Kinetics and mechanisms of the imine exchange reactions of O-alkyl and O-aryl oximes with O-alkyl-and O-aryloxyamines, respectively, were studied by 1 H NMR spectroscopy in aqueous solutions. The reaction between benzaldehyde O-methyloxime and O-ethylhydroxylamine at 60°C is first order in both oxime and the alkoxylamine (the second-order rate constant k 2 = 0.86 AE 0.08 l mol À1 min À1 at pD 2.9), the reaction being subject to acidic catalysis. A similar imine transfer was studied in the reaction of 1,3-diaminooxypropane with bifunctional oximes. Testing of various additives as potential catalysts for the reaction revealed imidazole as a moderately effective catalyst. The exchange in O-aryl oximes was studied in the interaction between 3-pyridinealdehyde Ophenyloxime and O-(p-nitrophenyl)hydroxylamine. The reaction is first order in the oxime, but its rate is independent on the aryloxyamine concentration and pD. The proposed mechanism involves a rate-limiting hydration of the oxime molecule. Mechanisms of the exchange reactions are discussed in relation to their possible use to generate diverse pools of compounds for the recently proposed 'dynamic' combinatorial chemistry approach.

ABSTRACT:Values for the surface tension, p, of 85 mJ/m 2 and for the contact angle of wetting by water as its saturated vapour, q V , of 75º are proposed as criteria for distinguishing between hydrophilic and hydrophobic solid surfaces. It is shown that the water boundary layers at hydrophilic surfaces are more ordered while those at hydrophobic surfaces are less ordered relative to the situation in the bulk water structure. The localised model can be used to describe the state of motion of water molecules at a hydrophilic surface, while the motion of water molecules near a hydrophobic surface conforms to the non-localised model.

Since humidity has an important role in determining the rate of oxygen absorption kinetics by iron-based oxygen scavengers, using the models derived and presented in the present publication can bring upon a better understanding of the oxygen absorption process and a more efficient way of using oxygen scavengers in the packaging and storing of different oxygen sensitive foods.

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