benzaldehyde/nitroethane/methylamine condensation

[Vaaguh]

To a RBF containing 50 mmol benzaldehyde, 60 mmol nitroethane and 25 ml IPA there was added 5 mmol methylamine as an isopropanolic solution due to the fact that it was late the reaction was stirred overnight at 45 deg celcius. 8 hours later when the contents where being checked the solution was bright yellow with a noticeable benzaldehyde odor, is it posssible that perhaps not enough methylamine was added to the mixture so that nitropropene formation could not come to completion?

And would it be possible to let the solution cool down to RT, add a little bit of extra methylamine and stir the solution for say 4 more hours or would this hurt the entire mixture?

[GC_MS]

- prolong reaction time
- benzaldehyde is very fragrant

[Vaaguh]

The addition of some extra isopropanloic methylamine definately has not hurt the reaction mixture, another 8 mmol methylamine was added to this mixture and the whole was stirred for another 4 hours at 50°C from there it was put in the fridge for 30 minutes and beautiful long yellow needles  formed.




To who it might interest some TLC's where made and at the end of that 4th hour point there was only one spot detected with an Rf value of 0,61 using ethyl acetate as an eluent on silica gel 60 plates, benzaldehyde had a Rf of 0,5 under the same conditions.

[armageddon]

Congrats. I hope you weighed your crystals and can tell us the yield you got?

Greetz A

[Vaaguh]

The first crop weighed that came off weighed 3,9 g but after putting the mother liquor back in the fridge with a seed crystal a lot more crystals where recovered, this was repeated once more and in the end after recrystalisation from IPA and drying there was a total of 5,86 g (72%) phenyl-2-nitropropene as light yellow long needles with a m.p. of 63-64 °C

[armageddon]

In case you don't belong to the bees loving to use methylamine where they can (or better said if you have to make your own and want to save it) - I would suggest to use ethylenediamine diacetate as base/catalyst - yields are the same (about 70%), and purity of the end product is higher (mp 70°C)...

Downside: the condensation sometimes needs several days for completion. But if you're not in a hurry..

Greetz A