u/EdwardTriesToScience

The procedure is based off of Daniel Traschel's:

a mass of aldehyde (4-methyl-2,5-dimethoxybenzaldehyde: 1.000g, 5.55mmol, prepared as per previous post) is suspended in twice its mass of nitroalkane (1-nitropropane: 2.000g actual used, 2.022g, 22.7mmol, 4.09eq, ≥99% reagent grade) and then according to Traschel, 2% of that reaction mass is added butylamine and acetic acid.

Cyclohexylamine was used instead, theoretically required 3x0.02=0.06g CHA and 0.06g AcOH, actual used, 118mg CHA, 1.14mmol, 0.187eq -- 304mg AcOH, 5.07mmol, 0.912eq.

Our usual is typically 0.1eq of the amine base (10mol%) in an excess of acetic acid solvent, but reportedly the use of excess nitroalkane gives superior yields. We are unsure why exactly, but most likely forcing equilibrium by a large excess of the nitroalkane. This also minimizes side reactions, such as unwanted condensations. Further, nitroalkane is mildly acidic which promotes dehydration of the beta-nitroalcohol that forms (though with the presence of acetic acid/acetate salt, the acetic acid is the main catalyst). 

This suspension was briefly boiled over a free flame to dissolve the solids, during which the reaction rapidly turned orange and drops of water were seen condensing in the flask (they do not mix into the reaction). The flask was then heated for 6 hours (shulgy does 24h with a Barret-Trap, Traschel does "until TLC" which is around 2h) at an oil bath temperature of 130c (slight reflux, could probably be conducted in a sealed vessel instead) and left to sit at room temperature for a day (did not have time to do workup)

The flask, now with a reddish orange solid was placed on the rotovap at strong vacuum (around -95kpag)and with quite a bit of heat (boiling water bath) until no more solvent distilled (few min), then was dissolved in about 80-100ml ether and washed consecutively dil HCl (10ml water + 1x"2ml" pipette of 5M HCl), 10ml dil NaOH (10ml water +0.5x"2ml" pipette of 25%ww NaOH), 20ml brine. Stopper and sep funnel rinsed with additional ether.

The pooled organics were dried (MgSO4) with care to rinse the drying agent and cotton plugged funnel with ether after, rotovapped, recovering 1.4g of a reddish orange crystalline powder.

The solid was dissolved in about 10ml boiling not-quite-anhydrous IPA and cooled in a RT water bath (slower cooling would be preferred- larger crystals are superior in purity and to filter). The result was broken up and rinsed with 10ml 75%vv IPA, and filtered by suction. The flask was rinsed with water and added to the filter, then the solids were patted with a spatula and rinsed with more water. It was sucked on the filter for a while then dried to constant mass (vacuum oven ~100c few min, hot spot in the oven resulted in a little bit of it melting in the vial) furnishing 0.900g of orange crystalline solid, strong yellow fluorescence, MP around 115c. (72% yield)

Commentary: The yield was 72% which is excellent, and undoubtedly some loss may be attributed to physical losses (see last image) as we were not as diligent as we thought. However, this yield beats that of shulgin's (31.6g aldehyde = xpct'd 44.06g NB, 19.6g actual = 62% yield). Partly we suspect this is due to the lack of acetic acid used and the benzene effectively lowering the reaction temperature, though paradoxically we may also have expected a better yield due to lower temp and less sidereactions. It may very well be the fact that it was not ran long enough, but we are unsure. Regardless Traschel's procedure (though with our slight changes) yielded higher by 10%, and considering the scale we ran plus visible points of physical loss (and including that in the IPA and stuck to the Buchner funnel), this procedure likely gave reaction yields above 70%, perhaps even 80%.