Dissociation, Dismutation and Photochemistry of Phosgene

As seen in Chapter 6, phosgene is thermodynamicaliy stable under standard conditions with respect to its elements. Equation (8.1), and with respect to dissociation. Equation (8.2). 

however, thermodynamically unstable with respect to dismutation. Equation (8.3). Besson 

This chapter describes the dissociation and dismutation processes for phosgene in some detail, as well as examining its photochemlcally induced decomposition. 

The thermal dissociation of phosgene into carbon monoxide and elemental chlorine. Equation (8.2), is the reverse of the reaction used widely, either thermally, catalytically or photochemlcally promoted, for the synthesis of phosgene (see Section 5.1). Thus, much of the chemistry relevant to this Section has already been covered in Chapters 5 and 6. Much of the early work, both kinetic and thermodynamic, was marred by a lack of appreciation of the importance of high purity, and the fact that the system takes a very long time to come 

A modern study of this system by Lord and Pritchard [1275] confirmed that the data of Bodenstein and Plaut [218] were of the highest accuracy when the data from Bodenstein and Plaut [218] and the modern study [1275] are combined (see Fig. 8.2(B)), a value of AH of +(112.5 1.5) kJ mol is obtained for reaction (8.2) from the van t Hoff plot [1275]. However, as the slight curvature of the plot betrays, AH varies slightly with temperature. The best data treatment yields AHjgg as +(108.6 i 0.4) kJ mol [1275]. The equilibrium constants for Equation (8.2) are given by [1275]  

---