Carbonyl diiodide

Carbonyl diiodide has never been synthesized, and the only report of its observation is as a possibie (but improbable) component of the essential oil of a Hawaiian seaweed. The properties reported in this Chapter for carbonyl diiodide are therefore only estimated values, but they do give some insight into the reason for its non-existence. 

1 EVIDENCE FOR THE PRESENCE OF CARBONYL DRODIDE IN THE ESSENTIAL OIL OF Asparagopsis taxiformis 

In addition to the compounds mentioned above, the volatile oil of A. taxiformis (obtained by condensing onto a -78 C condenser finger in vacuo) contains iodine compounds. Separation of the oil using chromatography (on silica gel at 5 C) and analysis by g.c.-m.s. reveals a trace of material ( 0.1%) whose mass spectrum is not inconsistent with that expected for carbonyl diiodide (see Table 15.1) [310]. 

By analogy with the aerial decomposition of CHCI3 to COCIj, carbonyl diiodide has been postulated as an intermediate during thermal oxidation [310] or photooxidation [1627a] of triiodomethane  

Free iodine results from the further decomposition of the COI  

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Although CHI 3, and several other iodinated compounds, were readily identified by both n.m.r. and m.s. analysis of the crude oil obtained from A. taxiformis, many of the original iodine-containing compounds were found not to survive the chromatographic separation. Carbonyl diiodide was therefore postulated as an artefact that results from the decomposition of CHI 3 during the chromatographic process. Clearly, further work is required to substantiate or refute the possible formation of this compound, as this remains the only claim of its existence in the literature. 

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] ... 

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". ... 

The critical properties of carbonyl diiodide have also been estimated by Horvath [985], based on the Lydersen method ... 

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