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Author: Subject: Failed Henry reaction with 3,4,5-TMB
Planophore
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[*] posted on 10-7-2020 at 12:23
Failed Henry reaction with 3,4,5-TMB


I attempted a Henry reaction with 3,4,5-TMB using freebased phenethylamine as a catalyst, but after addition of plenty of water I didn't get any precipitate (500ml total addded)

Here was my procedure
12.5g 3,4,5-TMB (63.7mmol) was stirred in 130ml GAA. Then 0.77g phenethylamine (6.37mmol) was added dropwise to the reaction mixture with constant stirring along with 7.8g nitromethane (127.4mmol).

This mixture was then heated in a water bath maintained at 90 degrees Celsius for a bit over 1hr. During which the solution became gradually more yellow.

This was then slowly diluted with 250ml distilled water after which no change occurred. So the mixture was transferred to a larger flask and again 250ml distilled water was added to no avail.

Any recommendations? thanks
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njl
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[*] posted on 10-7-2020 at 15:54


Why do you have so much GAA?
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draculic acid69
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[*] posted on 10-7-2020 at 17:26


Try it with out gaa.
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karlos³
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[*] posted on 10-7-2020 at 18:04


Quote: Originally posted by draculic acid69  
Try it with out gaa.

No, some is needed at least, first its a good solvent for this reaction and second the acetate salt of the amine catalyst is much better working(with ethylamine acetate I got for the same substrate 94% and was able to reproduce that too using the same conditions).
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draculic acid69
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[*] posted on 10-7-2020 at 18:46


Ok it just seems like a bit too much gaa was used
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karlos³
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[*] posted on 10-7-2020 at 20:38


Thats for sure, this could have easily sufficed when used with tenfold as much of the other reagents!
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Planophore
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[*] posted on 10-7-2020 at 23:55


Thanks a lot.

I’m currently re-running the reaction on a smaller scale with significantly less AcOH and the colour is looking a lot closer to the characteristic yellow/orange of nitrostyrenes.

[Edited on 11-7-2020 by Planophore]
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Metacelsus
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[*] posted on 11-7-2020 at 06:00


Ammonium acetate is a perfectly good catalyst for this (giving 96% yields in my hands), there's no need to use phenylethylamine.



As below, so above.
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Planophore
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[*] posted on 11-7-2020 at 09:44


My re-run was very successful and everything looks good. I think the issue was - as you have all said - far too much GAA (I also slightly adjusted the quantity of amine). I appreciate your help

With regards to the ammonium acetate, I’ll give it a go if you’ve had such good yields with it. Do you mind telling me what molar equivalents you used?

I mostly used the PEA because I had PEA HCl on hand and the freebasing step is quite fun (and it’s quite water soluble, which is good for the workup)
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[*] posted on 11-7-2020 at 12:46


Here's the ammonium acetate procedure:

Aldehyde (25 mmol) and ammonium acetate (25 mmol, 1.93 g) were dissolved in nitromethane (6.8 mL, 7.7 g, 126 mmol) and acetic acid (15 mL). A few 3 Å molecular sieves were added and the mixture was refluxed with stirring for 1 hr. After cooling to rt and removing molecular sieves, the mixture was added to 13.8 g Na2CO3 suspended in 75 mL water. This mixture was extracted with ethyl acetate (2x20 mL). The combined extracts were dried (MgSO4) and evaporated to yield the adduct as yellow needles (24.5 mmol).




As below, so above.
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Planophore
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[*] posted on 12-7-2020 at 02:43


Appreciate it.

My yield of nitrostyrene with PEA was 74% (pre-recrystallisation), which is a bit disappointing
I’ll give it a go with ammonium acetate - was your 96% yield with TMB or another aldehyde?
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