1-(2,5-dimethoxyphenyl)-2-nitropropene was made with Henry condensation, using 2,5-DMBA, acetic acid, nitroethane and ammonium acetate.
Everything quite pure, except for the nitroethane. This one was made via ethyl bromide and sodium nitrite in DMF.
The nitroethane was not distilled, and there was still a bit of DCM that was used for the nitroethane extraction mixed in.
Lower BP impurities have been mostly removed from the nitroethane with aspirator vacuum, oil bath at maximum of 60 C or so.
Let the Henry run for 4 h, oil bath at 100-110 C.
Evaporated the AcOH with aspirator vacuum. Added water, extracted twice with DCM. Lower organic layer orange-brown, top watery layer light yellow
color.
Evaporated the DCM with aspirator vacuum. Dissolved the oily residue in 50 ml IPA, put in freezer, nothing seen for 40 min or so, then a few yellow
solids on bottom, in a few more minutes everything solid, nice yellow color.
Added a bit more IPA, stirred, vacuum filtered. Nice, bright yellow color on the nitropropene, filtrate redish color.
Tried to dry nitropropene in hot plate at low heat, then it started to melt. Covered with Saran Wrap and put back in freezer, again solid. It seems to
melt at RT.
I guess I have some 5 g, estimated, from 10 g of 2,5-DMBA.
I would like to know if I can make this to stay solid at RT, and also what might be causing it to melt, impurities or what else.
Thanks. kclo4 - 2-8-2009 at 13:39
Do you know what the melting point of the nitropropene mentioned is to begin with?
That might be important. xwinorb - 2-8-2009 at 14:21
The melting point is 73-75 C. From PIHKAL # 54.
A bit more information : After placing it back in the freezer, nicely solid. Weighted 8.2 g, which is a yield of aproximately 60 %, but the solid
nitropropene is still smelling of IPA. In a few minutes more, it started to melt again, this time for sure at RT, no hot plate heat used.
I would like to be able to dry it till the IPA smell is gone and to have a better idea of what the real yield is. Besides this, no problem having some
IPA mixed in, I am planning to reduce this to the mentioned # 54 anyway, and I plan to use acidic Al-Hg. A bit of IPA mixed in is not an issue.
Right now, I have vacuum packed the nitropropene ina small mason jar and keeping in the freezer.kclo4 - 2-8-2009 at 14:45
Perhaps gently heat it on a hot water bath while pulling a vacuum?
It seems like the IPA being present could appear to change its melting point, while dissolving it at RT. Heating it under a vac would evaporate all of
the IPA, H2O, etc and probably up its MP. xwinorb - 2-8-2009 at 15:44
After my last posting, it also occured to me that maybe the IPA ( and as kclo4 has posted ) maybe water could be making the xtals to melt at RT.
I think I have seen the IPA making some other substance ( also 2,5 substituted ) to melt a bit while drying on the hot plate, but not at RT. This one
is a PEA, not a nytrostyrene nor a nitropropene.
I think I will try to freeze it again to make it solid, then to move it to another container or BF and I wil try to dry it under vaccum as you have
suggested.
Thanks.Barium - 2-8-2009 at 19:55
xwinorb,
1. The process in which your benzaldehyde reacts with nitroethane to form the 1-phenyl-2-nitropropene is called the Knoevenagel condensation, not
Henry. The Henry reaction (also called the nitroaldol reaction) gives nitroalcohols (which can be dehydrated to nitroalkenes) from aldehydes and
nitroalkanes.
2. Your product is dirty. Clean it up and it crystallize perfectly fine.xwinorb - 2-8-2009 at 20:39
To Barium : Thanks for correcting me, I though it was the Henry condensation, I was wrong.
I just tried to recover more from the filtrate, I got a fraction of 1 gm, a bit more brownish color than the main fraction, but this one xtalized OK,
nice and dry.
I guess I will try to do the same to the main fraction later on. I would rather avoid to re-xtalizing it, I am afraid I might loose too much of the
nitropropene.Nicodem - 2-8-2009 at 23:10
I guess I will try to do the same to the main fraction later on. I would rather avoid to re-xtalizing it, I am afraid I might loose too much of the
nitropropene.
It's not like you are going save it by not recrystallizing it either! What do you think, that if your product contains a bunch of the starting
material, your yield is nevertheless 60%? You simply need to recrystallize it.
Next time follow the condensation with TLC and you will save yourself such troubles.Polverone - 3-8-2009 at 08:35
Troubleshooting a pihkal prep isn't really appropriate here.
