Pyrolysis mechanism for

An example of a retrograde aldol reaction (retroaldolization) is probably the pyrolytic decomposition of cellulose with formation of hydroxyacetaldehyde (see Section 7.2), Other mechanisms for pyrolysis of cellulose are also possible [3]. More paths for the same process is a common occurrence in pyrolysis, and more than one mechanism is frequently needed to explain the variety of reaction products. 

In order to reconcile to some degree the results cited here, the mechanism for pyrolysis of polypropylene needs to be considered. The mechanism commonly accepted is based on those proposed for the gas-phase degradation of simple hydrocarbons (19, 20). 

Vigure 6. Overall mechanism for pyrolysis including both gas-phase and surface reactions... 

The pyrolysis of acetic esters to give an alkene and acetic acid is thought to involve a planar transition state and cyclic redistribution of (4 + 2) electrons. Propose a mechanism for pyrolysis of the following ester. 

Barton and co-workers" performed flash vacuum pyrolysis (FVP) on trimethyl-silylvinylmethylchlorosilane (30), resulting in the production of trimethylchlorosi-lane (30%), trimethylvinylsilane (11.5%), and most interestingly, ethynylmethyl-silane (34, 11.9%). A proposed mechanism for the synthesis of 34 (Scheme 10) begins with the lo.ss of trimethylchlorosilane to form silylene 31, which can rearrange either to silaallene 32 or to silirene 33, both of which can lead to the isolated ethynylsilane. 

Intensification can be achieved using this approach of combination of cavitation and advanced oxidation process such as use of hydrogen peroxide, ozone and photocatalytic oxidation, only for chemical synthesis applications where free radical attack is the governing mechanism. For reactions governed by pyrolysis type mechanism, use of process intensifying parameters which result in overall increase in the cavitational intensity such as solid particles, sparging of gases etc. is recommended. 

Houser and Lee [J. Phys. Chem., 71 (3422), 1967] have studied the pyrolysis of ethyl nitrate using a stirred flow reactor. They iiave proposed the following mechanism for the reaction. 

A chain mechanism for the pyrolysis of H202 has been proposed by Satterfield and Stein14 to account for the order observed by them. They include the reaction H02+H202 - H20+0H+02 in the above scheme. However, other investigators have failed to observe the order reaction. Furthermore, the usual tests, addition of inhibitors etc., do not indicate the occurrence of a chain reaction. 

The mechanism for the photolysis of diethyl mercury is identical to that for the pyrolysis88, 90. The reaction of C2H5 with diethyl mercury, which apparently was of no importance under the conditions used in the pyrolysis studies, is also insignificant over the temperature range 25-75 °C. The photolysis produces ethyl radicals which initially have about 31 kcal.mole-1 excess energy so that the C4/C2 ratio is dependent on the surface/volume ratio and on the total pressure in the system. At 25 °C with essentially thermalized radicals (200 torr Ne added) CJC2 20 while at 20 torr CJC2 3. 

The pyrolysis was studied using pressure of 50-200 torr over 350-410 °C in silicon and platinum vessels. The reaction in the platinum vessel was complex and will not be discussed. A probable mechanism for that in the silicon vessel is... 

Rice—Herzfeld mechanism for alkane pyrolysis is an example which, in its... 

Rate constants for elementary reactions involving tin compounds are even rarer. In an important recent investigation, Takahashi et al. performed shock-tube measurements and RRKM analysis from which they obtained rate constants for several important reactions involved in mechanism for SnCU pyrolysis [50] ... 

Taylor in 1925 demonstrated that hydrogen atoms generated by the mercury sensitized photodecomposition of hydrogen gas add to ethylene to form ethyl radicals, which were proposed to react with H2 to give the observed ethane and another hydrogen atom. Evidence that polymerization could occur by free radical reactions was found by Taylor and Jones in 1930, by the observation that ethyl radicals formed by the gas phase pyrolysis of diethylmercury or tetraethyllead initiated the polymerization of ethylene, and this process was extended to the solution phase by Cramer. The mechanism of equation (37) (with participation by a third body) was presented for the reaction, - which is in accord with current views, and the mechanism of equation (38) was shown for disproportionation. Staudinger in 1932 wrote a mechanism for free radical polymerization of styrene,but just as did Rice and Rice (equation 32), showed the radical attack on the most substituted carbon (anti-Markovnikov attack). The correct orientation was shown by Flory in 1937. In 1935, O.K. Rice and Sickman reported that ethylene polymerization was also induced by methyl radicals generated from thermolysis of azomethane. 

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