Pressure-induced phase transition of hydrogen sulfide at low temperature: Role of the hydrogen bond and short S-S contacts

2001 ◽  
Vol 64 (10) ◽  
Author(s):  
Takashi Ikeda
Keyword(s):  
Phase Transition ◽  
Hydrogen Bond ◽  
Hydrogen Sulfide ◽  
Low Temperature

The Role of Free Radicals in Low Temperature Vulcanization of Butadiene Rubber

1960 ◽  
Vol 33 (1) ◽  
pp. 199-207
Author(s):  
B. A. Dogadkin ◽  
E. N. Belyaeva
Keyword(s):  
Hydrogen Sulfide ◽  
Low Temperature ◽  
Benzoyl Peroxide ◽  
Spectroscopic Analysis ◽  
Elementary Sulfur ◽  
Butadiene Rubber ◽  
Radical Chain ◽  
Considerable Loss ◽  
Chain Interaction

Abstract 1. Elementary sulfur, liberated in the nascent state at room temperature in the reactions of MBTS with H2S, of benzoyl peroxide with H2S and SO2 with H2S, does not bring about vulcanization of butadiene rubber. In the case of the system MBTS/H2S we observe combination of sulfur in amounts 1.2 to 1.6% to a small portion of the rubber, which does not lead to structurization. The main part of the rubber (about 90% by weight) does not, according to spectroscopic analysis, alter. The combination of sulfur with rubber observed in this case takes place, apparently, according to an ionic mechanism. 2. Low-temperature vulcanization (structurization) of rubber by the system MBTS/H2S becomes apparent with prior irradiation of solutions of rubber containing disulfide with diffuse or ultraviolet light. The rate of structurization depends upon the duration of irradiation and is governed by the interaction with the H2S of the polymeric rubber radicals which are formed as a result of the dehydrogenation of the rubber by the benzothiazolyl radicals which are formed in the photodissociation of the disulfide. 3. Structurization of rubber by the system benzoyl peroxide/hydrogen sulfide is observed in the presence of an amine, in particular PBNA, necessary for the formation of free benzoate radicals as a result of the reaction of the peroxide with the amine. The peroxide in the present case acts similarly to the benzothiazolyl radicals in the case of the system MBTS/H2S. 4. Peachey type low-temperature vulcanization (SO2/H2S) proceeds in the presence of the peroxides of the rubber itself. Prior heating of the solutions of rubber upsets structurization. 5. In the vulcanization of rubber by the systems MBTS/H2S and benzoyl peroxide/hydrogen sulfide we observe combination of sulfur with the rubber in amounts of 0.6 to 0.7% and a considerable loss of double bonds, reaching 60% for 1:4 type bonds and 75% for 1:2 type bonds. 6. Radical chain interaction schemes are put forward for the processes of low-temperature structurization (vulcanization) of rubber under the action of the systems MBTS/H2S, benzoyl peroxide/hydrogen sulfide and SO2/H2S. 7. The reaction of benzoyl peroxide with PBNA is studied. A new compound, O-benzoyl-N-phenyl-N-2-naphthylhydroxylamine, is obtained, which is a powerful inhibitor of rubber oxidation.

scholarly journals Selected solid-state behaviour of three di-tert-butyl-substituted N-salicylideneaniline derivatives: temperature-induced phase transitions and chromic behaviour

2021 ◽  
Vol 77 (10) ◽  
pp. 659-667
Author(s):  
Helen E. Mason ◽  
Judith A. K. Howard ◽  
Hazel A. Sparkes
Keyword(s):  
Phase Transition ◽  
Hydrogen Bond ◽  
Phase Transitions ◽  
Solid State ◽  
Low Temperature ◽  
Schiff Bases ◽  
Photochromic Properties ◽  
Keto Form ◽  
Single Crystal Structures ◽  
State Behaviour

The synthesis, single-crystal structures and chromic behaviour of three related Schiff bases, namely, (E)-2,4-di-tert-butyl-6-{[(4-fluorophenyl)imino]methyl}phenol, C21H26FNO, 1, (E)-2,4-di-tert-butyl-6-{[(4-chlorophenyl)imino]methyl}phenol, C21H26ClNO, 2, and (E)-6-{[(4-bromophenyl)imino]methyl}-2,4-di-tert-butylphenol, C21H26BrNO, 3, are reported. Two polymorphs of 1 were obtained, which were found to have different photochromic properties. Schiff bases 2 and 3 were found to be isostructural and underwent a phase transition upon cooling which was attributed to the dynamic disorder in one of the tert-butyl groups resolving at low temperature. All of the structures were found to exist in the enol rather than the keto form based on the C—O(H) and imine C=N bond lengths, and contained an intramolecular O—H...N hydrogen bond alongside weaker intermolecular C—H...O contacts.

Sign in / Sign up

Export Citation Format

Share Document