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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: third333 on April 28, 2010, 10:25:54 PM

Title: Benzaldehyde turned into solid?
Post by: third333 on April 28, 2010, 10:25:54 PM

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?

Title: Re: Benzaldehyde turned into solid?
Post by: hobobot on April 28, 2010, 10:34:40 PM

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

Title: Re: Benzaldehyde turned into solid?
Post by: Doc Oc on April 28, 2010, 11:51:44 PM

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

Title: Re: Benzaldehyde turned into solid?
Post by: orgopete on April 29, 2010, 12:56:36 AM

Aldehydes are easily oxidized. It is benzoic acid.

Title: Re: Benzaldehyde turned into solid?
Post by: nj_bartel on April 29, 2010, 04:01:39 AM

^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!

Title: Re: Benzaldehyde turned into solid?
Post by: pacifyer on May 12, 2010, 07:04:16 PM

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