Oximes protonated acetone oxime

These reactions are catalyzed by ammonium acetate, the function of which is to generate protonated imines (322). Under mild reaction conditions, condensation of a- hydroxyamino-oximes with acetone dialkylketals takes place. The procedure can be successfully applied in cases where direct condensation with acetone... 

The direct observation of this reaction is difficult because of the small equilibrium constant for imine formation. This type of reaction is therefore commonly studied by trapping the imine as it is formed with hydroxylamine, which reacts rapidly to form an oxime. Because the equilibrium constant for formation of the imine between methyl amine and acetone is so small, the equilibrium is established very rapidly. (The observed rate constant for a reaction proceeding to an equilibrium position is larger than the first-order rate constant for the forward reaction [7].) Thus the addition of methylamine and acetone to an aqueous solution results in the establishment of an equilibrium concentration of imine (and iminium ion) in several seconds. In several studies described below wherein reactions subsequent to imine formation occur, it is common to find a presumption of rapid imine equilibria prior to the slower o-proton abstraction or decarboxylation events that occur subsequently. 

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