Electrophiles insertion

The kinetics and mechanism of iV-nitration reactions have been reviewed and the nitration of alkanes with nitronium hexafluorophosphate in CH2CI2 or EtN02 has been shown to involve direct electrophilic insertion of NO2+ into C-H and C-C a-bonds. ... 

In contrast to the radical processes described before, high selectivity is characteristic of electrophilic oxidation of methane.61 It reacts, for instance, with H2O2 in superacidic media to give methanol.1,62 The reaction is best explained by electrophilic insertion of the hydrogen peroxonium ion (H3Oj) into the methane C—H bond ... 

For the activation of methane, SO4 /Zr02 was found to be active for the reaction of methane with ethylene to form C3, t-C4, 1-C5 [64] In Table 5, the product distribution is compared with that of the other solid superacid, TaFs/AEC [65] For the chlorination of methane, the selectivity of S04 /Zr02 for the formation of methyl chloride exceeds 90% with 30% of chlorine conversion at 473 K and is above 80% with 70-90% conversion at 439 K The selectivity is enhanced by adding Pt, while Fe203-Mn02-S04 /Zr02 exhibits excellent sclectivities (99-100%) at lower conversions [66] The electrophilic insertion is said to involve electron-deficient metal-coordinated chlorine at the methane C H bond... 

Chloromethane is an important industrial chemical. Olah et al. [56] have reported the selective catalytic monochlorination of methane to chloromethane over superacidic sulfated zirconia solid catalysts, for example 804 /Zr02, Pt/ S04 7Zr02, and Fe/Mn/S04 7Zr02- The reactions were conducted in a continuous-flow reactor under atmospheric pressure. At 200 °C with 30 % chlorine the selectivity to chloromethane was > 90 %.The selectivity could be enhanced by adding platinum. The only by-product was CH2CI2. The latter is formed by the subsequent chlorination of chloromethane. No chloroform or carbon tetrachloride was formed. The authors postulated that chlorination occurs by an electrophilic insertion of an electron-deficient, metal coordinated, chlorine molecule into the C-H bond of methane. One drawback of the process was that above 225 °C, part of the metal was removed as the metal chloride [56]. Formation and subsequent loss of volatile metal chlorides is a major pitfall that should be avoided during vapor-phase chlorination over solid catalysts. 

SCHEME 2.15 Stepwise mechanism of electrophilic insertion of SO3 into allylic C-F bond of hexafluoropropene. 

Enthalpies of activation are 7-lOkcalmor and the negative entropies (-30 to -40 cal cal ) are consistent with the associative kinetics. The linear relationship between log k and either the pK of RCO2H or Hammett cr constants for XC6H4CO2H suggest that the mechanism involves heterolytic 0—0 cleavage and electrophilic insertion of oxygen into the Pd—C bond, in what is proposed to be a concerted process/ ... 

Mechanistically, both reactions are electrophilic insertion reactions into the methane C—H bonds. In the platinum insertion reaction subsequent chlorolysis of the surface... 

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