ATTEMPTED SYNTHESES OF CARBONYL DIIODIDE

Similarly, the reactions between solid sodium iodide and either phosgene or carbonyl dibromide at -78 C produced only CO, Ij and NaX (X = Cl or Br) [1589b], and a reaction between tetrabutylammonium iodide and phosgene in dichloromethane at -78 C yielded only CO, Ij and [NBu ]Cl [1589b]. These results, particularly those obtained at low temperature, clearly point to COIj, even if it was formed as a transient intermediate, being extremely unstable. 

In a related reaction, the action of HI on ethanedioyl dichloride, (COC j, resulted in the formation of only CO and 13, rather than (001)3, even at -80 C. Carbonyl diiodide was presumed to be an intermediate in the decomposition process equation (15.2), itself being decomposed at low temperature [1937a]  

On the basis of the most recent and most complete data set [985], the thermodynamics of the dissociation reaction equation (15.3) strongly favour the right-hand side of the equation [1764]. The thermodynamic trends in dissociation of the carbonyl dihalide series of symmetrical compounds are shown in Table 15.3. 

These thermodynamic calculations would seem to rule out the possibility of preparing COIj by the simple combination of carbon monoxide and diiodine. However, if the oxidative decomposition of CHI 3 does proceed via the formation of COI3 as a primary product, then the kinetics of the dissociation of COIj becomes an important consideration in the question of the material s instability. 

Since authentic carbonyl diiodide has never been prepared, no data exist concerning the measurement of its physical properties. However, the boiling temperature of COIj has been estimated as 191 C by Horvath [985], based on the similarity principle (see Fig. 15.1), and taking into account its molecular mass of 281.82 g mol .  

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