2 research outputs found
NMR Spectroscopic Study of the Aldoxane Formation in Aqueous Acetaldehyde Solutions
Crotonaldehyde
is an interesting intermediate in the chemical industry.
It is usually produced from aqueous acetaldehyde in a two step process
in which the first step is carried out under basic and the second
step under acidic conditions. It is commonly assumed that acetaldehyde
is converted in the first step to acetaldol and that acetaldol is
subsequently dehydrated in the second step to crotonaldehyde. We demonstrate
by <sup>1</sup>H and <sup>13</sup>C NMR spectroscopic studies that
acetaldol is hardly present in the reacting solutions at lower temperatures
and that the key intermediate is aldoxane (2,6-dimethyl-1,3-dioxane-4-ol).
For the first time, data on the chemical equilibrium of the aldoxane
formation in aqueous acetaldehyde solutions is provided. Furthermore,
preliminary information on the kinetics of that reaction is presented
Online <sup>1</sup>H NMR Spectroscopic Study of the Reaction Kinetics in Mixtures of Acetaldehyde and Water Using a New Microreactor Probe Head
Mixtures
of acetaldehyde and water are reactive multicomponent systems because
polyÂ(oxymethylmethylene) glycols are formed. A study on the kinetics
of the formation of these oligomers was carried out using a new microreactor
NMR probe head that combines online flow <sup>1</sup>H NMR spectroscopy
with microreaction technology. The study covers temperatures between
278 and 298 K and pH values between 3.5 and 10.3. From the peak areas
in the <sup>1</sup>H NMR spectra, quantitative results for the conversion
of acetaldehyde were obtained. On the basis of the new data, a reaction
kinetic model was developed and numbers for the kinetic constants
of polyÂ(oxymethylmethylene) glycol formation were determined together
with a correlation that describes their dependence on the temperature
and pH value