Mellitates, metal, decompositions

Pyrolyses of formates, oxalates and mellitates yield CO and C02 (H2, H20 etc.) as the predominant volatile products and metal or oxide as residue. It is sometimes possible to predict the initial compositions from thermodynamic considerations [94], though secondary reactions, perhaps catalyzed by the solids present, may result in a final product mixture that is very different. The complex mixtures of products (hydrocarbons, aldehydes, ketones, acids and acid anhydrides) given [1109] by reactants containing larger organic groupings makes the collection of meaningful kinetic data more difficult, and this is one reason why there are relatively few rate studies available for the decompositions of these substances. 

The decompositions of selected transition metal squarates (MC4O4) were identified as being of interest because they contain a fiirther organic anion that, like the oxalates and mellitates, contains no hydrogen, so decreasing the complexity of product mixtures and secondary reactions. 

Correlation between selected values of E, for decompositions of oxalates and mellitates with the enthalpies of oxide formation [108] (some mean values of E, are included). The magnitudes of E, thus appear to be controlled by the strengths of the M-0 bonds. Two trends may be discerned. Reactions where breakdown of the oxalate anion are believed to be catalytically promoted by the metal product, have slightly lower E, values ( ), compared to reactions in which the residual product does not promote decomposition, including the mellitates where carbon deposition inhibits catalysis (+). 

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