Monitoring the pH-Dependent Oximation of Methyl Ethyl Ketone and Benzaldehyde by in situ Fourier Transform IR Spectroscopy in a Heterogeneous Liquid–Liquid Two-Phase System

In situ Fourier transform IR spectroscopy was a useful tool in monitoring the pH-dependent and two-step oximation of methyl ethyl ketone and benzaldehyde in a liquid–liquid two-phase system, one phase of which was water. Carrying out the oximations at pH 8, the oximation was complete within 45 min and the corresponding carbonyl compound–hydroxylamine adduct (2) could be detected as an intermediate, but at pH 10, the corresponding oxime (3) was formed faster, practically without the appearance of the intermediate. At pH ∼ 2.5 using methyl ethyl ketone, the protonated form of the corresponding oxime (3'a) developed gradually without the transient appearance of the intermediate (2). pH dependence of the 3a → 3'a and 3'a → 3a interconversions were studied in separate experiments.