Analysis of the Mechanism of N-t-Butyl-2-Benzothiazole Sulfenamide Accelerated Sulfur Vulcanization of cis-Polyisoprene

1994 ◽  
Vol 67 (2) ◽  
pp. 348-358 ◽  
Author(s):  
M. R. Krejsa ◽  
J. L. Koenig ◽  
A. B. Sullivan
Keyword(s):  
Double Bond ◽  
Network Analysis ◽  
Mechanistic Studies ◽  
Exchange Reactions ◽  
Methyl Carbon ◽  
Double Bond Migration ◽  
Sulfur Vulcanization ◽  
Cis And Trans ◽  
Vulcanization Process

Abstract Results of previously published work involving network analysis and accelerator intermediate analysis of cis-polyisoprene were compared to help correlate and rationalize network/chemistry relationships. Both classical chemical probe network analysis and further NMR measurements (DEPT analysis) were used as necessary to verify NMR peak assignments. Furthermore, samples of the conventional formulation were vulcanized in the absence of zinc oxide and stearic acid to help elucidate the role of zinc in the vulcanization process. Polysulfidic dibenzothiazole accelerator intermediates were proposed to produce allylic substituted cis-polysulfides both with and without double bond migration, while zinc polysulfidic dibenzothiazole accelerator intermediates were proposed to produce allylic cis and trans polysulfides substituted structures with no double bond migration. Polysulfidic substitution on the isoprene methyl carbon was shown to result from exchange reactions during network maturation. The network-chemistry relationships were compared with earlier mechanistic studies and several points of agreement were noted.

Activators in Accelerated Sulfur Vulcanization

2004 ◽  
Vol 77 (3) ◽  
pp. 512-541 ◽  
Author(s):  
Geert Heideman ◽  
Rabin N. Datta ◽  
Jacques W. M. Noordermeer ◽  
Ben van Baarle
Keyword(s):  
Reaction Mechanisms ◽  
Model Compound ◽  
Background Information ◽  
Zinc Compounds ◽  
Chemical Mechanisms ◽  
Sulfur Vulcanization ◽  
Multifunctional Additives ◽  
Vulcanization Process

Abstract This review provides relevant background information about the vulcanization process, as well as the chemistry of thiuram- and sulfenamide-accelerated sulfur vulcanization with emphasis on the role of activators, to lay a base for further research. It commences with an introduction of sulfur vulcanization and a summary of the reaction mechanisms as described in literature, followed by the role of activators, particularly ZnO. The various possibilities to reduce ZnO levels in rubber compounding, that have been proposed in literature, are reviewed. A totally different approach to reduce ZnO is described in the paragraphs about the various possible roles of multifunctional additives (MFA) in rubber vulcanization. Another paragraph is dedicated to the role of amines in rubber vulcanization, in order to provide some insight in the underlying chemical mechanisms of MFA systems. Furthermore, an overview of Model Compound Vulcanization (MCV) with respect to different models and activator/accelerator systems is given. In the last part of this review, the various functions of ZnO in rubber are summarized. It clearly reveals that the role of ZnO and zinc compounds is very complex and still deserves further clarification.

Sulfur Vulcanization of Simple Model Olefins, Part V: Double Bond Isomerization during Accelerated Sulfur Vulcanization as Studied by Model Olefins

1997 ◽  
Vol 70 (1) ◽  
pp. 106-119 ◽  
Author(s):  
P. Versloot ◽  
J. G. Haasnoot ◽  
P. J. Nieuwenhuizen ◽  
J. Reedijk ◽  
M. van Duin ◽  
...  
Keyword(s):  
Double Bond ◽  
Isomerization Reaction ◽  
Radical Mechanism ◽  
Formation Mechanisms ◽  
Molecular Models ◽  
Tetramethylthiuram Disulfide ◽  
Alkyl Substitution ◽  
Sulfur Vulcanization ◽  
The One ◽  
Vulcanization Process

Abstract The sulfur vulcanization of unsaturated rubber has been studied with the use of various olefins as simple, low-molecular models. By treatment of these olefins with a mixture of zinc oxide, sulfur, and tetramethylthiuram disulfide (TMTD) at 140 °C, a mixture of dialkenyl sulfides is obtained mimicking crosslinked rubber. Isomerization of the double bond may take place during this reaction, depending on the olefin used. The position of the double bond is on the one hand determined by crosslink formation mechanisms, and on the other hand by isomerization, which takes place at higher temperatures. The position of the equilibrium between isomeric alkenyl sulfides is determined by the increased stability of the sulfide which in itself results from an increased degree of alkyl substitution at the unsaturation. Due to the isomerization reaction, at higher temperatures no mechanism for crosslink formation can be discerned. At room temperature, however, a radical mechanism appears to be predominant during the vulcanization process.

Solid-State C-13 NMR Studies of Vulcanized Elastomers X. N-t-Butyl-2-Benzothiazole Sulfenamide Accelerated Sulfur Vulcanization of cis-Polyisoprene at 75.5 MHz

1992 ◽  
Vol 65 (2) ◽  
pp. 427-443 ◽  
Author(s):  
M. R. Krejsa ◽  
J. L. Koenig
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Chain Scission ◽  
Sulfur Concentration ◽  
Nmr Studies ◽  
Double Bond Migration ◽  
Sulfur Vulcanization ◽  
Equilibrium Swelling ◽  
Cis And Trans ◽  
Good Agreement

Abstract Accelerated sulfur vulcanized cis-polyisoprene was analyzed using C-13 solid-state NMR to determine the chemical microstructure of the network. Three formulations were analyzed consisting of varying accelerator/sulfur ratios. All formulations yielded similar network structures, but the amount of sulfurization varied with sulfur concentration. At low percent cure, only polysulfidic A-type cis-structures were found. For longer cure times, the A-type structures shortened to monosulfldic, and B-type polysulfidic structures, both cis and trans, were formed. The amount of trans-sulfurized product was constant with cure once this resonance appeared. No isomerization, chain scission, saturation, or double bond migration was detected. The NMR measurements appeared to show fairly good agreement with equilibrium swelling measurements.

The role of the functional group in double bond migration in allylic systems catalysed by ruthenium hydride complexes

2006 ◽  
Vol 253 (1-2) ◽  
pp. 132-146 ◽  
Author(s):  
S. Krompiec ◽  
N. Kuźnik ◽  
M. Krompiec ◽  
R. Penczek ◽  
J. Mrzigod ◽  
...  
Keyword(s):  
Double Bond ◽  
Functional Group ◽  
Double Bond Migration ◽  
Ruthenium Hydride ◽  
Hydride Complexes

The Role of the Functional Group in Double Bond Migration of Allylic Systems Catalyzed by Ruthenium Hydride Complexes

ChemInform ◽  
2007 ◽  
Vol 38 (25) ◽  
Author(s):  
S. Krompiec ◽  
N. Kuznik ◽  
M. Krompiec ◽  
R. Penczek ◽  
J. Mrzigod ◽  
...  
Keyword(s):  
Double Bond ◽  
Functional Group ◽  
Double Bond Migration ◽  
Ruthenium Hydride ◽  
Hydride Complexes

Solid-State C-13 NMR Studies of Vulcanized Elastomers XIII. TBBS Accelerated, Sulfur-Vulcanization of Carbon Black Filled Natural Rubber

1995 ◽  
Vol 68 (4) ◽  
pp. 551-562 ◽  
Author(s):  
Makio Mori ◽  
Jack L. Koenig
Keyword(s):  
Double Bond ◽  
Solid State ◽  
Carbon Black ◽  
Natural Rubber ◽  
Main Chain ◽  
Chain Scission ◽  
Nmr Studies ◽  
Double Bond Migration ◽  
Sulfur Vulcanization ◽  
Basic Network

Abstract Solid state C-13 NMR has been used to compare the chemistry of accelerated vulcanization of natural rubber using N-t-butyl-2-benzothiazole sulfenamide in the presence and absence of carbon black. The carbon black filler has an influence on the vulcanization chemistry in addition to its accepted role in reinforcment and stabilization. The basic network structure formation is modified to the extent that crosslink desulfurization from poly to monosulflde structures occurs earlier in the cure in the presence of carbon black. No main chain scission or double bond migration was detected.

Synthetic and Mechanistic Studies of a Versatile Heteroaryl Thioether Directing Group for Pd(II) Catalysis

2019 ◽  
Author(s):  
Andrew Romine ◽  
Kin Yang ◽  
Malkanthi Karunananda ◽  
Jason Chen ◽  
Keary Engle
Keyword(s):  
Mechanistic Studies ◽  
Salvianolic Acid ◽  
Wide Range ◽  
Computational Data ◽  
Synthetic Utility ◽  
Directing Group ◽  
High Yields ◽  
Julia Olefination ◽  
Reaction Progress Kinetic Analysis

A weakly coordinating monodentate heteroaryl thioether directing group has been developed for use in Pd(II) catalysis to orchestrate key elementary steps in the catalytic cycle that require conformational flexibility in a manner that is difficult to accomplish with traditional strongly coordinating directing groups. This benzothiazole thioether, (BT)S, directing group can be used to promote oxidative Heck reactivity of internal alkenes providing a wide range of products in moderate to high yields. To demonstrate the broad applicability of this directing group, arene C–H olefination was also successfully developed. Reaction progress kinetic analysis provides insights into the role of the directing group in each reaction, which is supplemented with computational data for the oxidative Heck reaction. Furthermore, this (BT)S directing group can be transformed into a number of synthetically useful functional groups, including a sulfone for Julia olefination, allowing it to serve as a “masked olefin” directing group in synthetic planning. In order to demonstrate this synthetic utility, natural products (+)-salvianolic acid A and salvianolic acid F are formally synthesized using the (BT)S directed C–H olefination as the key step.

Sign in / Sign up

Export Citation Format

Share Document