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DraconicAcid
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[*] posted on 14-11-2019 at 18:26
Removal of aldehyde from alcohol

I made some cinnamyl alcohol recently, and wanted to get rid of any excess cinnamaldehyde. Recrystallization is tricky because of its low, low melting point (I managed to get it to crystallize from toluene/heptane in an ace bath, but then the crystals melted at RT and gave two layers- cinnamyl alcohol and heptane).

So I'm planning to get rid of excess cinnamaldehyde by making the sulphite addition product. Should I a) dissolve the crude alcohol in toluene, and wash several times with sulphite solution, or b) dissolve the crude alcohol in methanol, add sulphite, filter out the adduct, then re-isolate the alcohol?

Most of the references I can find are for purifying the desired aldehyde, rather than removing it as an unwanted impurity.

(The alcohol smells nice, though- most of the people I've shown it to detect a floral or rosy odour, with hints of cinnamon, although one person insisted it smelled like hot dog water.)



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DraconicAcid
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[*] posted on 14-11-2019 at 18:37


Never mind- found a reference. Wash organic layer with sulphite solution.

http://web.fscj.edu/milczanowski/eleven/cinnamin.pdf



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[*] posted on 20-11-2019 at 09:40


Yes - remove alcohol by distillation, mix with sat. aq. bisulfite soln. (adduct will form), filter, wash with DCM or chloroform, evap. solvent, hydrolyze with dilute HCl, extract, dry solvent, filter, evap. solvent, vacuum distill
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[*] posted on 20-11-2019 at 10:39


Alternately, just run it through a short chromatography column. Cinnamaldehyde should elute much faster than cinnamyl alcohol. It would be a trivial separation.



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[*] posted on 20-11-2019 at 10:58


There is some interesting information in this old paper....

Hill, A. J., & Nason, E. H. (1924).
The Utilization Of Cassia Oil For The Synthesis Of Cinnamyl Alcohol.
Journal of the American Chemical Society, 46(10), 2236–2246.
https://sci-hub.se/10.1021/ja01675a014


/CJ



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DraconicAcid
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[*] posted on 21-11-2019 at 17:28


Quote: Originally posted by nimgoldman  
Yes - remove alcohol by distillation, mix with sat. aq. bisulfite soln. (adduct will form), filter, wash with DCM or chloroform, evap. solvent, hydrolyze with dilute HCl, extract, dry solvent, filter, evap. solvent, vacuum distill


I'm not trying to save the aldehyde, just get rid of it from the alcohol I'm trying to purify. Distillation isn't an option because the bp is too high (and I don't have a pump for vacuum distillation).

Recrystallization seems to improve it a bit, but it still melts after the collected solid returns to room temp (even after washing with sodium bisulphite). I'll have to run a column.



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S.C. Wack
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[*] posted on 21-11-2019 at 18:50


Did you dry before evaporating? Maybe it's just a little wet.



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[*] posted on 21-11-2019 at 20:51


Quote: Originally posted by S.C. Wack  
Did you dry before evaporating? Maybe it's just a little wet.


Yes, over anhydrous sodium sulphate, twice (dissolved in toluene, which has a low affinity for water anyway).



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