Twice now, I've had the opportunity to work with potassium metal. The first, I attempted NurdRage's potassium metal synthesis by catalytic reduction
of KOH with Mg using tert-butanol, and I succeeded in making a small amount of the potassium metal. I added it to acetone (having had no toluene
present, and not realizing that it would react), and it formed a deep red, milky solution that was extremely basic. Today, having ordered some
potassium metal and wanting to clean its surface before ampouling it, I again, had some small pieces left over, and wanted to see if I could replicate
my first result. Again, I got the milky, red solution. I tried again with MEK, and it took longer, but I got the same type of red solution. I'm at
a loss for what this might be. I've been googling this all day, but I can't seem to find any reference to this type of red coloration. Does anyone
have any idea what's going on here?
Thanks in advance!Paddywhacker - 26-2-2013 at 23:43
Google the Aldol condensation. Even mild alkalis such as are present in molecular sieves will catalyse the polymerisation of acetone.DraconicAcid - 26-2-2013 at 23:50
That reminds me of back when I was an undergraduate, doing a Wittig reaction for organic chem. I was refluxing an alkali metal in some alcohol, and
my condenser broke. So I replaced it with one from the storeroom, and used it as-is, without cleaning it or anything (I'd hate to use a wet condenser
for this, obviously).
Once the solution was refluxing, every drop of liquid that condensed and dripped into the solution turned an intense red, which quickly faded. My
initial horrific thought was, "Crap! My condenser's bleeding!!" If I ever figured out what it was, I quickly forgot about it (since I had no way of
knowing what was contaminating the condenser), but now I think it might have been traces of acetone.Nicodem - 27-2-2013 at 07:21
Google the Aldol condensation. Even mild alkalis such as are present in molecular sieves will catalyse the polymerisation of acetone.
Yes, into a gunky mass.
Strong acids can also result in self-condensation, mainly forming pherone, among other products. I still am not aware of any good explanation for the
color change.
So, yes, acetone is not stable for any length of time if the pH is too high or too low.
If I can make a suggestion, the reduction of acetone with elemental sodium might be able to work if a buffer is used, such as hydrated alumina, to
prevent the pH from going too high. Ideally the buffer should actually be dissolved in the solution, or at least well dispersed.
Or what about just doing the reduction with Al amalgam?
[Edited on 27-2-2013 by AndersHoveland]Adas - 27-2-2013 at 13:12
