Sciencemadness Discussion Board

preparation of pure potassium pyrosulfate

Assured Fish - 14-2-2017 at 21:17

I feel like this is the kind of question that should already be on the forum but i searched for it and couldn't find jack squat, i also googled the hell out of it and again couldn't find anything.
So im asking you guys whom i am sure have either synthesized it or used it given how regularly its used as an oxidizing agent in certain preparation. How would i go about preparing some pure potassium pyrosulfate?
According to Wiki it is made by thermal dehydration of potassium bisulfate and so i went and melted some swimming pool grade potassium bisulfate in a test tube and of coarse it melted which was expected given that it melts at around 200*C however it also started to give off alot of bubbles which i presume is H2O indicating decomposition, According the the Wiki entry for sodium bisulfate it decomposes before 300*C so am i just supposed to heat this stuff until it stops giving off bubbles of H2O or should i really be monitoring the temperature until it reaches say 350*C?

Now this stuff is also soluble in water however im sure that it would undergo hydrolysis back to bisulfate if its in contact with H2O for any extended period of time, so is there a better solvent from which i could recrystallize this stuff.

https://en.wikipedia.org/wiki/Potassium_bisulfate

https://en.wikipedia.org/wiki/Potassium_pyrosulfate

I intend on using it in the following prep for synthesizing pyruvic acid from tartaric acid.

http://www.prepchem.com/synthesis-of-pyruvic-acid/

Also is there any way for me to test for the presence of pyrosulfate?
Cheers

Magpie - 15-2-2017 at 10:37

Len1 in Prepublication shows how to make SO3 from NaHSO4. He starts by making sodium pyrosulfate, Na2S2O7. There may be something useful for you there if making K2S2O7 can be considered analogous:

http://www.sciencemadness.org/talk/viewthread.php?tid=10332


[Edited on 15-2-2017 by Magpie]

JJay - 16-2-2017 at 01:03

Wow, he had to evacuate his lab when his fume hood was overwhelmed by SO3 vapors!

Aqua-regia - 16-2-2017 at 07:02

If i remember right, K-metabisuflite (also known as E224 OTC product), can oxidizing with HNO3 to pyrosulfate. Iam not entirely sure needing fuming or common nitric acid. Try to do it in small large in crucible. If you heating this with strong burner, first nitrous gases, after that SO3 ceases.

K2S2O5+2HNO3——>K2S2O7+NO+NO2+H2O

[Edited on 16-2-2017 by Aqua-regia]

Assured Fish - 17-2-2017 at 14:23

Thank you for the info guys, I wasn't aware how dangerous this procedure was actually going to turn out and i may need a fan to blow any SO3 vapors away from me if i plan on doing this in a crucible.
Quote:

If i remember right, K-metabisuflite (also known as E224 OTC product), can oxidizing with HNO3 to pyrosulfate. Iam not entirely sure needing fuming or common nitric acid. Try to do it in small large in crucible. If you heating this with strong burner, first nitrous gases, after that SO3 ceases. K2S2O5+2HNO3——>K2S2O7+NO+NO2+H2O


This idea actually look promising as i have over 700mls of fuming nitric acid on hand i thinks its around 64%. "first nitrous gases, after that SO3 ceases" I think you mean first nitrous gases are given off then that ceases and SO3 start to be given off from the decomposition of the pyrosulfate.
Im still looking for an appropriate solvent to try and recrystallize it from and the stuff i heated in the test tube has caked itself to the glass almost like glass itself and requires water to get it out.

Aqua-regia - 18-2-2017 at 03:16

Hi, during the oxidation ceases nitrous gases, after the process you have dry white pyrosulfate. This is decomposes just above 600 C deg. This methode is expensiv and wasting your HNO3.


Prepare KHSO4. Or buy it . This is cheap and free. Over 300 C degrees decomposes:2KHSO4 ——> K2S2O7 + H2O

Good luck.