Thermolysis kinetics

Meyer, L. U., De Meijere, A. A modern flow reactor for kinetic measurements of gas phase thermal rearrangements thermolysis kinetics of some new small ring compounds. Chem. Ber. 1977, 110, 2545-2560. 

TABLE 3.5. Thermolysis Kinetic Parameters of Transition Metal Unsaturated Carboxylates... 

A key issue in studies of thermolysis kinetics in hitherto unexplored systems, including Hf-containing polymers, is the optimization of the experimental procedure. Preliminary thermodynamic analysis of the Hf-C-H-0 system offers the possibility of establishing the temperature stability limits of HfC and HfO. Earlier, thermodynamic studies of the Hf-C-H-O system were carried out in relation to hafnium acetylacetonate, which is used to prepare HfC [33]. The most convenient approach to producing hafnium-containing nanocomposites with the aim of... 

The thermolysis kinetics of 1-12 have the following features in common In all of the samples, the gas evolution rate decreases steadily with time, the considerable gas evolution was observed already on the initial stage of the heating of sample. Figure 10.8 illustrates typical gas evolution kinetics during thermolysis. 

Thermolysis. Kinetic investigations of the thermolysis require dilution of HN3 by Ar in order to suppress possible contributions of the rapid and complex subsequent reactions [15]. The decrease of the induction period of the reaction with increasing temperature is more noticeable for mixtures at higher HN3 concentrations. Above 1250 K the induction period becomes short relative to the half-time of the reaction [10]. The decomposition is first order in both HN3 and Ar [15]. The results of shock-wave experiments are as follows ... 

Kinetic investigations of alkylchlorodiazirine thermolysis were carried out in the gas phase 70JCS(A)1916). Chloromethyldiazirine (232) decomposition follows first order kinetics giving nitrogen and vinyl chloride, easily interpretable as isomerization of a carbene. 

Both allylstannane transmetalation and thermolysis of homoallyl stannoxanes have been used to prepare 2-butenyltin halides as (E)j(Z) mixtures44-45. The reaction between 2-butenyl-(tributyl)stannane and dibutyltin dichloride initially provides dibutyl(l-methyl-2-propenyl)tin chloride as the kinetic product by an SE2 process, but this isomerizes under the reaction conditions to give a mixture containing the (Z)- and (E)-2-butenyl isomers46. 

The byproducts of decomposition of certain dialkyldiazcncs can be a concern. Consider the case of AIBN decomposition (Scheme 3.13). The major byproduct is the ketenimine (lO).61 100"102 This compound is itself thermally labile and reverts to cyanoisopropyl radicals at a rate constant similar lo that for AIBN thermolysis.59,60 102 This complicates any analysis of the kinetics of initiation/2,60... 

The volatile products of these processes have been identified and some insight has been gained into the kinetics and mechanism of the polymer thermolysis reactions. 

A kinetic study of thermolysis reactions of TV-crotyl substituted 1,2,4-triazoles was performed at temperatures in the range of 260-350 CC <00JHC1135>. Thermolysis of tetrazolo[l, 5- >]pyridazines, tetrazolo[l,5-a]pyrimidines and tetrazolo[l,5-a]pyridines allowed easy ring contraction to a facile preparation of cyanopyrazole heterocycles . 

Whether SnFLt is a symmetric or spherical top was discussed based on the rotational spectrum of the sixth stretching vibrational overtone, obtained by photoacoustic spectroscopy107. The IR band at vgn ]q 1844 cm-1 served to investigate the kinetics and mechanism of chemical vapour deposition of a thin tin layer, by thermolysis of trimethylstannane at 378-503 K108. 

In pentane, the distribution of 1,3-insertion product 25 to 1,2-Me shift product 26 is 91 9. Upon addition of 2-methyl-1-butene, the yield of 25 smoothly decreases (to 19% with 4 M alkene), but the yield of 26 is unaffected 1 Moreover, correlation of addn/l,3-CH insertion (to 25) for 18 is nicely linear. The simplest interpretation is that 25 comes directly from carbene 18, whereas the 1,2-Me shift product 26 comes from the excited diazirine.27 Interestingly, thermolysis of 24 at 79°C produces 90% of 25 and 10% of 26, but now the yields of both products smoothly decrease in the presence of an alkene. In thermolysis the (electronically) excited diazirine is unavailable, both 25 and 26 stem from the carbene, and their formation is suppressed by the alkene s interception of the carbene. A pyridine ylide kinetic study gave the 1,3-CH insertion rate constant (18 - 25) as 9.3 x 10s s"1.27-47... 

The positional selectivity on formation of the cydoadducts from 221 is less pronounced than that of the isobenzene 162, but it is the conjugated double of the allene moiety as well that predominantly undergoes the reaction. As demonstrated by the thermolysis of several products, these are formed from 221 under kinetic control. For example, on heating, the styrene adduct 240 and the furan adduct 231 rearranged virtually completely to 241 and 232, which are formally the cycloadducts to the non-conjugated double bond of the allene subunit of 221 [92, 137]. The cause of the selectivity may be the spin-density distribution in the phenylallyl radical entity of the diradical intermediates. 

A study of the kinetics and products of the thermolysis of a series of diaryl-phosphinic azides has been reported.119 Diethyl 1-diazomethylphosphonates undergo an aldol-type reaction with aldehydes to give l-diazo-2-hydroxyalkylphosphonates (152).120 Acidification of the diazophosphonates (153) possessing a chiral phosphorus centre yields mixtures of diastereoisomers (154) and epimers at C. For given R1 and R2, the reaction becomes increasingly stereoselective for X= OAc < Cl < OTs. It may be argued that protonation of (153) will yield a mixture of diastereoisomeric di-... 

Kinetic studies of the thermolysis of diazomethane were carried out by various authors. These experiments demonstrated that the decomposition of diazomethane was a first order reaction 41-43) Similar investigations of the p5n olysis of diphenyl-diazomethane in xylene or 1-methylnaphthalene also showed that the disappearance of diphenyl-diazomethane is a first order process. It may be concluded that a free carbene is involved in these reactions, in accordance with the following scheme ). 

A number of reports on the thermal decomposition of peroxides have been published. The thermal decompositions of f-butyl peroxyacetate and f-butyl peroxypivalate, of HCOH and a kinetic study of the acid-induced decomposition of di-f-butyl peroxide in n-heptane at high temperatures and pressures have been reported. Thermolysis of substituted f-butyl (2-phenylprop-2-yl) peroxides gave acetophenone as the major product, formed via fragmentation of intermediate alkoxy radicals RCH2C(Ph)(Me)0. A study of the thermolysis mechanism of di-f-butyl and di-f-amyl peroxide by ESR and spin-trapping techniques has been reported. The di-f-amyloxy radical has been trapped for the first time. jS-Scission reaction is much faster in di-f-amyloxyl radicals than in r-butoxyl radicals. The radicals derived from di-f-butyl peroxide are more reactive towards hydrogen abstraction from toluene than those derived from di-f-amyl peroxide. 

The formation of cyclic nitrones (150) from pericyclic mechanism. Kinetic and computational studies have provided evidence for the involvement of a novel pseudo-pericyclic electrocyclization in the conversion of o-vinylphenyl isocyanates into quinolin-2-ones. " Such reactions have also provided evidence of torquoselectivity in a 6jt system. Hash vacuum thermolysis of triazoles (151) has been found to afford dihydroquinolines (155), presumably by generation of a-oxoketenimines (152) which can undergo a [1,5]-hydrogen shift to the o-quinoid imines (153)7(154) and subsequent electrocyclization (see Scheme 57). 

Polavatapu, et al. (128) have identified a VCD band near 12(X) cm in phenylcaibinols that correlates with configuration. Wieser and co-workers (129, 130) have recently reported FTIR-VCD spectra of chiral methyloxetan molecules. In the area of theoretical calculations, Lx>we, Stephens, and Segal (131, 132) have implemented the theory of Stephens (118) in calculations on trans-1,2,-dideuteriocyclopropane, tron5-l,2-dideuteriocyclobutane, and propylene oxide. For the latter two molecules, favorable agreement with experiment was found. The first application of VCD to kinetic analysis has also been reported for (1/ , 2R)-dideuteriocyclobutane thermolysis (133). 

Brief consideration will be given to NMR investigation of intermediates, products and kinetics of reactions. Alkylation, arylation, metalation, reaction with organometallics, thermolysis and thermal rearrangements, isomerisation and many other reactions such as the Wittig, Michaelis and Arbuzov reactions, which are typical of organophosphorus... 

Formation of cluster opened methano- and imino[60[fullerenes (fulleroids and azafUlleroids) Thermal [3+2]-cycloadditions ofdiazo compounds or azides leads to the formation of fulleropyrazolines or fullerotriazolines. Thermolysis of such adducts after extrusion of N2 affords as kinetic products the corresponding [5,6]-bridged methano and iminofullerenes with an intact 60 re-electron system and an open transannular bond (see Chapter 4) [88-91]. The corresponding [6,6]-bridged structures with 58 re-electrons and a closed transannular bond are formed only in traces. 

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