Alkyl-mercury bond dissociation

The available kinetic and thermochemical data are summarized in Table 7. Based on the approximate equality of E and D1+D2 and on the magnitude of the frequency factor, Billinge and Gowenlock98 would place dimethyl mercury, di-B-propyl mercury, di-isopropyl mercury (above 230 °C) and (on the basis of the frequency factor only, since thermochemical data are not available) di-n-butyl mercury in class II (simultaneous rupture into mercury and two alkyl radicals). If the high frequency factors are simply due to a general softening of the vibrations in the activated state, then in the case of di-isopropyl mercury D2 — 0, while for dimethyl and di-B-propyl mercury D2 is small but finite (2-3 kcal.mole ). However, within the limits of experimental error all of these alkyls for which thermochemical data are available may have E = Dl+D2, and thus all may belong to class II. At the same time it must be noted that some metal alkyls which are 

The hydrocarbon products of this pyrolysis were not determined but the mechanism is probably very simple, viz. 

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The mean bond dissociation energies (E ) given in Table 12 are based on thermochemical data at 25 C19. Unless previously discussed, the heat of formation of the metal alkyl used is that given by Long60. The higher values of E and D2 for dimethyl mercury are obtained when Long s recommended value for the heat... 

The homolytic thermal dissociation of R—M, previously used by Paneth in generating and studying free alkyl radicals, occurs with the more electronegative alkyls, such as those of mercury, lead, and the metalloids. Currently there is much interest in evaluating carbon-metal bond dissociation energies from such pyrolyscs (Section III.B). 

The most extensive studies on the dissociation energies of metal-carbon bonds have been made on organomercury compounds, in particular on the dialkyls of mercury. The mean bond dissociation energies, Zl(Hg—R), are of the order 20-30 kcal/mole, implying that Hg—C is normally rather a weak bond, and that mercury alkyls should decompose easily on heating. Although this is the case, it has transpired that Hg—C bonds are more... 

To perform the dissociation of the hydrocarbon to alkyl radicals with C—C bond scission, a hydrocarbon molecule should absorb light with the wavelength 270-370 nm. However, alkanes do not absorb light with such wavelength. Therefore, photosensitizers are used for free radical initiation in hydrocarbons. Mercury vapor has been used as a sensitizer for the generation of free radicals in the oxidized hydrocarbon [206-212], Nalbandyan [212-214] was the first to study the photooxidation of methane, ethane, and propane using Hg vapor as photosensitizer. Hydroperoxide was isolated as the product of propane oxidation at room temperature. The quantum yield of hydroperoxide was found to be >2, that is, oxidation occurs with short chains. The following scheme of propane photoxidation was proposed [117] ... 

Again several alkyls add—molybdenum, chromium, iron, cobalt, nickel, the alkali metal alkyls and aluminum alkyls react. A tin alkoxide has recently been studied by Russian workers and found to add to acetylenes. Mercury chloride, of course, adds and two cobalt—cobalt bonded compounds add to acetylene. The second is questionable because it dissociates in solution and the reaction may be a radical reaction, one cobalt adding to each end of the triple bond. 

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