I just received 1liter of benzaldehyde in the mail, I want to switch the container it came in which is a soft plastic bottle to a more air tight glass
container. The bottle it came in isn't that air tight I'm guessing because I can smell the benzaldehyde when I sniff the bottle. Anyway I have a nice
glass bottle I would like to store it in but I'm trying to figure out the best way to transfer it. In the past it seems as tho I got a lot of
oxidation when transferring benzaldehyde and I would see some benzoic acid inside the bottle.
So my question is what is the best way to do this? I have some Co2 containers with a valve set up and a hose. Maybe I can use this some how and
possibly fill up a big plastic bag with the gas and try to use it as you would a glove box? Also would it be wise to fill the new glass container with
the co2 gas or displace the oxygen in the head space of the bottle with it after I transfer the benzaldehyde?
Thanks for the help in advance! clearly_not_atara - 21-4-2017 at 10:15
Doesn't benzaldehyde autooxidize to benzyl benzoate?
Anyway Wikipedia tells me that benzaldehyde freezes at a frigid -57 C. Assuming that the rate of oxidation increases with temperature (which seems
reasonable) it should suffice to put the benzaldehyde in the freezer and transfer it while it is very cold (-20 C or lower). You may want a small
spatula to ensure it all pours out. LD5050 - 21-4-2017 at 11:07
Doesn't benzaldehyde autooxidize to benzyl benzoate?
I'm not 100% sure but I believe it autooxidizes to benzoic acid, atleast that is what I frequently observe when I deal with this stuff. I will always
find white powdery benzoic acid around the threads of the bottles I keep it in or on the sides of the beakers after using them to measure a certain
amount or whatever.karlos³ - 21-4-2017 at 11:10
You have to distill it before each use, to get rid of the benzoic acid.Ozone - 21-4-2017 at 11:11
You get (primarily) benzoic acid. But, this is a slow process. Assuming the product is in a reasonable state of purity, just pour it into a clean
container, and purge the airspace with an inert gas. Seal tightly and store refrigerated.
There will always be some amount of benzoic acid in stored benzaldehyde. This is why (if it matters) it is frequently purified just prior to use. It
can be stabilized, but that would also necessitate purification. Benzoic acid is easy to remove.
O3LD5050 - 21-4-2017 at 13:12
Would Co2 work for a suitable inert gas?adk - 21-4-2017 at 20:11
No. CO2 is not an inert gas because of its ability to form carbonic acid in water upon dissolution. My guess is that it will vastly increase the rate
of oxidation.
Use Nitrogen or Argon.
Benzaldehyde should be distilled slowly under vacuum and then stored in an amber glass bottle with inert gas, away from light and heat. Argon is best
as it is moderately heavier than air and tends to stay in the bottle better than Nitrogen. If you can't vacuum distill it, filter whilst moving to the
new bottle. Purging the receiving bottle with gas is also good practice. Dr.Bob - 24-4-2017 at 06:28
Just use small glass bottles with tight lids, and fill each one nearly full, that will reduce any residual air. If you have N2 or argon, that would
be great, but if you simply leave only a little headspace, that will limit the oxidation. But as everyone said, their will always be traces of
benzoic acid in it, sometimes benzyl alcohol (from redox of 2 benzaldehyde to one benzoid acid and one benzoic acid, I think it can occur in some
cases), and likely traces of other stuff. But for many reactions, those impurities don't matter (eg, in most reductive aminations, traces of acid
don't hurt much), in other cases, you will need to distill it.
