Trihalomethyl radicals

The preference for formation of dihalocarbenes (but not the trihalomethyl radicals) upon thermolysis of trihalomethyl mercury, silicon and germanium derivatives seems to be a result of intermolecular coordination, of type [1], and of a thermodynamic preference for the carbene-forming pathway. The... 

Choi W, MR Hoffman (1997) Novel photocatalytic mechanisms for CHClj, CHBrj, and CCljCO degradation and fate of photogenerated trihalomethyl radicals on TiOj. Environ Sci Technol 31 89-95. 

An unusual radical halogenation of hydrocarbons by phase-transfer catalysis may be performed by reacting alkanes with tetrahalomethanes. The reaction is initiated by single-electron oxidation of OH- by CHlg4. The tetrahalomethane radical anion formed decomposes to the 12 trihalomethyl radical [Eq. (10.56)], which is then involved in C—H activation and propagation steps 286... 

We have seen that the overall rates of addition appear to show evidence of steric effects and we have now found that the trihalomethyl radicals also show some evidence of a steric effect. Table 12 compares the relative rate and orientation of the addition to olefins of perfluoroalkyl radicals. There is a dramatic difference between Tables 10 and 11 on the one hand, where the main feature is the similarity of the rates and orientation ratios, and Table 12. In... 

The oxidation scheme for halomethanes not containing a hydrogen atom is similar to that for those which do, except that it is not initiated by tropospheric reaction with hydroxyl radicals, since the fully halogenated methanes are unreactive. Consequently, substantial amounts of CFCs and halons are transported intact up into the stratosphere, where they absorb UV radiation of short wavelength and undergo photodissociation (equation 36) to a halogen atom and a trihalomethyl radical. The halogen atom Y may enter into catalytic cycles for ozone destruction, as discussed in the introduction. 

Carbon tetrahalides are good electron acceptors and react with electrons to give trihalomethyl radicals and halide ions. Amines are known to react with carbon tetrahalides by an electron-transfer mechanism (Wyrzykowska et al., 1978 Iwasaki et al., 1978). Some careful product studies have been made of the reaction between carbazole and carbon tetrachloride (Zelent and Durocher, 1981). 

Likewise, several tetrahalomethanes add a trihalomethyl group and a halogen to the carbons of the double bond of an alkene under radical conditions. Examples are provided in the following equations ... 

---