Toluene carrier gas technique

The reaction of toluene is of interest as toluene has been used extensively in the toluene-carrier gas technique as a means of removing radicals from a reacting system (Szwarc, 1950). The results from the rotating cryostat show that n-heptyl radicals react with toluene at 77°K by abstracting a methyl hydrogen to give the benzyl radical. As expected, addition to the aromatic ring does not occur. 

They used toluene as carrier gas, and in addition found small amounts of methane and dibenzyl, presumably formed from toluene by the obvious reactions. Rebbert and Laidler state that they were using the toluene carrier gas technique of Szwarc, but in fact they were attempting to use it under conditions where it has no apparent advantage. Szwarc intended that the toluene should mop up the radicals formed by the initial bond fission of the compound under investigation, but clearly this did not happen at the temperatures used here (200-240° G). In fact, the recombination of methyl radicals, which requires no activation energy, is more likely to... 

Z)(G-H) in benzene has not been determined directly, but has been inserted here for purposes of comparison. It may be derived from the activation energy of the pyrolysis of bromobenzene, which has been shown by Szwarc and Williams to produce phenyl radicals and bromine atoms when the reaction is carried out using the toluene carrier gas technique. Z)(C6H5 -Br) is deduced to be 70 9 kcal, whence Z)(G6H5 -H) = 101 8 kcal, if the heat of formation of bromobenzene quoted by Szwarc and Williams is known to the required accuracy. 

The value of D C - Br) in methyl bromide has been determined by the pyrolysis method by Szwarc to be 67 kcal. The strength of the C - Br bond is such that it is particularly suited to pyrolyses using the toluene carrier gas technique, and Szwarc and his collaborators have exploited this property very thoroughly. It is convenient to list here the forty-odd values of D(G - Br) in various compounds obtained in this way. Ladacki and Szwarc 28 5 give the following values for the activation energy, frequency factor and rate constant of the pyrolysis. The constancy of the frequency factor over a... 

The principal experimental methods for measuring bond dissociation energies in polyatomic molecules have been described in detail by Cottrell (35). Two methods in particular have proved fruitful in recent years, namely the toluene carrier gas technique introduced by Szwarc (167) to investigate the unimolecular kinetics of pyrolytic decomposition reactions, and the electron impact method, as applied by Stevenson (165) and widely used since by several investigators. These methods do not usually give very sharp D values, and the number of well-authenticated ( 2... 

The pyroljrsis kinetics of only a few metal alkyls, other than those of mercury, have been investigated. Most of these were carried out in static systems, giving complex kinetics of dubious value for bond energy purposes. Recent studies by Price and Trotman-Dickenson 131-133) using the toluene carrier gas flow technique have proved more rewarding, providing the tabulated values. 

Three carboxylic acid bond fission reactions have been studied in the gas phase those of phenylacetic acid diphenylacetic acid , and peracetic acid . They were all studied by the toluene carrier technique and are therefore subject to the usual errors. In the phenyl and diphenylacetic acid decompositions, viz. 

Pyrolysis kinetics, including Toluene carrier tech Very low pressure pyrolysis (VLPP) Concentration of atoms, free radicals and molecules vs. time at different temperatures, using various detecting techniques, such as GC, HPLC, MS, FT-IR, UV/VIS, EPR, NMR, resonance fluorescence, chemiluminescence, and so on Species in gas and solution phase 1950SZW (1) 1973GOL/SPO (2) 1979ROS/KIN (3) 1982MCM/GOL... 

The currently most successfully commercialized route is based on the CVD technique. Catalyst particles, such as Fe, Ni, or other metal catalysts, are introduced onto a substrate which is placed in a furnace. The growth of filaments (carbon nanotubes) is most sensitive to the reaction conditions, such as the pressure of the vaporized carbon source (benzene, toluene, etc.), the purity and flow rate of the carrier gas, the residence time for thermal decomposition, and the temperature of the furnace. ... 

The gas-phase pyrolysis of dimethyl disulfide in the range 316-373 °C is apparently homogeneous, first order, and characterized by a reproducible induction period . The overall rate coefiicient is fc = 2x 10 exp(—45,000/RT) sec". The main products found were H2S, CH3SH, CS2 and various sulfides which were not characterized. Using the toluene flow carrier technique only traces of dibenzyl were found, and in addition to H2S and CH3SH, CH4, H2, C2H4 and C2H6 were formed. The kinetic data are incomplete, but it is probable that dimethyl disulfide decomposes mainly by a molecular mechanism... 

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