GLYOXIME AND OTHER DIOXIMES

We start with butane-2,3-dione dioxime, more commonly known as dimethylglyoxime (dmg). It is a classic reagent for the analysis of NP, the green aqueous solution of metal ions transforming into a vibrantly red precipitate of Ni(dmg)2 complex it is one of the stars of the show in Ponikvar and Liebman s analytical chemistry chapter in the current volume. Here the stereochemistry is well-established and well-known—both OH groups are found on the same side as their adjacent CH3 group on the butanedione backbone. There have been several measurements of the enthalpy of formation of this species for which we take the one associated with this inorganic analytical chemistry application, i.e. with diverse metal complexes and chelates . 

First of all, we may compare the values for this species and its lesser-methylated derivatives, the parent ethanedial and 1,2-propanedione dioximes, respectively. The former are only for the solid state. The differences for sequential methylation are the all but indistinguishable 36.2 and 36.1 kJmol and so we feel confident in this set of numbers. We also find that, at least for unstrained species, the gas phase olefin and aldehyde reactions in equations 29 and 30 are roughly endothermic by ca 4 kJmol .  

From the enthalpies of formation of gaseous acetaldoxime and butanedione dioxime we find the corresponding reaction 31 (R = Me) is exothermic by 20 kJmoH.  

We have no prior experience with diitnines to make any disparaging or supportive comparison but the result is implausible. Since we earlier accepted the enthalpy of formation of acetaldoxime, it is the dioxime that is seemingly suspect. From an expected enthalpy of reaction 32 of ca 4kJmol , the enthalpy of formation of dmg is calculated as —41 kJmor. Not only is this derived value very different from the one presented in Table 3, it is wildly divergent from the one that appears in Reference 1 and which is not in Table 3 —80.8 kJmol .  

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