SpicyBrown (Hive Bee)
12-27-01 21:40
No 250792
      Problem encountered during Nitroethane synth.  Bookmark   

SWIM had a dream about making nitroethane. It seemed to go ok, but when distilling to isolate the nitroethane at the end some wacky white semisolid ... slime formed inside the condensor and the yield was bad. SWIM seemed to think the slimy stuff was sort of holding up a lot of liquid, especially given the smell coming from the condensor afterwards.

Here is the dream.

40.00g of Ethyl Bromide (Around 30 ml) freshly dried over MgSO4 was put in an addition funnel.

250ml DMSO was put in a 1000ml beaker and 44.44g dry lab grade NaNO2 was added. About 50 more ml of DMSO had to be added to get all the NaNO2 to dissolve. It was pretty cold where SWIM was working and SWIM had to warm up and melt the DMSO to get it out of the bottle.

With the beaker placed in a cold water bath, began dripping the Ethyl Bromide onto the DMSO/NaNO2 solution, with manual stirring (Damn magnetic stirrer was somewhere else..). This formed little wisps of white when the drops would hit, which would quickly go into solution. The addition took 10 minutes, with the temperature staying below 27C.

About 6 minutes after the addition stopped, a lot of thicker wisps of white precipitate began to form. A couple of minutes later the whole beaker was a funky slimey semisolid white mass. More stirring of this sludge caused the temperature to rise to 29C, so SWIM let it fall and would slowly stir every now and then until temperature hit around 26-27C. About 15 minutes later the temperature stopped increasing with the stirring, so SWIM removed it from the water bath. The temperature continued to fall. The sludge looked like real thick tapioca pudding, cream colored.

SWIM then filled the beaker to about 550ml with di H2O. This caused the temperature to jump up to 35C(!) so SWIM put the beaker back in the water bath. Occaisionally stirred this solution (which was slowly going completely to solution) keeping temperature under 30C. About 10 minutes later the temperature stopped increasing, and the solution was a clear off-yellow color.

This ~550ml solution was divided in two, since SWIM's biggest sep. funnel is 500ml..
Each half of the solution was shaken vigorously 3x75ml DCM, and all 6 separations was combined.

SWIM realized shortly after waking from this dream that here's where SWIM forgot to was the combined DCM with di H2O... Suppose this could cause problems..

The cloudy DCM was dried over a .. large amount of MgSO4, and filtered. The filter was rinsed with ~50ml DCM.
The ~500ml DCM, which was now a very clear off-yellow was placed in a 1000ml round bottom flask and joined with an apparartus setup for distilling, with a 200mm vigreaux fractioning column and an around-200mm condensor.

The flask was set in a heating mantle and the distillation began. The DCM came over, followed by a lot of intermediate fractions.
When the temperature was around 90-100C, SWIM noticed little white specks in the top of the condensor.

When the temperature crept up to 113C, the remaining solution in the boiling flask was deep yellowish-orange, with the distillate being mostly white(clear). The receiving flask was swapped to collect the nitroethane fraction.

Now a little bit of creamy-white colored sludge was noticed in the top of the condensor. The distillate was collected until temp said 120C, but a lot of liquid was clinging to the sludge and stuck in the condensor. By the end of the collecting, a little bit of the sludge made it's way to the receiving flask.   The small amount of collected liquid boiling within 114-120C was tinged yellow. The liquid poured away, very easily leaving the sludge behind stuck to the flask bottom. Weight was 5.24g of very powerful (Or maybe SWIM just took a big whiff.. Eek), sickly sweet smelling liquid.

The liquid still in the boiling flask is now almost deep red in color.

Has anybody experienced this problem with the condensor sludge before? What can SWIM do to try
to get more nitroethane out of the sludge? It smells very strongly like the collected liquid. For now, it's still stuck inside the condensor until SWIM dreams what to do with it. Could [accidentally] skipping the DCM water washes have been caused SWIM's problem?

(Master Whacker)
12-28-01 00:52
No 250830
      Re: Problem encountered during Nitroethane synth.  Bookmark   

I don't know about that sludge, but I do know you can certainly get those yields up by including a mole of phloroglucinol(expensive) or catechol.  These phenols scanvenge yield-killing -ONO compounds.  Refs are available here at the hive and there is also a good write-up in TSII by yours truly on this exact rxn.
(Hive Bee)
12-29-01 13:21
No 251095
      Re: Problem encountered during Nitroethane synth.  Bookmark   

Thanks for the tip, SWIM will look into catechol the next time around. Dunno what that sludge was. It was a real bitch to clean out of the glassware, and it smelled absolutely horrible. SWIM thinks that not washing the DCM with water may have led to problems. SWIM diluted the leftover mixture from the boiling flask which was now really deep reddish-brown with DCM, and then added some water to see what it did; It took on the nasty color quite well. Well, first attempt always has good messups to learn from.