Reactions of phosgene with Group 12 halides

2 Reactions of phosgene with Group 13 halides 9.1.2.1 Reaction of phosgene with boron(in) fluoride 

The two earliest reports of the COClj-BFj system are apparently contradictory the earlier [738a] claims that phosgene and boron(III) fluoride interact to form compounds (but does not identify these in any way), the later [1329] suggests that phosgene and boron(III) fluoride do not form a complex, even at temperatures as low as -120 C. However, a more detailed investigation [1329] resolved these anomalies. The phase diagram for the COClj-BFj system is illustrated in Fig. 9.1, and shows clear evidence for complex formation at compositions BF3.COCIJ (m.pt. -134.3 C) and BF3.2COCIJ (m.pt. -137.0 C) [1329]. 

Although there is an obvious structure for the 1 1 adduct, proposing a structure for BF3.2COCIJ is more problematic the possibility of halide exchange occurring does not appear to have been considered. 

Phosgene and boron(III) chloride are miscible in all proportions [1329], as predicted earlier [738a] and the phase diagram for the COClj-BClj system (Fig. 9.3) reveals a eutectic point at -142.3 C (74.4 mole % COCIj) and no evidence for any complex formation. Moreover, the vapour pressure - composition isotherm (0 C) for this system (Fig. 9.4) shows a positive deviation from Raoult s law (although Henry s law appears to be well obeyed [649]), indicating the presence of unfavourable interactions between phosgene and boron(III) chloride [376]. Thus, the purification of boron(HI) chloride from traces of phosgene will not be complicated by the formation of a thermodynamically stable complex. 

A vapour pressure composition diagram (0 C) for the COClj-BClj system [376]. 

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