scholarly journals Aerobic Epoxidation of Low-Molecular-Weight and Polymeric Olefins by a Supramolecular Manganese Porphyrin Catalyst

Catalysts ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 195 ◽  
Author(s):  
Ivan Bernar ◽  
Floris Rutjes ◽  
Johannes Elemans ◽  
Roeland Nolte
Keyword(s):  
Molecular Weight ◽  
Ambient Temperature ◽  
High Activity ◽  
Molecular Oxygen ◽  
Low Molecular Weight ◽  
Mechanistic Studies ◽  
Manganese Porphyrin ◽  
Reaction Conditions ◽  
Porphyrin Complex ◽  
Epoxidation Reaction

We report on the highly efficient epoxidation of low-molecular-weight and polymeric olefins catalyzed by a supramolecular manganese porphyrin complex using molecular oxygen as an oxidant and an aldehyde as a co-reductant. At ambient temperature and under optimized reaction conditions, the catalyst showed high activity and stereoselectivity. The efficiency of the supramolecular manganese porphyrin was higher than that of a reference porphyrin catalyst, possibly because it was more stable under the applied reaction conditions. Mechanistic studies suggest that a manganese oxo porphyrin complex may be an intermediate in the epoxidation reaction.

SYNTHESIS OF ISOTOPICALLY LABELLED OLEFINS VIA THE WITTIG REACTION

1965 ◽  
Vol 43 (5) ◽  
pp. 1614-1624 ◽  
Author(s):  
J. G. Atkinson ◽  
M. H. Fisher ◽  
D. Horley ◽  
A. T. Morse ◽  
R. S. Stuart ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Dimethyl Sulfoxide ◽  
Wittig Reaction ◽  
Low Molecular Weight ◽  
Phosphonium Salts ◽  
Reaction Conditions ◽  
Selective Labelling ◽  
Wittig Reactions

A new application of the Wittig reaction to the preparation of olefins of low molecular weight which allows selective labelling in the vinyl or allyl positions with isotopes of hydrogen and carbon has been developed. Using the modification of the Wittig reaction introduced by E. J. Corey, in which a solution of the methylsulfinyl carbanion in dimethyl sulfoxide serves as the base, a series of olefins from C2 to C8 were synthesized. The synthesis was applied to the preparation of the following labelled compounds: 5-methylene-14C-bicyclo[2.2.1]hept-2-ene; propene-1-14C; 1-butene-1-14C; propene-1-d1; 2-methylpropene-1,1-d2; 2-methyl-d3-propene-3,3,3-d3; 2-methyl-2-butene-4,4,4-d3; 2-methyl-d3-2-butene-1,1,1-d3; methylene-d2-cyclohexane. For the synthesis of carbon-labelled olefins the reaction has few limitations since the intermediates and products are isotopically stable under the reaction conditions. Deuterium-labelled olefins can be obtained from deuterated formaldehyde or β-deuterated phosphonium salts, but α-deuteroketones and aldehydes and α-deuterophosphonium salts lose the isotope to the solvent.In all the Wittig reactions, benzene was formed as a by-product in 10–15% yield. The mechanism of benzene formation is probably analogous to that proposed by Seyferth involving the decomposition of a pentacovalent phosphorous intermediate.

Immobilization of enzymes on alumina by means of pyridoxal 5′-phosphate

1988 ◽  
Vol 8 (3) ◽  
pp. 263-269 ◽  
Author(s):  
M. Pugnière ◽  
C. San Juan ◽  
M-A. Coletti-Previero ◽  
A. Previero
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
High Activity ◽  
Immobilized Enzymes ◽  
Second Step ◽  
Low Molecular Weight ◽  
Step Procedure ◽  
Immobilization Of Enzymes

A number of proteases have been immobilized on alumina in a two-step procedure: the first step converted them into semisynthetic phosphoproteins which, in the second step, spontaneously bonded to alumina through their phosphate function. The immobilized enzymes thus obtained showed the physical properties typical of the inorganic carrier and a high activity on low molecular weight substrates.

The Research of Silane Oligomer with Lower Valatilization Rate for Protecting Concrete

2013 ◽  
Vol 357-360 ◽  
pp. 1318-1322 ◽  
Author(s):  
Hong Yao Sun ◽  
Zheng Yang ◽  
Gao Xia Sun ◽  
Xue Feng Xu
Keyword(s):  
Molecular Weight ◽  
Gel Permeation Chromatography ◽  
Chloride Ions ◽  
Polymerization Reaction ◽  
Low Molecular Weight ◽  
Construction Process ◽  
Reaction Conditions ◽  
Hydrophobic Agent ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

As one of the measures to improve the durability of concrete, silane penetrating hydrophobic agents can preserve the properties of respiratory function of concrete and can prevent the penetration from harmful medium such as chloride ions. Because of low molecular weight of the silane penetrating hydrophobic agent such as isobutyl triethoxysilane, high volatilization rate of silane can result in waste of material in construction process. The silane oligomer was obtained by radical polymerization reaction with suitable monomers, initiators and reaction conditions. Furthermore, we verified the structure of the silane oligomer by FT-IR spectroscopy and got its molecular weight by GPC(Gel Permeation Chromatography). The silane oligomer with lower volatilization rate has excellent properties of hydrophobicity, higher penetration depth and resistance to chloride ions penetration.

Dehydrochlorination of Poly(vinyl chloride) in Isotactic Systems

1993 ◽  
Vol 58 (2) ◽  
pp. 343-353 ◽  
Author(s):  
Jaroslav Burda ◽  
Rudolf Lukáš
Keyword(s):  
Molecular Weight ◽  
Point Of View ◽  
Low Molecular Weight ◽  
Ionic Mechanism ◽  
Polyene Chain ◽  
Subsequent Growth ◽  
Reaction Conditions ◽  
Poly Vinyl Chloride ◽  
Semiempirical Mndo ◽  
Thermodynamic Factors

The dehydrochlorination of isotactic, low-molecular-weight models of PVC, dimers to pentamers, was studied using the semiempirical MNDO method. The results obtained lead to the conclusion that the thermal dehydrochlorination of PVC can occur through either a radical or an ionic mechanism, depending on the reaction conditions. The arising conjugated polyene structures do not grow by the generally accepted "zip" mechanism, but rather through the "alternating growth" mechanism. A comparison was also made to the reactivity of isotactic and syndiotactic sequences from the point of view of kinetic and thermodynamic factors. It follows from the computations that the splitting off of the first HCl molecule is easier in the isotactic sequence, but that subsequent growth of the polyene chain occurs more readily in syndiotactic systems.

scholarly journals Synthesis of a Chiral Meso-Like Ansa-Zirconocene Complex and its Use for the Catalytic Formation of Low Molecular Weight Polypropylene

1995 ◽  
Vol 50 (6) ◽  
pp. 982-989 ◽  
Author(s):  
Sven Thiele ◽  
Gerhard Erker ◽  
Cornelia Fritze ◽  
Christian Psiorz ◽  
Roland Fröhlich
Keyword(s):  
Crystal Structure ◽  
Molecular Weight ◽  
Double Bond ◽  
Ambient Temperature ◽  
Organic Synthesis ◽  
Crystal Structure Analysis ◽  
Low Molecular Weight ◽  
X Ray ◽  
Catalyst Systems ◽  
Double Bond Shift

Reaction of lithium(neomenthylcyclopentadienid) 3 with dimethyldichlorosilane gives dimethylbis[3-(neomenthyl)cyclopentadienyl]silane 4 regioselectively as a mixture of double bond shift isomers (57% isolated). Deprotonation with 2 equiv. of butyllithium followed by treatment with zirconiumtetrachloride furnished a mixture of the three {dimethylsilylenbis[η5-3-(neomenthyl)cyclopentadienyl][zirconium dichloride diastereomers from which the pure meso-like isomer 6e [p -R (1′S ,3 ′R ,4 ′R),p -S (1′S ,3 ′R ,4 ′R)] was isolated by fractional crystallization. Complex 6 c was characterized by an X-ray crystal structure analysis. Its D 1 - Zr - D 2 angle of 126.8° is very similar as observed in bis(η-cyclopentadienyl) zirconium dichloride (D 1 and D 2 denote the centroids of the cyclopentadienyl rings). The homogeneous 6c/methylalumoxane Ziegler-type catalyst produces polypropylene of low molecular weight (Mη ≈ 670 at ambient temperature). Related catalyst systems may find interesting applications in organic synthesis.

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.

Efficient oxidations and photooxidations with molecular oxygen using metal phthalocyanines as catalysts and photocatalysts

2004 ◽  
Vol 08 (08) ◽  
pp. 1020-1041 ◽  
Author(s):  
Dieter Wöhrle ◽  
Olga Suvorova ◽  
Robert Gerdes ◽  
Oliver Bartels ◽  
Lukasz Lapok ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Molecular Oxygen ◽  
Heterogeneous Catalysts ◽  
Ion Exchanger ◽  
Photochemical Synthesis ◽  
Low Molecular Weight ◽  
Oxidation Reactions ◽  
Metal Phthalocyanines ◽  
Catalytic Oxidations ◽  
Different Types

Metal phthalocyanines can be very efficient as catalysts and photocatalysts in oxidation reactions using molecular oxygen as oxidant. Different types of soluble low molecular weight or oligomeric and insoluble heterogeneous catalysts and photocatalysts were developed. The heterogeneous metal phthalocyanines exist either impregnated on SiO 2, Al 2 O 3, charcoal and TiO 2 or covalently and coordinatively bound on SiO 2 and organic polymers or ionically bound on an organic ion exchanger. The catalytic oxidations of toxic sulfide and thiol derivative are studied. In addition, toxic phenols were employed as substrates for the photooxidation. Heterogeneous catalysts can exhibit higher activities then low molecular weight phthalocyanines. These systems exhibit a good stability for re-use. Photooxidations are more efficient than oxidations. A Si(IV) phthalocyanine derivative on a polymer ion exchanger is most active and stable. Also some examples for photooxidations in the direction of photochemical synthesis are given.

End Groups of Oxidized Rubber

1958 ◽  
Vol 31 (1) ◽  
pp. 86-88
Author(s):  
E. M. Bevilacqua
Keyword(s):  
Molecular Weight ◽  
Oxygen Consumption ◽  
Peroxy Radical ◽  
Chain Scission ◽  
Low Molecular Weight ◽  
Reaction Conditions ◽  
Detailed Mechanism ◽  
End Groups

Abstract Chain scission during the oxidation of polymeric 1,5-dirnethyl-l,5-dienes occurs nearly quantitatively through the scission of an unusual peroxidic intermediate, followed ultimately by evolution of a group of fragments of low molecular weight at each scission. The composition of this group depends on the reaction conditions. The first known stable intermediates to be formed subsequent to scission are levulinaldehyde and formaldehyde: Bolland's kinetic and analytic studies combined with the requirements of the observed stoichiometry of scission form the basis on which it is possible to write a detailed mechanism for the transformation represented by Equation 1. Nothing is known in detail of the sequence of reactions resulting in Equation 2. It has been suggested that scission is associated with propagation rather than initiation—that is, with decomposition of a peroxy radical rather than of a hydroperoxide as is indicated in this scheme. This is still a moot point. It is now known, for example, that overall scission efficiency is strongly determined by temperature and that benzothiazolethione and o,o′-dibenzamidodiphenyldisulfide both accelerate oxygen consumption as well as scission, in contrast to earlier belief.

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