A Brief Discussion of Aliphatic Oximes in Aqueous Solution

A Brief Discussion of Aliphatic Oximes in Aqueous Solution 

Despite a literature that begins early in the 20 centuiy , we only briefly discuss the energetics of the aqueous phase synthesis of oximes and bypass the intermediacy of a,Af-dihydroxylamines (hydroxycarbinolamines) and any zwitterionic or charged species. With great simplification we would thus write equation 26  

There are three environments that we may consider for this reaction iyw-acetaldehyde oxime data in the condensed phase , the gas phase and in aqueous solution . The reaction exothermicities are 51.0, 56.5 and ca 53 kJmoD, respectively. The only other case where the values are known for all three phases is that of acetone, equation 28  

In this case, the enthalpies of reaction are 52.1, 45.7 and 44.6kJmoD where the enthalpies of formation of solid and gaseous acetone oxime are from References 1 and 4, respectively, and the enthalpies of oximation in aqueous media are from References 49a and 49c. In both cases, the values are comfortably similar for the three phases. Perhaps we should not be too surprised that the values are close—after all, the number of hydrogen bonds are the same on the two sides of the reaction. However, nothing prepares us for the observation that the aqueous phase oximation enthalpy of propionaldehyde is 73.2 kJmoD, even though we recall problems with the enthalpy of formation of EtCH=NOH. 

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