The Chemistry of Vulcanization. I. Diphenylmethane as a Model of Rubber Hydrocarbon for Its Reaction with Sulfur

1958 ◽  
Vol 31 (4) ◽  
pp. 762-786 ◽  
Author(s):  
Jitsuo Tsurugi
Keyword(s):  
Reaction Mechanism ◽  
Model Compound ◽  
Chemical Investigation ◽  
Hydrocarbon Radical ◽  
Reaction Products ◽  
Primary Reaction ◽  
Secondary Product ◽  
Model Compounds ◽  
Vast Number ◽  
Produce Water

Abstract Following the discovery of vulcanization of rubber by Goodyear, a vast number of experiments and speculations have been carried out, but the final clarification of the mechanism of vulcanization and acceleration has remained unsettled. Overemphasis of physical and technological criteria in the investigation of vulcanization may have contributed to the failure to attach importance to the purely chemical investigation. In fact rubber vulcanizates defy chemical investigation because they are insoluble and infusible. However, in 1947 Farmer and collaborators, using olefinic substances such as cyclohexene, dihydromyrcene and squalene as model compounds, proposed a new theory on the vulcanization of rubber by sulfur. According to them α-methylenic hydrogen adjacent to olefinic double bonds is attacked by sulfur, and a hydrocarbon radical is formed. Then this radical couples with the diradical ⋅Sx⋅ and this leads to polysulfides as primary reaction products. Farmer's theory laid the ground work for the chemical investigation of vulcanization but the reaction of olefins with sulfur is too complex to indicate the reaction mechanism. Diphenylmethane (DPM) contains α-methylenic hydrogen (to a benzene ring) and may be expected to react with relative readiness. Moreover the reaction of DPM with molecular oxygen is already reported to produce water, diphenylmethyl hydroperoxide, tetraphenylethane and benzophenone. It is expected then that when DPM reacts with sulfur, it should give the thio analogs of these compounds. Since the reaction and reaction products of sulfur with DPM are considerably less complex than those with olefinic substances, the reaction mechanism should be elucidated by using the simpler hydrocarbon as a model compound. Comparative studies of the reaction with and without accelerator will present the key to the mechanism and theory of acceleration. As fundamental studies of rubber vulcanization as well as acceleration the following are the two objects of this paper. The first is the reaction mechanism of DPM with sulfur at 180° C and the second is the pyrolysis of the primary product (dibenzhydryl polysulfide) to the secondary product (thiobenzophenone) at the same temperature. Investigations on the reaction of DPM with sulfur in the presence of accelerators will be reported in other papers of this series.

Study on the Formation of Ethyl Levulinate from Wheat Straw Based on a Model Compound

2020 ◽  
Vol 14 (2) ◽  
pp. 273-279
Author(s):  
Zhiyong Chen ◽  
Qian Guan ◽  
Haiyan Xu ◽  
Tingzhou Lei ◽  
Lu Lin ◽  
...  
Keyword(s):  
Reaction Time ◽  
Wheat Straw ◽  
Microcrystalline Cellulose ◽  
Model Compound ◽  
Cellulose Degradation ◽  
Biomass Conversion ◽  
Reaction Products ◽  
Model Compounds ◽  
Ethyl Levulinate ◽  
Change Trend

Glucose and microcrystalline cellulose were selected as model compounds to investigate the formation of ethyl levulinate (EL). Optimal glucose and microcrystalline cellulose transformation conditions resulted in yields of 41.05 wt.% and 38.56 wt.% for EL, 0.73 wt.% and 2.63 wt.% for ethyl-glucoside (EG), 0.42 wt.% and 0.36 wt.% for 5-hydroxymethylfurfural (HMF), and 2.18 wt.% and 2.16 wt.% for 5-ethoxy methyl furfural (EMF), respectively. Increasing the reaction time and temperature resulted in an optimized yield of EL. These increases also resulted in decreased EG and EMF yield, and the change trend of HMF was not significant. EMF, HMF, and EG are intermediates in the formation of EL. Finally, we concluded that biomass conversion occurs first through cellulose degradation to glucose followed by the production of EG through alcoholysis and hydrolysis and dehydration of the reaction products to produce EL.

Study of kinetics of reaction of lignin model compounds with propylene oxide

Holzforschung ◽  
2008 ◽  
Vol 62 (2) ◽  
pp. 169-175 ◽  
Author(s):  
Krishna K. Pandey ◽  
Tapani Vuorinen
Keyword(s):  
Chemical Reaction ◽  
Propylene Oxide ◽  
Aqueous Media ◽  
Reaction Products ◽  
Model Compounds ◽  
Rapid Reduction ◽  
Visible Absorption ◽  
Lignin Model Compounds ◽  
Lignin Model ◽  
Kinetics Of

Abstract The etherification of phenolic groups has been found to inhibit photodegradation in wood and lignin rich pulps. The precise understanding of kinetics of chemical reaction between lignins or their model compounds and the etherifying agent is the first step for developing a viable modification procedure. In this study, we have investigated the reaction of lignin model compounds (namely, phenol and guaiacol) with propylene oxide in aqueous media. The kinetics of etherification reaction was studied under varying pH conditions in the temperature range 30–60°C. The etherified reaction products were characterized by gas chromatogram-mass spectrum (GC-MS). The extent of etherification of phenols and the rate of chemical reaction was followed by UV-Visible absorption spectroscopy. The reaction between lignin model compounds and propylene oxide was indicated by a rapid reduction in the absorbance accompanied by the development of a new band corresponding to etherified products. The reaction kinetics was investigated at pH ∼12 under the condition of excess concentration of propylene oxide. The reaction followed first order kinetics and rate constants increased linearly with an increase in the temperature and concentration of propylene oxide. The MS fragment data of reaction product support the proposed reaction scheme. The activation energy of the reaction of propylene oxide with phenol and guaiacol, calculated with the Arrhenius equation, was 56.2 kJ mol-1 and 45.4 kJ mol-1, respectively.

Halogenation of Butyl Rubber—A Model Compound Approach

1984 ◽  
Vol 57 (2) ◽  
pp. 275-283 ◽  
Author(s):  
R. Vukov
Keyword(s):  
Model Compound ◽  
Product Distribution ◽  
Butyl Rubber ◽  
Methyl Groups ◽  
Reaction Site ◽  
Model Compounds ◽  
Reaction Conditions ◽  
Basic Study ◽  
Rubber Model ◽  
Trisubstituted Alkenes

Abstract The study of the halogenation behavior of butyl rubber model compounds has brought about a better understanding of the behavior of these systems. It has been established that the presence of methyl groups, in a position B to the reaction site in the butyl rubber model compound, profoundly influences the course of halogenation. Due to the steric hindrance imposed by these groups, both the products of chlorination and bromination deviate from patterns typical of other trisubstituted alkenes. In the case of chlorination, this deviation is demonstrated by the absence of addition products of chlorine across the double bond. In the case of bromination reactions, the change in product distribution is even more dramatic. Thus, substitution products normally not observed in bromination reactions of other trisubstituted alkenes become predominant products found in yields of between 70–90% depending on the precise reaction conditions. The behavior of the butyl model compound appears to be entirely consistent with the behavior of butyl rubber itself; the model compound approach is therefore a valuable tool for use in the basic study of this type of system.

Quantum-Chemical Investigation of Reaction Mechanism of 2-R-4-Oxo-5,6-Benzo-1,3,2-Dioxaphosphorinanes with Chloral and Fluoral

1999 ◽  
Vol 147 (1) ◽  
pp. 265-265 ◽  
Author(s):  
Roza M. Aminova ◽  
Grigory A. Shamov ◽  
Vladimir B. Mushkin ◽  
Vladimir F. Mironov ◽  
Alexander I. Konovalov ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Quantum Chemical ◽  
Chemical Investigation ◽  
Quantum Chemical Investigation

Fast and automated identification of reactions with low barriers: the decomposition of 3-hydroperoxypropanal

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Mads Koerstz ◽  
Maria H. Rasmussen ◽  
Jan H. Jensen
Keyword(s):  
Reaction Mechanism ◽  
Systematic Approach ◽  
Transition States ◽  
Semiempirical Methods ◽  
Reaction Products ◽  
Reaction Energy ◽  
Automated Identification ◽  
Reaction Discovery ◽  
Systematic Enumeration ◽  
Computational Resources

We show how fast semiempirical QM methods can be used to significantly decrease the computational expense for automated reaction mechanism discovery, using two different method for generating reaction products: graph-based systematic enumeration of all possible products and the meta-dynamics approach by Grimme (J. Chem. Theory. Comput. 2019, 15, 2847). We test the two approaches on the low-barrier reactions of 3-hydroperoxypropanal, which have been studied by a large variety of reaction discovery approaches and therefore provides a good benchmark. By using PM3 and GFN2-xTB for reaction energy and barrier screening the systematic approach identifies 64 reactions (out of 27,577 possible reactions) for DFT refinement, which in turn identifies the three reactions with lowest barriers plus a previously undiscovered reaction. With optimized hyperparameters meta-dynamics followed by PM3/GFN2-xTB-based screening identifies 15 reactions for DFT refinement, which in turn identifies the three reactions with lowest barrier. The number of DFT refinements can be further reduced to as little as six for both approaches by first verifying the transition states with GFN1-xTB. The main conclusion is that the semiempirical methods are accurate and fast enough to automatically identify promising candidates for DFT refinement for the low barrier reactions of 3-hydroperoxypropanal in about 15-30 minutes using relatively modest computational resources.

scholarly journals βγ-Crystallination Endows a Novel Bacterial Glycoside Hydrolase 64 with Ca2+-Dependent Activity Modulation

2019 ◽  
Vol 201 (23) ◽  
Author(s):  
Bal Krishnan ◽  
Shanti Swaroop Srivastava ◽  
Venu Sankeshi ◽  
Rupsi Garg ◽  
Sudhakar Srivastava ◽  
...  
Keyword(s):  
Glycoside Hydrolase ◽  
Domain Architecture ◽  
Enzyme Reaction ◽  
Structural Features ◽  
Clostridium Beijerinckii ◽  
Biofuel Production ◽  
Carbohydrate Binding ◽  
Reaction Products ◽  
Vast Number ◽  
Content Type

ABSTRACT The prokaryotic βγ-crystallins are a large group of uncharacterized domains with Ca2+-binding motifs. We have observed that a vast number of these domains are found appended to other domains, in particular, the carbohydrate-active enzyme (CAZy) domains. To elucidate the functional significance of these prospective Ca2+ sensors in bacteria and this widespread domain association, we have studied one typical example from Clostridium beijerinckii, a bacterium known for its ability to produce acetone, butanol, and ethanol through fermentation of several carbohydrates. This novel glycoside hydrolase of family 64 (GH64), which we named glucanallin, is composed of a βγ-crystallin domain, a GH64 domain, and a carbohydrate-binding module 56 (CBM56). The substrates of GH64, β-1,3-glucans, are the targets for industrial biofuel production due to their plenitude. We have examined the Ca2+-binding properties of this protein, assayed its enzymatic activity, and analyzed the structural features of the β-1,3-glucanase domain through its high-resolution crystal structure. The reaction products resulting from the enzyme reaction of glucanallin reinforce the mixed nature of GH64 enzymes, in contrast to the prevailing notion of them being an exotype. Upon disabling Ca2+ binding and comparing different domain combinations, we demonstrate that the βγ-crystallin domain in glucanallin acts as a Ca2+ sensor and enhances the glycolytic activity of glucanallin through Ca2+ binding. We also compare the structural peculiarities of this new member of the GH64 family to two previously studied members. IMPORTANCE We have biochemically and structurally characterized a novel glucanase from the less studied GH64 family in a bacterium significant for fermentation of carbohydrates into biofuels. This enzyme displays a peculiar property of being distally modulated by Ca2+ via assistance from a neighboring βγ-crystallin domain, likely through changes in the domain interface. In addition, this enzyme is found to be optimized for functioning in an acidic environment, which is in line with the possibility of its involvement in biofuel production. Multiple occurrences of a similar domain architecture suggest that such a “βγ-crystallination”-mediated Ca2+ sensitivity may be widespread among bacterial proteins.

Product distributions and isotopic selectivities in ir multiphoton dissociation of pentafluoroiodoethane

1981 ◽  
Vol 59 (9) ◽  
pp. 1307-1310 ◽  
Author(s):  
E. Weinberg ◽  
M. Gauthier ◽  
P. A. Hackett ◽  
C. Willis
Keyword(s):  
Reaction Mechanism ◽  
Bond Cleavage ◽  
Thermal Dissociation ◽  
Infrared Multiphoton Dissociation ◽  
High Fluence ◽  
Reaction Products ◽  
Product Distributions ◽  
Multiphoton Dissociation

Infrared multiphoton dissociation of pentafluoroiodoethane leads to a complex array of reaction products. For photolysis in the v4 band the reaction mechanism involves C2F5—I bond cleavage followed by thermal dissociation of C2F5 radicals. For irradiation within the v3 band at high fluence, efficient secondary photolysis of C2F5 radicals is postulated. At lower fluences the dissociation is isotopically selective leading to C4F10 enriched in carbon-13.

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