|Oxidation by oxygen. Whenever you are in need of oxidizing a compound, oxygen must be the obvious choice. It is not, explosion risk plays a role. Not for the first time now a France-based research group takes up the challenge. They demonstrate here how it could be done with substrate 2-ethylhexanal (available through the oxo process) which requires oxidation to 2-ethylhexanoic acid (used industrially as precursor to certain catalysts). Key features: a continuous flow reactor, control of oxygen bubble flow and some free radicals as in free beer.|
The air droplets migrating in the continuous flow tube are big! See the movie in the supplementary info. Should resemble something like Taylor-Couette flow. The reaction does not require any catalyst which is odd for one described as a radical raction (autoxidation to the peracid, nucleoplic addition of a second aldehyde to a Criegee intermediate followed by rearrangement). The researchers went to some length to find an initiation mechanism and arrived at "a trace amount of over-oxidized aldehyde present at the ppm level in the starting materials"
Warning: the research group appears to be somewhat nomenclaturual (if that is a word) challenged: the supplementary info books 2-ethylhexanoic acid as 2-ethylhexylcarboxylic acid. Confusing.