Halogenated poly(isobutylene-co-isoprene): influence of halogen leaving-group and polymer microstructure on chemical reactivity

2013 ◽  
Vol 91 (6) ◽  
pp. 420-427 ◽  
Author(s):  
Joanne R. McNeish ◽  
J. Scott Parent ◽  
Ralph A. Whitney
Keyword(s):  
Thermal Stability ◽  
Nucleophilic Substitution ◽  
Low Temperatures ◽  
Chemical Reactivity ◽  
Polymer Microstructure ◽  
Leaving Group ◽  
Sulfur Vulcanization ◽  
Chlorobutyl Rubber ◽  
Leaving Group Ability ◽  
Effect Of Microstructure

Brominated (BIIR) and chlorinated (CIIR) poly(isobutylene-co-isoprene) are commercially available materials commonly known as halobutyl rubbers. The effect of leaving-group ability on the reactivity of halogenated poly(isobutylene-co-isoprene) was studied to place iodobutyl rubber reactivity into context with these materials. The effect of microstructure on reactivity of existing commercial materials was studied through comparison to that of polymers containing rearranged halomethyl (r-CIIR, r-BIIR, and r-IIIR) microstructure (prepared from as-received BIIR). The effect of leaving group on both thermal stability and reactivity towards nucleophilic substitution with acetate, N-butylimidazole, and sulfur was examined. The material containing the iodomethyl microstructure (r-IIIR) readily underwent nucleophilic substitution at low temperatures; however, it was extremely sensitive towards dehydrohalogenation at temperatures above 65 °C. At temperatures between 100 and 135 °C, the material containing the bromomethyl microstructure (r-BIIR) demonstrated the greatest balance between reactivity toward nucleophilic substitution and elimination through dehydrohalogenation. Exceptional thermal stability at temperatures up to 190 °C was displayed by the material containing the chloromethyl microstructure (r-CIIR); however, its reactivity towards nucleophiles was variable and nucleophile dependent. Sulfur vulcanization studies showed a clear effect of microstructure on the ability to cure with sulfur. While commercial chlorobutyl rubber has no ability to cure with sulfur alone, when rearranged to its chloromethyl microstructure (r-CIIR), curing occurs readily. Both commercial (BIIR) and rearranged (r-BIIR) bromobutyl rubber readily vulcanize in the presence of sulfur; however, BIIR cures to a greater extent.

scholarly journals Leaving Group Ability in Nucleophilic Aromatic Amination by Sodium Hydride–Lithium Iodide Composite

Synthesis ◽  
2019 ◽  
Vol 52 (03) ◽  
pp. 393-398
Author(s):  
Jia Hao Pang ◽  
Derek Yiren Ong ◽  
Kohei Watanabe ◽  
Ryo Takita ◽  
Shunsuke Chiba
Keyword(s):  
Nucleophilic Substitution ◽  
Methoxy Group ◽  
Sodium Hydride ◽  
Lithium Iodide ◽  
Substitution Reactions ◽  
Computational Approaches ◽  
Nucleophilic Substitution Reactions ◽  
Leaving Group ◽  
Leaving Group Ability

The methoxy group is generally considered as a poor leaving group for nucleophilic substitution reactions. This work verified the superior ability of the methoxy group in nucleophilic amination of arenes mediated by the sodium hydride and lithium iodide through experimental and computational approaches.

scholarly journals Nucleophilic substitution at di- and triphosphates: leaving group ability of phosphate versus diphosphate

2019 ◽  
Vol 1 (2) ◽  
pp. 024001 ◽  
Author(s):  
Bas van Beek ◽  
Marc A van Bochove ◽  
Trevor A Hamlin ◽  
F Matthias Bickelhaupt
Keyword(s):  
Nucleophilic Substitution ◽  
Leaving Group ◽  
Leaving Group Ability

Effect of the hydrophilicity of the polymer matrix on immobilized α-chymotrypsin

1984 ◽  
Vol 49 (6) ◽  
pp. 1552-1556
Author(s):  
Minoru Kumakura ◽  
Isso Kaetsu
Keyword(s):  
Thermal Stability ◽  
Enzyme Activity ◽  
Pore Size ◽  
Polymer Matrix ◽  
Low Temperatures ◽  
Radiation Polymerization ◽  
Thermal Stability Of

α-Chymotrypsin was immobilized by radiation polymerization at low temperatures and the effect of the hydrophilicity of the polymer matrix on the enzyme activity and thermal stability was studied. The activity and thermal stability of immobilized chymotrypsin increased with the increasing hydrophilicity of the polymer matrix or monomer. The thermal stability was affected by the form and pore size of the polymer matrix; chymotrypsin immobilized on a soft-gel polymer matrix exhibited an enhanced thermal stability.

Enhancement of thermal stability and chemical reactivity of phenolic resin ameliorated by nanoSiO2

2017 ◽  
Vol 35 (1) ◽  
pp. 298-302 ◽  
Author(s):  
Yajun Guo ◽  
Lihong Hu ◽  
Puyou Jia ◽  
Baofang Zhang ◽  
Yonghong Zhou
Keyword(s):  
Thermal Stability ◽  
Phenolic Resin ◽  
Chemical Reactivity

Leaving group ability in base-promoted alkene-forming 1,2-eliminations

1975 ◽  
pp. 940 ◽  
Author(s):  
Donald R. Marshall ◽  
Patsy J. Thomas ◽  
Charles J. M. Stirling
Keyword(s):  
Leaving Group ◽  
Leaving Group Ability

Self-Assembled Monolayer Coatings on Amorphous Iron and Iron Oxide Nanoparticles:  Thermal Stability and Chemical Reactivity Studies

Langmuir ◽  
1997 ◽  
Vol 13 (23) ◽  
pp. 6151-6158 ◽  
Author(s):  
G. Kataby ◽  
T. Prozorov ◽  
Yu. Koltypin ◽  
H. Cohen ◽  
Chaim N. Sukenik ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Iron Oxide ◽  
Iron Oxide Nanoparticles ◽  
Chemical Reactivity ◽  
Oxide Nanoparticles ◽  
Self Assembled Monolayer ◽  
Amorphous Iron ◽  
Self Assembled

Mechanisms of aromatic nucleophilic substitution by the ambident thiocyanate ion

1973 ◽  
Vol 26 (2) ◽  
pp. 273 ◽  
Author(s):  
DE Giles ◽  
AJ Parker
Keyword(s):  
Nucleophilic Substitution ◽  
Transition States ◽  
Reactivity Ratio ◽  
Substitution Reactions ◽  
Aromatic Nucleophilic Substitution ◽  
Thiocyanate Ion ◽  
Sn2 Reactions ◽  
Leaving Group ◽  
Electrophilic Reactivity ◽  
Saturated Carbon Atom

Sulphur/nitrogen reactivity ratios in a series of aromatic nucleophilic substitution reactions of ambident thiocyanate ion have been determined. There are profound differences from the pattern found in SN2 reactions at a saturated carbon atom. Abnormal transition states, involving interactions between entering and leaving group, are likely in the bond-breaking step of the intermediate complex in reactions of thiocyanate ion with 1-fluoro-2,4-dinitrobenzene and with 2,4- dinitrophenyl 4-toluenesulphonate. The nitro-substituted aryl thiocyanates are shown to be tri-functional electrophiles, with reactive centres at aromatic carbon, at cyanide carbon, and at sulphur. Aryl 4-toluenesulphonates are bifunctional electrophiles with reactive centres at aryl carbon and sulphonyl sulphur. The site of attack by nucleophiles depends on the nature of the nucleophile. The sulphur/nitrogen reactivity ratio of ambident SCN-, and the electrophilic reactivity of tri- and bi-functional substrates, are in most instances consistent with the Hard and Soft Acids and Bases principle. Exceptions to the principle in some instances reveal differences between the SNAr and SN2 mechanisms, and in others indicate abnormal transition states.

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