Fluorination, direct thermochemistry

III. A NEW APPROACH TO DIRECT FLUORINATION A. Thermochemistry of Direct Fiuorination... 

Much of the discussion of oxygen flame calorimetry presented in section 7.3 is directly applicable to fluorine flame calorimetry. As in the case of bomb calorimetry, however, the special properties of fluorine combustion systems and problems associated with handling fluorine require a somewhat different experimental method [109,115,116]. Thus, for example, a metal burner should be used. Also, the fact that the mixing of many gases with F2 may lead to spontaneous ignition hinders the use of a premixed flame. Fluorine combustion calorimetry has been used to study the thermochemistry of important reactions, such as... 

Many current fluorine texts contain sections on the unfavorable thermochemistry of elemental fluorine reactions. A discussion of this thermochemistry, therefore, is helpful to establish the feasibility of direct fiuorination and gain insight into reaction conditions, to select, for example, the reaction temperatures that are most likely to lead to successful results. The tables of data presented and discussed deal with the thermochemistry of fiuorination of hydrocarbons. This choice was made because such data were most readily available. Similar arguments may certainly be made for inorganic compounds or polymers. 

In attempts to establish information about the relative heats of formation of various fluorinated methyl ions, studies (33,34, 38,39) have been carried out examining the directions of fluoride and hydride transfer reactions between fluoromethyl ions and various fluorinated methanes. Some studies (38,39) have also included ions and molecules containing chlorine atoms. Although the more quantitative aspects of this work will be covered in detail later in our discussion of the thermochemistry of fluorinated ions, it is interesting to examine here the relative Importances of competing reaction channels, shown in Table III. It should be pointed out that at sufficiently high pressures, stabilization of the dimethyl fluoronium Ion intermediates of the reactions is observed ( ). 

---