A Study of the pH Dependence of the Two‐Step Oximation of Acetone by in situ Fourier Transform Infrared Spectroscopy

Abstract

In situ Fourier transform IR spectroscopy has been found to be an appropriate tool for the evaluation, monitoring and optimization of the pH dependent and two-step oximation of acetone in water. When carrying out the reaction at 5°C, the intermediate formation of the acetone-hydroxylamine adduct (2) was observed at pH 8.5, while at pH 10, the oxime (3) was formed almost instantly. Identification of the intermediate (2) was promoted by the IR spectrum obtained by B3LYP/6-31++G(d,p)//PCM calculations. At pH ∼ 2.5, the protonated form of the oxime (3') developed gradually, but the intermediate (2) could not be observed. The pH dependence of the stability of the intermediate (2) and the (3' → 3) and (3 → 3') interconversions were studied in separate experiments. An equilibrium was observed in the latter case.

Liquid–liquid synthesis of oximes from carbonyl compounds: formation under neutral conditions and degradation at acidic hydrometallurgical process conditions

“…Carbinolamine formation rate is known to be influenced by pH and the structural reactivity of the carbonyl and the amine compounds. 11‐12, 20, 22 The decomposition of the intermediate into the oxime occurs via acid or base catalyzed dehydration …”

“…The dehydration of carbinolamine proceeds rapidly both at low pH (≤2.5) and at high pH (≥ 10) but is slow under neutral and mildly alkaline conditions . For example, the formation of carbinolamine intermediate was reportedly observed in a homogeneous system during oximation of acetone at pH 8.5 but not at pH 2.5 or at pH 10 . Dehydration of the carbinolamine intermediate is considered the rate‐determining step under neutral and mildly basic reaction conditions .…”

Monitoring the Phosphorylation of Phenol Derivatives with Diethyl Chlorophosphate in Liquid–Liquid and Solid–Liquid Phase by In Situ Fourier Transform Infrared Spectroscopy, Part II

“…1 Hence, in situ FT IR spectroscopy may be an important tool in environmentally friendly ("green") chemistry. In addition, intermediates can be observed, 6,7 and equilibrium constants 8 can be determined by utilizing this up-to-date technique that is spreading in the chemical industry. Organophosphorus reactions may also be monitored by the in situ FT IR method.…”

A study on the Kabachnik–Fields reaction of benzaldehyde, propylamine, and diethyl phosphite by in situ Fourier transform IR spectroscopy

“…In situ Fourier transform infra‐red (FT‐IR) spectroscopy is a useful tool in environment friendly chemistry, as it allows optimization of the reaction conditions via monitoring the concentration profile of the components 1–5. The time‐dependent IR spectra also allow the establishment of formal kinetics or equilibrium constants 6,7 as well as detection of intermediates 8,9. In situ FT‐IR spectroscopy has been applied only rarely in organophosphorus chemistry 5,10,11.…”