Sulfur Vulcanization and Oxidative Aging of Epoxidized Natural Rubber

1985 ◽  
Vol 58 (2) ◽  
pp. 243-257 ◽  
Author(s):  
I. R. Gelling ◽  
N. J. Morrison
Keyword(s):  
Thermal Decomposition ◽  
Natural Rubber ◽  
Ring Opening ◽  
Double Bonds ◽  
Oxidative Aging ◽  
The Poor ◽  
Ring Opening Reactions ◽  
Sulfur Vulcanization ◽  
Subsequent Effect ◽  
Acid Catalyzed

Abstract 1. Vulcanization by sulfur alone is faster and more efficient for ENR than for NR because isolated double bonds react more rapidly than contiguous double bonds. This vulcanization may be accelerated by sodium carbonate, which also protects the cured rubber against the subsequent effect of oxidative aging, and the scorch time may be increased by the addition of CTP. 2. The CBS-accelerated sulfur vulcanization of ENR is essentially similar to that of NR, although ENR reacts with MBT formed during the process. 3. The poor aging of sulfur vulcanizates of ENR is due to acid-catalyzed ring-opening reactions of the epoxide groups with the formation of ether crosslinks. The acids are produced by the thermal decomposition of oxidized sulfides. 4. The addition of a suitable base confers excellent resistance to oxidative aging upon conventional, semi-efficient, and efficient vulcanizates of ENR.

Recent Advances in Transition Metal Catalyzed C-H Functionalization Reactions Involving Aza/Oxabicyclic Alkenes

Synthesis ◽  
2021 ◽  
Author(s):  
Masilamani Jeganmohan ◽  
Pinki Sihag
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Ring Opening ◽  
Bond Activation ◽  
Considerable Progress ◽  
Double Bonds ◽  
Facial Selectivity ◽  
Ring Opening Reactions ◽  
Metal Catalyzed

Bicyclic alkenes, including Oxa- and azabicyclic alkenes can be readily activated by using transition-metal complexes with facial selectivity, because of the intrinsic angle strain on carbon-carbon double bonds of these unsymmetrical bicyclic systems. During last decades considerable progress has been done in the area of ring-opening of bicyclic strained ring by employing the concept of C-H activation. This Review comprehensively compiles the various C-H bond activation assisted reactions of oxa- and azabicyclic alkenes, viz., ring-opening reactions, hydroarylation as well as annulation reactions.

scholarly journals Acid Catalyzed Ring Opening Reactions of 6-Deoxy-9-deoxo-9a-aza-9a-homoerythromycin A 6,9-Cyclic Imino Ether.

1998 ◽  
Vol 51 (9) ◽  
pp. 893-896 ◽  
Author(s):  
GORJANA LAZAREVSKI ◽  
GABRIJELA KOBREHEL ◽  
AMALIJA NARANDA ◽  
ZRINKA BANIC-TOMIŠIC ◽  
BISERKA METELKO
Keyword(s):  
Ring Opening ◽  
Ring Opening Reactions ◽  
Acid Catalyzed

Mineral Sulfide as Index of Disulfide Cross-Bonding

1947 ◽  
Vol 20 (3) ◽  
pp. 649-663 ◽  
Author(s):  
C. M. Hull ◽  
S. R. Olsen ◽  
Wesley G. France
Keyword(s):  
Natural Rubber ◽  
Cross Linking ◽  
Diallyl Disulfide ◽  
Double Bonds ◽  
Metal Soap ◽  
Sulfide Production ◽  
Sulfur Vulcanization

Abstract 1. The mechanism proposed by Armstrong, Little, and Doak to explain sulfur vulcanization in the presence of metal soap was investigated in polyprene and simpler systems from the viewpoint of the inorganic sulfide produced and, in the case of polyprenes, of the accompanying modulus. 2. Dodecanethiol was found to react with sulfur and zinc soap to produce inorganic sulfide equivalent to the oxidation of 80 to 100 per cent of the thiol to disulfide ; with excess thiol substantially quantitative conversion of sulfur or of zinc soap to inorganic sulfide can be obtained. 3. Several simple olefins were found to react readily with sulfur and zinc soap under vulcanizing conditions. The reaction is promoted by M.B.T. On the basis of the mechanism assumed, the inorganic sulfide formed is sufficient to indicate extensive conversion of the olefin to a substituted diallyl disulfide. 4. Assuming the validity of the proposed mechanism, inorganic sulfide production indicates substantial disulfide cross-linking between α-carbon atoms in conventional cures with natural rubber, and appreciable, though relatively less, cross-bonding of this type in the case of GR-S. The smaller extent of this type of cross-linking with GR-S is believed to result from greater tendency on the part of this elastomer to add the intermediate mercapto compound to double bonds, as proposed in the first paper of this series.

scholarly journals SnCl4-catalyzed Solvent-free Acetolysis of 2,7-Anhydrosialic Acid Derivatives

2019 ◽  
Author(s):  
Kesatebrhan Haile Asressu ◽  
Cheng-Chung Wang
Keyword(s):  
Sialic Acid ◽  
Lewis Acids ◽  
Ring Opening ◽  
Building Blocks ◽  
Solvent Free ◽  
Biologically Active ◽  
Protecting Group ◽  
Free Ring ◽  
Ring Opening Reactions ◽  
Acid Catalyzed

Sialic acid-containing glycans are found in different sialic acid forms and a variety of glycosidic linkages in biologically active glycoconjugates. Hence, the preparation of suitably protected sialyl building blocks requires high attention in order to access glycans in pure form. In this line, various C-5 substituted 2,7-anhydrosialic acid derivatives bearing both electron donating and withdrawing protecting groups were synthesized and subjected to different Lewis acid-catalyzed solvent free ring opening reactions at room temperature in the presence of acetic anhydride. Among the various Lewis acids tested, the desired acetolysized products were obtained in moderate yields under a tin(IV) chloride catalysis system. Our methodology can be extended to regioselective protecting group installation and manipulation towards a number of thiosialoside and halide donors.

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