author(s):  
H. R. Allcock ◽  
A. M. Eastham
Keyword(s):  
Molecular Weight ◽  
Catalyst Concentration ◽  
Ethylene Dichloride ◽  
Low Molecular Weight ◽  
Boron Fluoride ◽  
First Order ◽  
Order Dependence ◽  
Rate Of Polymerization ◽  
Cis And Trans

2-Butene is polymerized by boron fluoride and methanol in ethylene dichloride solution at ordinary temperatures to give very low molecular weight polymers. The rate of polymerization shows exactly the same dependence on catalyst concentration as did the rate of isomerization of the cis- and trans-2-butenes, i.e. first order both in free boron fluoride and in the boron fluoride – methanol complex. The polymerization, however, shows a first-order dependence in olefin over a concentration range where the isomerization is, experimentally, virtually independent of the olefin concentration.

The effect of polymeric and model imidazolium halides on the rate of hydrolysis of 4-acetoxy-3-nitrobenzoic acid

1985 ◽  
Vol 50 (4) ◽  
pp. 845-853 ◽  
Author(s):  
Miloslav Šorm ◽  
Miloslav Procházka ◽  
Jaroslav Kálal
Keyword(s):  
Catalyst Concentration ◽  
Low Molecular Weight ◽  
Imidazolium Chloride ◽  
First Order ◽  
Nitrobenzoic Acid ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Hydrolysis Of ◽  
Ethanol In Water ◽  
Direct Attack

The course of hydrolysis of an ester, 4-acetoxy-3-nitrobenzoic acid catalyzed with poly(1-methyl-3-allylimidazolium bromide) (IIa), poly[l-methyl-3-(2-propinyl)imidazolium chloride] (IIb) and poly[l-methyl-3-(2-methacryloyloxyethyl)imidazolium bromide] (IIc) in a 28.5% aqueous ethanol was investigated as a function of pH and compared with low-molecular weight models, viz., l-methyl-3-alkylimidazolium bromides (the alkyl group being methyl, propyl, and hexyl, resp). Polymers IIb, IIc possessed a higher activity at pH above 9, while the models were more active at a lower pH with a maximum at pH 7.67. The catalytic activity at the higher pH is attributed to an attack by the OH- group, while at the lower pH it is assigned to a direct attack of water on the substrate. The rate of hydrolysis of 4-acetoxy-3-nitrobenzoic acid is proportional to the catalyst concentration [IIc] and proceeds as a first-order reaction. The hydrolysis depends on the composition of the solvent and was highest at 28.5% (vol.) of ethanol in water. The hydrolysis of a neutral ester, 4-nitrophenyl acetate, was not accelerated by IIc.

Characterization of Sol and Gel in Hevea Natural Rubber

1997 ◽  
Vol 70 (5) ◽  
pp. 707-713 ◽  
Author(s):  
Jitladda Tangpakdee ◽  
Yasukuki Tanaka
Keyword(s):  
Molecular Weight ◽  
Weight Fraction ◽  
Toluene Solution ◽  
Low Molecular Weight ◽  
Branch Points ◽  
Gel Content ◽  
High Ammonia ◽  
Linear Molecules ◽  
Cis And Trans

Abstract The gel content of rubber from high-ammonia latex (HA-latex) decreased significantly after deproteinization with proteolytic enzyme. The addition of 1–2% ethanol in toluene solution reduced the gel content of rubbers from HA-latex, deproteinized HA-latex (HA-DP) and pale crepe. Transesterification of the rubber in toluene solution with sodium methoxide dissolved the gel fraction. The gel fractions solubilized after transesterification showed molecular weight distribution rich in low molecular-weight fraction. The Huggins k′ constant of the fractionated rubbers from solubilized-gels was in the range of 0.42–0.45, lower than that of the fractionated HA-DP of 0.5–0.8. This indicates that all the branch-points were decomposed by transesterification to form linear molecules. The Mn values of rubber chains assembling the gel was 5.5−8.3×105 by 13C-NMR measurements of the ratio between cis- and trans-isoprene units, which were comparable to the molecular weight between crosslinks, Mc, of 7−11×105 by swelling measurements. These findings suggest that the branching and crosslinks are composed of two types of branch-points, i. e. one by association or aggregation of proteins or oligopeptides at the initiating end and the other by ester linkages including phosphoric ester at the terminal end.

CATIONIC POLYMERIZATION OF ETHYLENE OXIDE: IV. THE PROPAGATION REACTIONS

1960 ◽  
Vol 38 (10) ◽  
pp. 1967-1975 ◽  
Author(s):  
G. T. Merrall ◽  
G. A. Latrémouille ◽  
A. M. Eastham
Keyword(s):  
Molecular Weight ◽  
Ethylene Oxide ◽  
Cationic Polymerization ◽  
Chain Growth ◽  
Low Molecular Weight ◽  
Boron Fluoride

Studies of the boron-fluoride-catalyzed reaction of ethylene oxide with simple alcohols and low molecular weight polyglycols indicate three ways in which chain growth could occur, but only one of these is considered to be important after the initial stages of polymerization. The rate of disappearance of monomer reaches a maximum at a molecular weight of about 400. A mechanism is proposed to account for both polymerization and depolymerization and it is shown how equilibrium between these two reactions could result.

A Human Pharmacological Study Comparing Conventional Heparin and a Low Molecular Weight Heparin Fragment

1985 ◽  
Vol 53 (02) ◽  
pp. 208-211 ◽  
Author(s):  
G Bratt ◽  
E Törnebohm ◽  
D Lockner ◽  
G Bergströ
Keyword(s):  
Molecular Weight ◽  
Half Life ◽  
Low Molecular Weight Heparin ◽  
Pharmacological Study ◽  
Low Molecular Weight ◽  
Dose Dependency ◽  
First Order ◽  
First Order Kinetics ◽  
Heparin Activity ◽  
Different Doses

SummaryThe pharmacokinetics of a heparin fragment of low molecular weight (LMWH) of 4000-5000 D and unfractioned standard heparin (UFH) have been studied after i. v. injections of different doses and infusions in 8 humans.The heparin activity was significantly higher and the effect on APTT lower after LMWH fragment as compared to UFH in the same doses.The half-life of heparin activity was about 1 hr for UFH and about 2 hr for LMWH. LMWH was found to be eliminated according to first order kinetics and there were no signs of dose dependency.

Radioisomerization and Photoisomerization of Liquid 2 -Butenes in the Presence of Sulfur Compounds

1974 ◽  
Vol 52 (12) ◽  
pp. 2337-2340 ◽  
Author(s):  
Guy J. Collin ◽  
Patrick M. Perrin ◽  
François X. Garneau
Keyword(s):  
Molecular Weight ◽  
Hydrogen Sulfide ◽  
Liquid Phase ◽  
Molecular Oxygen ◽  
Carbon Disulfide ◽  
Sulfur Hexafluoride ◽  
The Other ◽  
Isomerization Reaction ◽  
Low Molecular Weight ◽  
Cis And Trans

The liquid phase radiolysis and photolysis of cis- and trans-2-butenes were studied in the presence of various additives. A very efficient isomerization of 2-butenes was achieved by the addition of thiols of low molecular weight (hydrogen sulfide, methyl and isopropyl mercaptans). In the absence of molecular oxygen, we have observed G values (trans-2-butene) of the order of 90 000. On the other hand, little or no isomerization occurred in the presence of carbon disulfide, sulfur hexafluoride, and tert-dodecylmercaptan. Although the majority of the additives have no effect on the 2-butene:hydrogen sulfide system, conjugated diolefins block the isomerization reaction. These diolefins disappear from the reaction mixture.

scholarly journals Comparing kinetic profiles between bifunctional and binary type of Zn(salen)-based catalysts for organic carbonate formation

2014 ◽  
Vol 10 ◽  
pp. 1817-1825 ◽  
Author(s):  
Carmen Martín ◽  
Arjan W Kleij
Keyword(s):  
Catalyst Concentration ◽  
Catalyst System ◽  
Bifunctional Catalyst ◽  
Cyclic Carbonates ◽  
First Order ◽  
Order Dependence ◽  
Carbonate Formation ◽  
Salen Complexes ◽  
Organic Carbonate ◽  
Binary Catalyst

Zn(salen) complexes have been employed as active catalysts for the formation of cyclic carbonates from epoxides and CO2. A series of kinetic experiments was carried out to obtain information about the mechanism for this process catalyzed by these complexes and in particular about the order-dependence in catalyst. A comparative analysis was done between the binary catalyst system Zn(salphen)/NBu4I and a bifunctional system Zn(salpyr)·MeI with a built-in nucleophile. The latter system demonstrates an apparent second-order dependence on the bifunctional catalyst concentration and thus follows a different, bimetallic mechanism as opposed to the binary catalyst that is connected with a first-order dependence on the catalyst concentration and a monometallic mechanism.

Water stress effects on the content of low molecular weight carbohydrates and phenolic acids in Ctenanthe setosa (Rosc.) Eichler

2000 ◽  
Vol 80 (2) ◽  
pp. 373-378 ◽  
Author(s):  
F. A. Ayaz ◽  
A. Kadioglu ◽  
R. Turgut
Keyword(s):  
Molecular Weight ◽  
Water Stress ◽  
Phenolic Acids ◽  
Phenolic Acid ◽  
Dry Weight ◽  
Low Molecular Weight ◽  
Leaf Rolling ◽  
Crystal Forms ◽  
Ctenanthe Setosa ◽  
Cis And Trans

Morphological and biochemical changes in plant cells are known as important events for adaptation to stress. In this study, changes in carbohydrate and phenolic acid concentrations during leaf rolling under water stress were investigated. Leaves of vegetatively propagated Ctenanthe setosa (Rosc.) Eichler plants started to roll after a 28-d water deficit. After approximately 33–35 d, the leaves were tightly rolled. Water stress significantly increased the dry weight of rolled leaves. Low molecular dry weight carbohydrate components identified in unrolled and rolled leaves were fructose, glucose, inositol and sucrose. Leaves of stressed plants tended to accumulate more carbohydrates of low molecular weight. The same sugars (except inositol) were also identified in liquid and crystal forms of exudates, which appeared on the abaxial surface of the leaves during leaf rolling. The phenolic acids identified in unrolled and rolled leaves were from the benzoic group (benzoic, salicylic, 4-hydroxybenzoic, vanillic, 3,4-dihydroxybenzoic, syringic acids), and the cinnamic group (ferulic and caffeic acids both in free and methyl ester form and cis- and trans-p-coumaric acids). All phenolic acid concentrations (except for salicylic acid) in the phenolic group increased in rolled leaves in comparison with unrolled leaves. In the cinnamic group, the amounts of cis- and trans-p-coumaric and caffeic acids were greater in rolled leaves than in unrolled leaves. Key words: Ctenanthe setosa, exudate, crystal, leaf rolling, sugar, phenolic acid

Polymerization of Butadiene with Alkylaluminum and Cobalt Chloride

1962 ◽  
Vol 35 (4) ◽  
pp. 1066-1082 ◽  
Author(s):  
Morris Gippin
Keyword(s):  
Molecular Weight ◽  
Cobalt Chloride ◽  
Polymer Molecular Weight ◽  
Cobaltous Chloride ◽  
First Order ◽  
Pyridine Complex ◽  
Fixed Concentration ◽  
Rate Of Polymerization ◽  
Butadiene Polymerization ◽  
Derivatives Of

Abstract The diethylaluminum chloride combination with cobaltous chloride or cobaltous chloride pyridinates requires water in a certain mole ratio to the diethylaluminum chloride to activate them as catalysts for butadiene polymerization at 5° C to 98% cis-1,4 structure. The cobalt-pyridine complex is the preferred component because of its ability to function in trace amounts. Several organic derivatives of water failed as substitutes. However, aluminum trichloride is effective as a substitute for water on an equimolar basis. The cis-1,4 content in the polymer decreases at higher polymerization temperatures. The higher pyridinates of cobaltous chloride tend to reduce the polymer molecular weight within narrow limits. The preferred solvent is benzene, in which the concentration of the monomer is a factor in both microstructure and polymer molecular weight. Certain mixtures of benzene and hexane provide another means of controlling molecular weight. The rate of polymerization is linear with respect to time in the initial stages, and is a first-order reaction with respect to monomer at a fixed concentration of catalyst.

Protection of Platelet Surface Bound Factors IX a and VIII Against Specific Inhibitors

1982 ◽  
Vol 47 (01) ◽  
pp. 032-035 ◽  
Author(s):  
Katalin Váradi ◽  
Susan Elödi
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Factor Ix ◽  
Low Molecular Weight ◽  
Platelet Surface ◽  
First Order ◽  
Enhanced Resistance ◽  
Phenylmethyl Sulfonyl Fluoride ◽  
Sulfonyl Fluoride ◽  
Specific Inhibitors

SummaryThe rate of inactivation of factors IX a and VIII as well as of the complex formed by them on the surface of platelets, induced by specific inhibitors has been studied. After the formation of complex both factors became more protected against high molecular weight inhibitors. As evidenced by the apparent first order inactivation rate constants, after complex formation the velocity of IX a – antithrombin III + heparin reaction fell to one-fourth, that of factor VIII – VIII : C antibody reaction decreased to 1/20. Enhanced resistance toward the high molecular weight inhibitors is presumably due to a steric change, since the low molecular weight phenylmethyl sulfonyl fluoride and diethyl pyrocarbonate inhibited free and complexed factor IX a to the same extent.

Retention of soluble99mTc-DTPA in the human lung: 24-h postdeposition

1997 ◽  
Vol 82 (4) ◽  
pp. 1378-1378 ◽  
Author(s):  
W. Michael Foster ◽  
Pamela T. Stetkiewicz ◽  
Arthur N. Freed
Keyword(s):  
Molecular Weight ◽  
Healthy Subjects ◽  
Human Lung ◽  
Lung Parenchyma ◽  
Respiratory Epithelium ◽  
Low Molecular Weight ◽  
Order Process ◽  
Epithelial Integrity ◽  
First Order ◽  
Lung Retention

Foster, W. Michael, Pamela T. Stetkiewicz, and Arthur N. Freed. Retention of soluble99mTc-DTPA in the human lung: 24-h postdeposition. J. Appl. Physiol.82(4): 1378–1382, 1997.—Clearance of low-molecular-weight solutes, e.g., radiolabeled chelate diethylenetriaminepentaacetate (DTPA), across epithelial surfaces of distal airways and the lung parenchyma is a broadly used technique to assess epithelial integrity. It has been generally assumed that clearance of solute follows a simple first-order process and that DTPA clearance through the respiratory epithelium and into blood and lymphatic channels is complete within a few hours. Using γ-camera imaging and a radiolabeled aerosol of99mTc-labeled DTPA, we observed in eight healthy subjects lung retention of radioisotope ∼24 h postdeposition of the 99mTc-DTPA. Residual lung retention at the 24-h end point averaged 6.0 ± 1.8 (SD)% of the amount of radioisotope initially deposited in the lung. This suggests that for normal healthy subjects a small amount of the99mTc radioisotope, either in a dissociated or chelated form, is nonpermeable or slowly cleared from respiratory tisssues.

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