stoichiometric_steve - 29-10-2007 at 08:56
after the reduction of 2,5-dimethoxy-ß-nitrostyrene using NaBH4 and subsequent workup (removing water soluble salts), i ended up with a yellow oil
mixed with a lot of a white, probably crystalline substance.
since i have not found any physical data for 2,5-dimethoxyphenyl-2-nitroethane, i am not sure whether this is the desired product or not.
upon digesting the mixture with MeOH and keeping it in the fridge for a few days, more solids aggregated.
all NaBH4 double bond reduction writeups for this substrate state that the reaction yields a yellow oil, so i'm not sure whether the solid mass
obtained is the dimer or some other undesired product.
ssdd - 29-10-2007 at 09:15
I am not sure what type of equipment you have on hand or if you are doing this at home, but they way I would deturmine this is as follows.
Take a small sum of the crystalline powder and run it through a GC/MS. This should give the atomic weight of the crystal, if you know the atomic
weight of your product you can make a guess as to if its impurities or the product. This has worked for several intermediates in a research project I
am working on when I had an unknown large crystal fall from solution.
hope this helps,
-ssdd
Klute - 29-10-2007 at 09:49
Try melting the crystals, they could inorganic salts from the borohydride reduction, I remember this beeing mentionned at the hive a couple of times.
IIRC, Barium reported this nitroalkane as been obtained as a yellow oil, but that could crystallize at room temp when sufficiently purified. If it
melts at a low mp, it's urely the nitroalkane, otherwise it could be boron salts.
stoichiometric_steve - 29-10-2007 at 10:02
yeah ssdd, if only i had a GC/MS... 
TLC will have to do. i'll try to take a m.p.
asap.
jam640 - 29-10-2007 at 10:09
Yes, most likely boron salts. They have a tendency to precipitate after a while unless extensive care is taken during the workup after reduction.
Sucks. 
Klute - 29-10-2007 at 13:37
Can't you distill that one too? Or did you simply want to check the crystals were some nitroalkane?
stoichiometric_steve - 29-10-2007 at 22:11
as already stated, it is quite unlikely that the solids are boron salts, since the organic phases were carefully washed after the reduction. i think
the solids are soluble in acetone...
Klute - 30-10-2007 at 06:50
Coming to think of it, I also had some very fine whitish solids with a nitroalkane... When recrystallizing from MeOH, threy caused turbidity, but were
impossible to filter through regular filter paper, glass frite, or porous membranes. I just left them there. The nitroalkane had been washed too. I
considered them as some dimeric impurities. But it was a small amount.
How many BH4- eq. were used? 4x or less? Did you try weighing the obtain solids? Maybe all the oil crystallized... If it is the nitroalkane, then it
must be quite pur, and gives a possibility of purifying further, without distillation. Congrats!
transformer - 30-10-2007 at 07:55
The pure nitroethane is white
stoichiometric_steve - 30-10-2007 at 12:07
but is it a solid or liquid, vaguuh?
transformer - 31-10-2007 at 10:13
It is a solid at rt.
Klute - 1-11-2007 at 02:27
Bingo! So this nitroethane is possible to recrystallize.. Thanks alot Vaguuh!