Propyl radicals from decomposition

Fig. 22. The yield of w-propyl radicals from the mercury-photosensitized decomposition of various propanes as a function of nitric oxide concentration. O—CjH8 ...

Propyl Radicals n-CsHi —> CHt + CJli. The models for n-propyl decomposition are given in Appendix III. eA was set at 3.1 as opposed to 1.6 kcal. for isopropyl formation. Values of kt are presented in Figure 12. Table XX summarizes some calculated values for various activation systems. H atom rupture is seen to be orders of magnitude slower than C—C bond rupture. Again, comparison may best be made with the results from chemical activation studies at 25°C. The observed values were ka0 = 8 X I07 and /bO0O = 18 X I07 sec.-1. The data fluctuated... 

Ethylene arises from the ethylidene radical. The decomposition of jec-propyl radical to give a hydrogen atom and propene is taken to be the major source of hydrogen atoms this process is not distinguishable from decomposition of i-butane to a hydrogen atom and a butyl radical followed by decomposition of the latter to a methyl radical and propene. 

In the above analysis of the iso-propyl radical decomposition the micro-canonical rate coefficients were obtained from an experimentally... 

Similarly, propene can form by decomposition of primary propyl radicals and secondary free radicals. Propane can form by propyl radicals abstracting hydrogen from another source. 

The kinetic isotope effect observed on the overall rates, ranging from 2.0 at 700 C to 1.5 at 800 C, was interpreted in terms of a free radical chain mechanism where a unimolecular decomposition of a hot n-propyl radical, produced by addition of H or D to propylene, plays a key role. The difference in the observed overall rates was mainly ascribed to that in steady state Concentrations of H and D which are produced, in part, through the reaction between allyl radical and H2 or D2. No appreciable difference between the decomposition rates of C3H7 and C3H6D was infered by RRKM theory. 

RRKM Calculation on the Unimolecular Decomposition of Hot n- and sec-Propyl Radicals. The basic concept of the computation is given elsewhere. (12) The thermochemical data were obtained from the literature. (13) Vibration models and the other parameters were mostly adopted from the work by Falconer, W.E. et al., (12) but with some modifications. The calculated rate constants shown below are at 998°K and atmospheric pressure. ... 

Copper and Silver.—Decomposition of 1-propenyl- and 2-butenyl-copper(i) and -silver(i) compounds to hexa-2,4-dienes occurs with retention of configuration. This indicates a non-radical mechanism, for intermediate vinylic radicals would be of very low configurational stability and would thus lead to extensive isomerization." The decomposition of n-propyl-copper(i) gives propene and propane, but no six-carbon molecules. It therefore seems highly unlikely that propyl radicals are intermediates. Perhaps, as in the earlier but very similar report on the absence of eight-carbon molecules from the decomposition of triphenylphosphine-n-butylcopper, the mechanism involves initially the separation of alkene,... 

Pimentel et al. (2010) studied the OH-radical-initiated oxidation of isopropyl formate in the presence of NOx and reported the following products (molar yields) acetic formic anhydride (43%), acetone (43%), and HCOOH (15-20%). From the observed formation of CH2O in the chlorine-atom-initiated oxidation of iso-propyl formate, Pimentel et al. (2010) deduced that the fate of 0CH2(CH3)CH0C(0)H alkoxy radicals is decomposition (rather than reaction with O2). The resulting alkyl radical (CH3)CH0C(0)H is converted into the alkoxy radical 0(CH3)CH0C(0)H which then decomposes via... 

Chilton and Gowenlock85,87 pyrolyzed (z -C3H7)2Hg with NO and N2 as a carrier gas in a flow system at 230-280°C. They found (CH3)2 CHN=0 and (CH3)2C=NOH as products,85 the latter arising from the isomerization of the former. Woodall and Gunning454 studied the sensitized [Hg 6(3.Pi) plus NO Ilj)] decomposition of propane and its deuterated analogs at room temperature. Both n-propyl and isopropyl radicals were produced and added to NO. The product isomers, i.e., the respective oximes, were the principal products. An unusual feature of this study was that the oximes were formed readily at room temperature. The authors suggested that the reactant radicals might have been hot, and this coupled with the heat of addition could have facilitated the isomerization. 

Thermal decomposition of butane involves the unimolecular decomposition of sec- and n-butyl radicals as chain carrier steps, but little quantitative information can be obtained from the work. The best estimation of the A factor for the thermal decomposition of butyl radical is based on the high-temperature photolysis of 2-methylbutanal and has the value, log A — 15.32.64 Corresponding values for w-propyl radicals2 were 15.3655 and 13.9.62 In view of the complexity of these experimental systems, these compare reasonably with the value of 14.35 in Table XX. 

---