Preparation of 1-(2,5-dimethoxyphenyl)-2-nitropropene
To a 250ml rbf is added 2,5-dimethoxybenzaldehyde (20g, 120mmol) and glacial acetic acid (100ml). To this is added nitroethane (13.6g, 181mmol) followed by ammonium acetate (8g). A stoppered vigreux condenser is attached and the mixture is heated on a steam bath for 3 hrs during which time the solution progresses from a clear yellow to a traffic light clear red. Most of the reagent/solvent was distilled off under vacuum, dark red oil being left in the flask. This was poured into water (~600ml) and extracted with one portion of chloroform (200ml). The chloroform was orange and the water yellow. The chloroform fraction was distilled off and this was used to re-extract the water. The yellow chloroform was then added to the flask and distilled off again. The distilled chloroform was a translucent white colour. The process was repeated again since the chloroform was still yellow in colour. It is remembered that at the start of the reaction the mixture was yellow and it is thought that un-reacted aldehyde is responsible for this coloration. A third re-extraction is done with diminishing yellow color still persisting. At this point it is wondered whether this process should be repeated indefinitely until the yellow colour vanishes or not to bother with it. Comments are appreciated but they must be given in the knowledge that they will be incorporated into the write-up and this post momentarily edited.
TLC plates are NOT on hand as unfortunately this is not a research laboratory. The yield did go up signifacantly though. Somewhere in the region of 15.5g WET crystals were collected. Crystalisation was brought about by boiling the solution in ~100ml methanol followed by freezing. The crystals being golden yellow in colour. These were then boiled in a generous ~120ml IPA. The amber syrup being left to recrystalise undisturbed at RT.
SWIM wonders why the procedure he is reading does not freeze the solution after refluxing in double the amount of nitroethane and ammonium acetate for twice the time, filtering the ice cold crystals. Two recrystalisations could then be brought about from MeOH & ETOH respectively.
RMM 2,5-dimethoxybenzaldehyde = (12.01 x 9) + (1.01 x 10) + (16.00 x 3)
= 166.91
20 / 166.91 = 120 mmol
RMM nitroethane = (12.01 x 2) + (1.01 x 5) + 14.01 + (16.00 x 2) = 75.08
13.6 / 75.08 = 181 mmol
RMM 1-(2,5-dimethoxyphenyl)-2-nitropropene = (12.01 x
+ (1.01 x 13) + 14.01 + (16 x 4)
= 187.22
Theoretical yield = 0.120 x 187.22 = 22.43g
