Sciencemadness Discussion Board

Potassium rhodizonate

innervision - 8-7-2015 at 18:36

I've been playing with lead compounds lately and I wanted to synthesize this salt to make sure I am cleaning up properly.

I followed the video on NurdRage's youtube channel but used a rb flask with reflux condenser, heated by an oil bath.
Everything was going fine until I decided that my oil bath was relatively stabilized to give a gentle reflux, and left it unattended for about an hour. When I came back, the oil bath was 165C, and the solution looked black and was boiling pretty good with no more signs of NO2. I turned down the heat and left it for another hour. The solution upon swirling in flask was orangey yellow, but so intensely as to look black.

I continued the experiment to see if I would still get a precipitate from the KC2H3O2. There was a precipitate and it was very dark; not reddish like it should be. It was not soluble in alcohol.

My question is, did my lack of temperature control form croconic acid instead?

Boffis - 9-7-2015 at 14:40

No croconate of Na an dK are orangy coloured but sodium and potassium rhodizonates are almost black sparingly soluble in pure alcohols but more soluble in water giving deep yellow solutions that slowly fade on standing. It doesn't really matter what the temperature of the oil bath was providing the reflux system could cope with the increased reflux rate.

If you want sodium croconate use NaOH instead of potassium acetate and then precipitate the croconate as the ochre yellow barium salt and work up from there.

innervision - 10-7-2015 at 00:41

I tried this procedure again keeping the reflux temp around 100C. Everything was going nicely and by 2.5 hours, NO2 had ceased and the solution was nice and clear. I let it go another 30min to give it 3hrs reflux as specified and when I checked on it, it was darkening on me again. I think that if I try this again, I will keep the temp lower yet and stop reflux once the solution becomes clear and NO2 evolution ceases.

I have no idea what is forming when the solution darkens. It doesn't darken on the nurdrage video.

I finished up the procedure with the just starting to darken solution and I have a few grams of deep violet crystals that give bluish silver, glittery sparkles in light. Very cool looking.
In the video, they looked brownish red, but maybe that is lighting? Neither look almost black though.