Boffis
International Hazard
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Registered: 1-5-2011
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Recovering polymerised acetaldehyde
Some time ago I was given a very old, 100g, bottle of phenylacetaldehyde. It has partly converted into fluffy crystalline aggregates floating in a
semisolid, almost colourless, glassy resin. Warming softened the resin and then I discovered that a small amount, about half its volume, of 95%
ethanol rapidly liquifies the resin and at about 50 C becomes a mobil liquid that can be decanted from the crystalline material. The initial liquid
was a clear pale yellow with a strong smell of phenylacetaldehyde but after a few days became cloudy and now (after 2 weeks) has despoited copious
crystals.
The crystalline residue was dissolved in 30ml of boiling ethanol (95%) and cooled, allowed to evaporate to about 20ml and left to stand for several
days with occassional stirring. Eventually copious white crystals formed.
Filtering either liquid is going to be slow due to their viscosity.
Does anyone know much about phenylacetaldehyde and can the resin be de-polymerised? I wondered if, for instance, I could add a catalytic amount of
sulphuric acid and then steam distil it? Or could I evaporate the alcohol, dissolve in acetic acid (which also seems to dissolve it) and oxidised with
chromate/acetic acd/sulphuric acid mixture to get phenylacetic acid/benzoic acid?
Any thoughts?
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Fery
International Hazard
Posts: 1127
Registered: 27-8-2019
Location: Czechoslovakia
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I hope this helps:
https://patents.google.com/patent/US2649462A/en
they used thermal cracking of the trimer. But your sample may be longer chain polymer than trimer.
I wonder whether some O2 from air did not enter your sample, but it is easy to get rid of phenylacetic acid by washing with aqueous NaHCO3. I saw very
old bottle of benzaldehyde with large amount of crystals of benzoic acid (a cap had to be leaking).
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Boffis
International Hazard
Posts: 1927
Registered: 1-5-2011
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Hi Fery, Thankyou very much thats a real help! I filtered of the white crystals that I presumed were phenylacetic acid but once washed with more
alcohol and dried were odourless and insoluble in dilute alkali. I suspect that they are the Tribenzyl-trioxane the patent talks about. Interestingly
when I mixed the washing alcohol with the original filtrate it soon started to turn cloudy and by this morning the beaker was half full of white
precipitate again. I think the lower viscosity of the alkoholic solution promotes nucleation of the trimer.
I'll keep people posted.
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