Model-free kinetic determination of pre-exponential factor and reaction mechanism in accelerating rate calorimetry

2021 ◽  
pp. 178983
Author(s):  
Jiong Ding ◽  
Xingci Zhang ◽  
Dongfang Hu ◽  
Shuliang Ye ◽  
Juncheng Jiang
1984 ◽  
Vol 49 (7) ◽  
pp. 1577-1591 ◽  
Author(s):  
Jaromír Mindl ◽  
Vojeslav Štěrba ◽  
Vladimír Kadeřábek ◽  
Jiří Klicnar

The hydrolysis of benzhydryl N-arylthiocarbamates proceeds by the ElcB mechanism. The reaction mechanism of S-benzhydryl N-arylthiocarbamates has been determined by trapping the reactive intermediate phenyl isocyanate (as N-phenyl-N'-mopholinourea) and by following the substitutent effects in benzene ring of the benzhydryl group. The hydrolysis mechanism of O-benzhydryl N-arylthiocarbamates has been confirmed by spectral and kinetic determination of phenyl isothiocyanate. The hydrolysis of the primary formed phenyl isothiocyanate is almost 10 times slower than that of the starting thiocarbamate. With O-benzhydryl N-arylthiocarbamates at pH below 9 there takes place, at first, a rapid rearrangement to S-benzhydryl N-arylthiocarbamates, and benzhydrol is the reaction product. The rearrangement rate is pH independent. At pH above 11.5 the hydrolysis of O-benzhydryl N-arylthiocarbamates is much faster than the rearrangement, and thiobenzhydrol is the reaction product. Using the deuterated derivatives, the IR spectra of carbamates and thiocarbamates have been interpreted with respect to coupled vibrations of carbamic, thiocarbamic, and dithiocarbamic groups.


Author(s):  
John Ross ◽  
Igor Schreiber ◽  
Marcel O. Vlad

In a chemical system with many chemical species several questions can be asked: what species react with other species: in what temporal order: and with what results? These questions have been asked for over one hundred years about simple and complex chemical systems, and the answers constitute the macroscopic reaction mechanism. In Determination of Complex Reaction Mechanisms authors John Ross, Igor Schreiber, and Marcel Vlad present several systematic approaches for obtaining information on the causal connectivity of chemical species, on correlations of chemical species, on the reaction pathway, and on the reaction mechanism. Basic pulse theory is demonstrated and tested in an experiment on glycolysis. In a second approach, measurements on time series of concentrations are used to construct correlation functions and a theory is developed which shows that from these functions information may be inferred on the reaction pathway, the reaction mechanism, and the centers of control in that mechanism. A third approach is based on application of genetic algorithm methods to the study of the evolutionary development of a reaction mechanism, to the attainment given goals in a mechanism, and to the determination of a reaction mechanism and rate coefficients by comparison with experiment. Responses of non-linear systems to pulses or other perturbations are analyzed, and mechanisms of oscillatory reactions are presented in detail. The concluding chapters give an introduction to bioinformatics and statistical methods for determining reaction mechanisms.


Author(s):  
Martina Maria Calvino ◽  
Lorenzo Lisuzzo ◽  
Giuseppe Cavallaro ◽  
Giuseppe Lazzara ◽  
Stefana Milioto

AbstractIn this paper, films based on sustainable polymers with variable charge have been investigated by non-isothermal thermogravimetry in order to predict their lifetime, which is a key parameter for their potential use in numerous technological and biomedical applications. Specifically, chitosan has been selected as positively charged biopolymer, while alginate has been chosen as negatively charged biopolymer. Among non-ionic polymers, methylcellulose has been investigated. Thermogravimetric measurements at variable heating rates (5, 10, 15 and 20 °C min−1) have been performed for all the polymers to study their degradation kinetics by using isoconversional procedures combined with ‘Master plot’ analyses. Both integral (KAS and Starink methods) and differential (Friedman method) isoconversional procedures have shown that chitosan possesses the highest energetic barrier to decomposition. Based on the Master plot analysis, the decomposition of ionic polymers can be described by the R2 kinetic model (contracted cylindrical geometry), while the degradation of methylcellulose reflects the D2 mechanism (two-dimensional diffusion). The determination of both the decomposition mechanism and the kinetic parameters (activation energy and pre-exponential factor) has been used to determine the decay time functions of the several biopolymers. The obtained insights can be helpful for the development of durable films based on sustainable polymers with variable electrostatic characteristics. Graphical abstract


1992 ◽  
Vol 263 (1-2) ◽  
pp. 143-146 ◽  
Author(s):  
C. Sanchez-Pedreño ◽  
J.A. Ortuño ◽  
D. Martinez

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