[wonka_vision]

Hello,
I'm working with oleic acid solutions (oleic acid and trifluoroacetate) at high temperatures (~320C), and I've noticed that the solutions tend to turn a dark brown. I've read up on this some, and it seems as though oleic acid will oxidize when exposed to air (esp. at higher temperatures). Does anyone have any experience with handling/working with oleic acid? Would simply keeping my solutions under argon help?

Thanks!

[asa029]

I don't have experience with oleic acid, but I have experience with keeping air out of my solutions/reactions. Proper Schlenck-conditions should keep the atmosphere inert (and remove the air). Just remember to purge first.

[BobfromNC]

Hello,
I'm working with oleic acid solutions (oleic acid and trifluoroacetate) at high temperatures (~320C), and I've noticed that the solutions tend to turn a dark brown. I've read up on this some, and it seems as though oleic acid will oxidize when exposed to air (esp. at higher temperatures). Does anyone have any experience with handling/working with oleic acid? Would simply keeping my solutions under argon help?

The double bond is oxidizing from oxygen/ozone in the air.   This is like olive oil going rancid or butter souring.   You need to keep them under argon when heating or they will oxidize.   The main products are the epoxides, which will open to alcohols and diols.  They will not act as oleic acids once oxidized, but more like long chain alcohols.  This is a similar problem with biodiesel production, as most seed oil based biodiesel is full of unsaturated (double bond containing) chains, which will oxidize in air to form varnishes and goos (those things that used to clog carburetors when they were still used...) which are also bad on fuel filters and fuel injectors.   

Bob

[the.khemist.ds]

Oleic acid will oxidise in the presence of air, and this is definitely speeded up by heating. Commonly I would expect the formation of hydroperoxides, peroxides, ethers, ketones and alcohols as initial species with, formation of oligomers and also degradation to produce smaller organic compounds. These processes are also catalysed by redox-active metals at room temperature.

To look at it another way - oleic acid isn't really a special case - many organic compounds would decompose in air at the sorts of temperatures that you are using: fundamentally you are burning the compound. It is just that you haven't quite got enough energy in the system to start a self-sustaining oxidation (fire).

I'm not sure exactly what you are trying to achieve by heating oleic acid with trifluoroacetate but performing the reaction in the absence of oxygen will definitely have an effect. For most processes, using a nitrogen atmosphere should be sufficient for this task.

[Wald_ron]

Nitrogen is a cheaper alternative to argon.

[asa029]

Nitrogen is a cheaper alternative to argon.

But in many cases not good enough for the inert conditions a given reaction demand.