From: Paul Harrison <pharriso**At_Symbol_Here**UNIVMAIL.CIS.MCMASTER.CA>
Subject: Re: [DCHAS-L] Benzaldehyde
Date: Tue, 18 Feb 2014 23:02:36 -0500
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: web-497082792**At_Symbol_Here**
In-Reply-To <731700108A7439498BE12EC6F8A2585ADC4052CA**At_Symbol_Here**>

It is most likely benzoic acid or perbenzoic acid. Oxidation of benzaldehydes that have been freshly distilled and hence are free of inhibitors is extremely fast. I have seen crystals at the end of a 3-hour undergrad. lab in a bottle that was fresh at the beginning.

If it forms a peroxide, then this would almost certainly not occur at the aromatic ring, but by removal of H radical from the aldehyde. This yields PhC=O radical and HOO radical, which would re-combine to form the peracid. PhC=O also likely undergoes loss of carbon monoxide, giving Ph radical that would end up as phenyl peroxide. The peroxy compounds would likely also photo-dissociate into carboxy radicals and alkoxy radicals, and so on. I would also speculate that one molecule of per-acid oxidizes another of aldehyde, thereby giving two benzoic acids. So overall it is unlikely that much peracid would build up.

The other key safety point is that aryl per-acids such as per-benzoic acid or meta-chloro derivative, mCPBA, are much more stable than alkyl peroxides such as those from ether. They likely can be handled by cautious addition of a reducing agent. Try iodide, and watch the iodine form!

If the bottle is large, however, or if you are not a chemist by training, I would urge more caution.


On Tue, 18 Feb 2014 23:59:19 +0000
Wayne Phan wrote:
> I just did a lab safety inspection and found a bottle of Benzaldehyde with crystal formation. The bottle is dated back to 5-25-1989. I am not sure if this is peroxide or just polymer being formed. What are your thoughts? If it is peroxide, what is the proper protocol for handling it?
> Thanks,
> Wayne

Paul Harrison
Associate Professor of Chemistry
Department of Chemistry and Chemical Biology
McMaster University
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