DISMUTATION OF PHOSGENE

The dismutation reaction for phosgene is given in Equation (8.3), and is in competition with the dissociation reaction expressed by Equation (8.2). 

The dismutation reaction is potentialiy of some industrial significance. One of the general methods for the manufacture of tetrachloromethane is the chlorination of methane [2165]  

This reaction not only discards half of the chlorine, but generates four moles of waste hydrogen chloride for every mole of product. Moreover, the reaction is not 100% selective. Thus, a preferred method of industrial manufacture uses propene as a feed-stock  

The dismutation equilibrium of Equation (8.3) has been examined, by studying the reverse reaction between CCl and CO, between 628 and 718 K [1274a] a value of Mi of -(63 11) kj moP is obtained for reaction (8.3) from the van t Hoff plot (see Fig. 8.5) 

The thermodynamic parameters for Reaction (8.3) in the gas phase, as calculated from the JANAF Thermochemical Tables [359aa], are detailed in Table 8.2, and illustrated in 

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Some interesting relationships between Diphosgene , phosgene (Ref. 30) and the dismutation of phosgene into carbon tetrachloride and carbon dioxide (Ref. 31) are depicted in scheme 34 ... 

Fig. 8.8 The calculated effect of pressure and temperature upon the equilibrium yield of CCI4 from the dismutation of phosgene [ICI8,ICI9].

Although the catalytic dismutation of phosgene undoubtedly represents a valid and... 

The dismutation of phosgene and its related reaction with carbonyl difluoride are discussed in Section 8.2 and Chapter 13. Its reactions with CO(NCE)j (E = O or S) are... 

The overall reaction is, in effect, the catalysed dismutation of phosgene (see also Chapter 8) ... 

The first reaction is endothermic but rapid, whereas the second is exothermic but extremely slow. The presence of aluminium(III) chloride or iron(III) chloride catalyses this second step, and allows for the efficient dismutation of phosgene to proceed this catalysis has been discussed in terms of the following mechanism (M = A1 or Fe) [ICI6] ... 

Passage of the off-gases through a mass of bone-black, coke, or pumice results in the dismutation of the phosgene into tetrachloromethane and carbon dioxide (see Section 8.2). 

Molybdenum(V) chloride and, especially, tungsten(VI) chloride have been extensively studied as dismutation catalysts for phosgene (c/. Chapter 8). The first proposed mechanism for this catalysis involves the self-ionization of phosgene [775] ... 

Although the reverse of the dismutation reaction (see Section 5.4) was first observed experimentally in 1868 [1824a], when it was observed that phosgene was produced when carbon dioxide and tetrachloromethane vapour were passed over pumice heated to 350-400 "C, the forward reaction has proved more elusive (despite the overwhelmingly favourable thermodynamics). The potential value of the phosgene dismutation was recognised as early as... 

Fig. 8.6 The calculated [1825a] effect of temperature upon log, u(Xp) for the phosgene dismutation reaction, based on data from [3S9aa].

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