[third333]

I am just curious if anyone knows why Benzaldehyde, if stored properly, would turn into a brown solid at the top of its container after a significant period of time? I guess for this to happen, storage must have been improper. Any ideas to why, or what the solid might be?

Could it have been exposed to air and water, and oxidized to Benzoic Acid?

[hobobot]

It's a very slow cannizzaro reaction. I think the solid is benzoic acid.

[Doc Oc]

Don't Cannizzaro's require hydroxide?  Otherwise I don't see how that can just disproportionate.

[orgopete]

Aldehydes are easily oxidized. It is benzoic acid.

[nj_bartel]

^Agreed.

Distilled some benzaldehyde 2 years ago, blew a little nitrogen in, stoppered the flask, then parafilmed the stopper and stuck it in the fridge.  Still crystal clear liquid today - so just store it properly!

[pacifyer]

As said above, aldehydes oxidize easily, even by action of air, to give benzoic acid.