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.

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 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.

Highly functionalized alkenes produced from base-free organocatalytic Wittig reactions: (E)-3-benzylidenepyrrolidine-2,5-dione, (E)-3-benzylidene-1-methylpyrrolidine-2,5-dione and (E)-3-benzylidene-1-tert-butylpyrrolidine-2,5-dione

2016 ◽  
Vol 72 (6) ◽  
pp. 504-508 ◽  
Author(s):  
Marie-Luis Schirmer ◽  
Anke Spannenberg ◽  
Thomas Werner
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Carbonyl Compounds ◽  
Wittig Reaction ◽  
Phosphonium Salts ◽  
Asymmetric Unit ◽  
Free Base ◽  
Fundamental Transformation ◽  
Wittig Reactions ◽  
Centrosymmetric Dimers

The Wittig reaction is a fundamental transformation for the preparation of alkenes from carbonyl compounds and phosphonium ylides. The ylides are prepared prior to the olefination step from the respective phosphonium salts by deprotonation utilizing strong bases. A first free-base catalytic Wittig reaction for the preparation of highly functionalized alkenes was based on tributylphosphane as the catalyst. Subsequently we developed a system employing a phospholene oxide as a pre-catalyst and trimethoxysilane as reducing agent which operates under milder conditions. The title compounds, (E)-3-benzylidenepyrrolidine-2,5-dione, C11H9NO2, (I), the methylpyrrolidine derivative, C12H11NO2, (II), and thetert-butylpyrrolidine derivative, C15H17NO2, (III), have been synthesized by base-free catalytic Wittig reactions. In the crystal of (I), molecules are linked into centrosymmetric dimersviapairs of N—H...O hydrogen bonds. Furthermore, in the crystal structure of (III), there are two molecules in the asymmetric unit, whereas in (I) and (II), only one molecule is present.

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.

Polymerization of Nitrophenyl and 3-Diethylaminophenyl Prop-2-yn-1-yl Ethers with PdCl2. Polymers and Copolymers Characterization

1998 ◽  
Vol 63 (11) ◽  
pp. 1803-1814 ◽  
Author(s):  
Hynek Balcar ◽  
Petr Holler ◽  
Jan Sedláček ◽  
Vratislav Blechta
Keyword(s):  
Molecular Weight ◽  
Dimethyl Sulfoxide ◽  
Size Exclusion Chromatography ◽  
Main Chain ◽  
Size Exclusion ◽  
Low Molecular Weight ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Exclusion Chromatography

2-, 3- and 4-Nitrophenyl prop-2-yn-1-yl ethers were polymerized with PdCl2 in N,N-dimethylformamide (DMF) giving brown polymers soluble in DMF, dimethyl sulfoxide and N-methylpyrrolidone. Broad (mostly bimodal) molecular weight distributions were observed by size-exclusion chromatography (SEC) with maxima at molecular weight of about 4 . 103 and 1 . 105. With the same catalyst, 3-diethylaminophenyl prop-2-yn-1-yl ether gave predominantly low molecular weight homopolymer (Mn = 4 200) soluble in DMF, N-methylpyrrolidone, CHCl3 and tetrahydrofuran-soluble copolymers with 4-nitrophenyl prop-2-yn-1-yl ether (Mn about 3 000). IR, NMR and UV-VIS spectra of prepared polymers and copolymers proved the structure to consist of the polyene-type main chain with phenoxymethyl pendant groups bearing nitro or diethylamino substituents.

Thermal Dehydrochlorination of Poly(vinyl chloride) in Syndiotactic Systems

1992 ◽  
Vol 57 (1) ◽  
pp. 93-106 ◽  
Author(s):  
Jaroslav Burda ◽  
Rudolf Lukáš
Keyword(s):  
Molecular Weight ◽  
Reaction Mechanism ◽  
Hydrogen Chloride ◽  
Vinyl Chloride ◽  
Quantum Chemical ◽  
Low Molecular Weight ◽  
Ionic Mechanism ◽  
Reaction Conditions ◽  
Poly Vinyl Chloride ◽  
Ionic Intermediates

The thermal dehydrochlorination of syndiotactic poly(vinyl chloride) sequences has been studied theoretically on low-molecular weight models ranging from vinyl chloride dimer to pentamer using the semiempirical quantum chemical MNDO method. Parameters obtained with saturated systems and their change caused by the proceeding elimination of hydrogen chloride accompanied by the formation of the corresponding unsaturated structures are discussed with respect to the repeated chloroallyl or α-chloropolyene activation of the dehydrochlorination process. The study of the assumed radical and ionic intermediates is used in discussing the reaction mechanism of dehydrochlorination, and the radical or ionic mechanism is supposed to be operative depending on the reaction conditions.

scholarly journals Low‐molecular‐weight carbohydrate Pentaisomaltose may replace dimethyl sulfoxide as a safer cryoprotectant for cryopreservation of peripheral blood stem cells

Transfusion ◽  
2016 ◽  
Vol 56 (5) ◽  
pp. 1088-1095 ◽  
Author(s):  
Jesper Dyrendom Svalgaard ◽  
Eva Kannik Haastrup ◽  
Kristian Reckzeh ◽  
Bjørn Holst ◽  
Peter Viktor Glovinski ◽  
...  
Keyword(s):  
Stem Cells ◽  
Molecular Weight ◽  
Dimethyl Sulfoxide ◽  
Peripheral Blood ◽  
Low Molecular Weight ◽  
Peripheral Blood Stem Cells ◽  
Blood Stem Cells
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