Sciencemadness Discussion Board

What yields more

B(a)P - 2-7-2020 at 14:01

What is the reaction? I would have thought more solid on the bottom of the reaction vessel would reduce bumping as in would provide gas nucleation sites? The more you filter the more mechanical losses that you have so that will reduce yield.
Your only question is about volume, of course if solid is removed then volume decreases, what do you mean by this?
I see no reason why multiple filtrations would improve yield if that is your question. It may depend on the specific reaction though.....

Texium - 2-7-2020 at 16:12

On this forum we appreciate clear language and references to procedures.

When those aren’t provided, it’s a lot harder to help, and it gives the unshakable impression that you’re up to something unsavory. You can’t expect anyone to advise you on a problem so vague. The answer could go either way depending on what it is specifically that you’re making, so either enlighten us, or this will go to Detritus.

Yttrium2 - 2-7-2020 at 17:11

Wikipedia says:

"K2HPO3 + 2 HCl → 2 KCl + H3PO3
In practice aqueous potassium phosphite is treated with excess hydrochloric acid. By concentrating the solution and precipitations with alcohols, the pure acid can be separated from the salt."


Now, I have heard that it is best to remove precipitation, reduce the solution, remove more precipitate, reduce the solution, remove more precipitate -- I've heard its best to do this like six times in order to reduce bumping, but it seems like an awful lot of work, mess, smell ect. Is this the best way to produce the H3PO3?


What about boiling it almost all the way, till it stops precipitating and then filtering, and then reducing the mixture? Will this have more mechanical loss since you are filtering very little liquid through a lot of KCL or would there be more mechanical loss through filtering a lot of liquid through a little KCL mutliple times? -- Nothing was said about the mechanical losses, just the bumping.



What about freeze distilling the h3po3 out of solution?


What about setting up for distillation, reducing the mixture till all the precipitate forms, and then vacuum distilling out the H3PO3?


I am not up to anything unsavory
P.S. - I would like my name changed to IUPAC

[Edited on 7/3/2020 by Yttrium2]

SWIM - 2-7-2020 at 17:31

This is an unusual case since the solution is in phosphoric acid.

As you boil the water out it'll get thicker and thicker, and the thicker solution will make it harder to filter the KCl.

The extra filtrations may be to avoid winding up with a whole lot of KCl in a thick phosphoric acid syrup because filtering this might be tough.

Do you have a vacuum filtration set-up?
Could save a bit of time.

Yttrium2 - 2-7-2020 at 17:36

I guess the alcohol is used to wash the phosphorus acid / water off of the KCL

isopropyl alcohol


In addition, it forms an azeotrope at certain levels (how much again?) - with water and helps to dry the phosphorus acid at lower temperatures.

[Edited on 7/3/2020 by Yttrium2]

Yttrium2 - 2-7-2020 at 17:38

Just confused about the bumping,

is it true that stirring is always recommended and boiling stones never? I heard this somewhere

Yttrium2 - 2-7-2020 at 21:03

Quote: Originally posted by SWIM  


As you boil the water out it'll get thicker and thicker, and the thicker solution will make it harder to filter the KCl.

The extra filtrations may be to avoid winding up with a whole lot of KCl in a thick phosphoric acid syrup because filtering this might be tough.



does this make it easier, in practice?

draculic acid69 - 3-7-2020 at 01:31

So r u making h3po3 from a potassium phosphite solution? Is that what this post is about?

mackolol - 3-7-2020 at 01:49

I totally don't agree with you that if you have more solid on the bottom, the reaction doesn't bump. Lately, I'm performing decarboxylation of aminoacid by boiling it in turpentine. The aminoacid has quite low density and it is required a lot of this to get few grams, so the solvent layer is just above. All I can tell you is that it bumps as fuck.
If I had to tell how to prevent bumping, the solid should be dense and hard, something like sand and just a thin layer to cover the bottom.
@Yttrium2 is right, stirring is always recommended.

Yttrium2 - 3-7-2020 at 07:20

Quote: Originally posted by mackolol  
I totally don't agree with you that if you have more solid on the bottom, the reaction doesn't bump. Lately, I'm performing decarboxylation of aminoacid by boiling it in turpentine. The aminoacid has quite low density and it is required a lot of this to get few grams, so the solvent layer is just above. All I can tell you is that it bumps as fuck.
If I had to tell how to prevent bumping, the solid should be dense and hard, something like sand and just a thin layer to cover the bottom.
@Yttrium2 is right, stirring is always recommended.



who were you disagreeing with, swim wasn't sure.

and

what do you mean by "If I had to tell how to prevent bumping, the solid should be dense and hard, something like sand and just a thin layer to cover the bottom"


-




If anyone else feels like chiming in I am waiting

draculic acid69 - 3-7-2020 at 22:36

I'm still not sure what this post is about

B(a)P - 4-7-2020 at 01:38

Yttrium2 appears to have deleted the original post, which makes this very confusing.
Yttrium2, why not try both and compare yields then report back? That would answer your question and contribute to the forum.

Yttrium2 - 5-7-2020 at 17:22

My last question is how come the KCL does not stay in the water / H3PO3 / acid after it has been reduced down, and filtered off.

I know a lot of KCL precipitates at first, but doesnt some of it stay dissolved and make its way into the final product?

Unless one is boiling it all the way down, and just filtering off the H3PO3 -- but there is usually a minimal amount of water in it at this point, which I suspect would contain some dissolved KCL

Is the alcohol addition essential to get the dissolved KCL to precipitate from the trace amounts of water in the H3PO3?

Yttrium2 - 5-7-2020 at 19:36

and what about the phosphite solutions that have dyes in them? I heard that the main source changed their label, but did not change the formulation, -- can anyone comment on that? I forgot the color of the original solution and dont know if it had dye in it.

[Edited on 7/6/2020 by Yttrium2]