DaniloTraverg
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Cinnamaldehyde failed to condense?
I've been trying to make cinnamaldehyde and derivatives for a while now, all have failed for some reason. The general reaction is the claisen-schmidt,
Benzaldehyde is mixed with isopropanol and NaOH, and acetal/propional is dripped with stirring over 5 hours. The solution turns yellow, and a yellow
liquid is isolated, but the issue is that the isn't any cinnamon smell, just benzaldeyhde. Everywhere I've found examples of people claiming the
cinnamon smell is easily noticeable and very apparent. These have been the experiments:
1.
5 g benzaldehyde, 5 g isopropanol, 0.5g NaOH (chips) are mixed for a while until the NaOH partially dissolves. I couldn't fully dissolve it for some
reason. while adding aldehyde and stirring the solution turned into a gel and more isopropanol was added a couple of times to allow stirring to
continue. Yellow product, benzaldehyde smell without ANY hint of cinnamon.
2. - solventless
same as 1 but without any isopropanol, the NaOH was turned to powder first. Even before dripping aldehyde into the mix the benzaldehyde and NaOH
turned into a sort of gel, the hydroxide clumping into chunks again too. Mixed by hand to break up gel, dripped aldehyde but again no cinnamon product
formed.
3. - with water
Same as 1 but added 50% isopropanol/water. The NaOH dissolved fully this time, there seemed to be less gel, but again, no product.
I'm unsure how to continue, this seems so simple and I keep messing it up.
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DraconicAcid
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Wouldn't benzaldehyde with strong base give the Cannizaro reaction? Benzyl alcohol and sodium benzoate?
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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DaniloTraverg
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I understand that could happen theoretically, but I followed other forum posts, patents, and the theory regarding the claisen-schmidt. The cannizzaro
isn't mentioned anywhere a side reaction. Though I wouldn't exclude it as an option I don't understand why nobody's experienced this issue.
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DraconicAcid
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I don't know. I've done the malonic acid condensation to give cinnamic acids several times, but never the aldehyde.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Pumukli
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I think Cannizaro is a slow reaction at room temperature.
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Lionel Spanner
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Forming cinnamaldehyde using Claisen-Schmidt requires acetaldehyde (an enolisable carbonyl) as well as benzaldehyde (a non-enolisable carbonyl.) It's
not being formed here because the benzaldehyde has nothing to react with.
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DaniloTraverg
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Quote: Originally posted by Lionel Spanner  | | Forming cinnamaldehyde using Claisen-Schmidt requires acetaldehyde (an enolisable carbonyl) as well as benzaldehyde (a non-enolisable carbonyl.) It's
not being formed here because the benzaldehyde has nothing to react with. |
"Benzaldehyde is mixed with isopropanol and NaOH, and acetal/propional is dripped with stirring over 5 hours"
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bnull
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It seems you are using too much NaOH. Try less hydroxide or 2 to 4 times the amount of benzaldehyde.
Are you following a published procedure?
Did you apply heat in any of the runs?
It looks that either a Cannizzaro or an aldol reaction is going on. Or maybe both, who knows.
Edit: One more thing. It seems you can use sodium carbonate to avoid Cannizzaro.
[Edited on 7-11-2024 by bnull]
Quod scripsi, scripsi.
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DaniloTraverg
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| Quote: Originally posted by bnull | It seems you are using too much NaOH. Try less hydroxide or 2 to 4 times the amount of benzaldehyde.
Are you following a published procedure?
Did you apply heat in any of the runs?
It looks that either a Cannizzaro or an aldol reaction is going on. Or maybe both, who knows.
Edit: One more thing. It seems you can use sodium carbonate to avoid Cannizzaro.
[Edited on 7-11-2024 by bnull] |
I'm using patents (google alpha methyl cinnamaldehyde synthesis), youtube videos on the cinnamadehyde synthesis and a few vespiary posts.
No heat was applied. I might try less hydroxide or the carbonate.
Does the ratio of water to alcohol matter here? Is using water at all good?
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bnull
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| Quote: | | Does the ratio of water to alcohol matter here? Is using water at all good? |
There is a brief description of a procedure in the Kirk-Othmer Encyclopedia of Chemical Technology (2001), vol. 6, p. 175:
| Quote: | | The commercial process is carried out in the presence of a dilute sodium hydroxide solution (ca. 0.5-2.0%) with at least two equivalents of
benzaldehyde and slow addition of the acetaldehyde over the reaction period (US patent 2,529,186). In this manner, self-condensation of acetaldehyde is minimized and yields in the range of 77-85% are obtained. However, even with
these precautions a detectable amount of 5-phenyl-2,4-pentadienal (CAS#13466-40-5) is invariably formed. |
Apparently water is not an issue. Try using only water, no other solvent.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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