Sciencemadness Discussion Board

making Cu(OAc)2

Actinium - 18-9-2014 at 10:52

I made a solution of 1 part 80% Acetic acid to 1 part 3% H2o2. obviously the amounts are not stoichiometric. The reaction took aprox 1-2 minutes to get going and proceeded very nicely at about 30 minutes in for a couple hours where only slight warming was noticed. the liquid has taken on a deep and brilliant blue color. another ml of 3% H2o2 was added 5 hours and 24 hours after the reaction slowed down.
yesterday I added another ml of 35% H2o2 and the reaction although brief started very quickly.
Ill try to post some pics.
In this sort of reaction is the H2o2 used primarily as a catalyst to kick start the reaction and is peroxyacid the primary component that forms the acetate or a convenient biproduct or two chemicals that happen to be used for this experiment?

bbartlog - 18-9-2014 at 11:32

Where does the copper come in?

So far as your question goes: acetic acid by itself doesn't react with copper, because it's in the zero-valent state, Cu(0), and acetic acid is not an oxidizing acid. But it does react with copper oxide to form the acetate (and water). So the peroxide here is acting to oxidize the exposed copper surface, which then reacts with the acetic acid and dissolves. The peroxide is used up in the process, so its function here is not catalytic, it's part of the reaction.



Actinium - 18-9-2014 at 13:29

thank you for clarifying and patiently taking the time to explain this to me.
Would it therefor be advantageous to either have a stronger solution of peroxide or if using a dilute solution of peroxide use a dilute solution of acetic acid? would having a weak H2o2 solution not cause enough Cu(o) to form prior to being turned to an acetate by a conc. CH3COOH solution?

Texium - 18-9-2014 at 13:45

When I tried this reaction, I only had 9% acetic acid and 3% peroxide. I used a large amount of each of them, and over the course of a few days, it reacted enough to noticeably shrink the width of the copper wire that I used in the reaction. I didn't bother to calculate any ratios, because I simply wanted to make some, just to have it. I don't think the concentration really matters a whole lot, but it will greatly affect the amount of time it takes to evaporate off the water.

Actinium - 18-9-2014 at 13:54

thanks for the reply.
What is the insoluble at the bottom of the flask? Just out of curiosity? The Cu(OAc)2 is still in solution at this point.

Texium - 18-9-2014 at 13:59

Is it white? When I made mine there was a strange white suspension. I wasn't sure what it was, but it filtered out quite easily, and when it was gone the solution was much clearer and darker.
At first I thought it was copper hydroxide that looked white compared to the blue solution, but that would have reacted with the acetic acid. My current guess is that it's some organic impurity in the acetic acid that was oxidized by the peroxide, somehow causing it to become insoluble.
I'll try letting a solution of acetic acid and hydrogen peroxide sit out with nothing else added to it and see if the white precipitate appears.

Actinium - 18-9-2014 at 14:04

yup its white and makes the solution cloudy as soon as I stir it, but settles very quickly.

I got home from work and decided I was going to dump about ~3ml (eyeballed it), of 35% H2o2 and started reacting vigorously instantly. The white precipitate at the bottom started clumping up and either floated to the top before disolving back into solution or did so on it's own.
-Ac-

[Edited on 19-9-2014 by Actinium]

Amos - 18-9-2014 at 21:02

I had a similar issue to this, though my precipitate was more bluish-green in its own right. Copper(II) chloride will react with copper metal to produce insoluble Copper(I) chloride in the same reaction with hydrochloric acid instead of acetic acid. Searches do seem to point to the possibility of copper(I) acetate, I even found a vague synthesis here: http://onlinelibrary.wiley.com/doi/10.1002/047084289X.rc193/...

That or it could maybe be basic copper(II) acetate, another obscure compound I've heard about but couldn't find much info on. This one is a component of verdigris, which traditionally was made by treating copper sheets with vinegar.

Whatever the case, trying to filter out the precipitate seemed to be futile for me. About the same amount formed on the bottom within the same day that I filtered it out, which I suspect meant I was just wasting more of my copper ions. One day I decided to boil the solution of copper(II) acetate I had been working on all the way to dryness. The precpitate disappeared and I got a glittering blue-green powder in the end that I was quite happy with.

DraconicAcid - 18-9-2014 at 21:04

Quote: Originally posted by No Tears Only Dreams Now  
I had a similar issue to this, though my precipitate was more bluish-green in its own right. Copper(II) chloride will react with copper metal to produce insoluble Copper(I) chloride in the same reaction with hydrochloric acid instead of acetic acid. Searches do seem to point to the possibility of copper(I) acetate, I even found a vague synthesis here: http://onlinelibrary.wiley.com/doi/10.1002/047084289X.rc193/...


Copper(I) salts that are not insoluble in water are water-sensitive; they disproportionate to give copper metal and copper(II) salts.

bbartlog - 18-9-2014 at 21:10

Quote: Originally posted by DraconicAcid  

Copper(I) salts that are not insoluble in water are water-sensitive; they disproportionate to give copper metal and copper(II) salts.


I know that's true for cuprous acetate, but is it actually general? Cuprous chloride is situationally soluble in water - there are a variety of other salts you can add to increase its solubility and in any case it's slightly soluble in boiling water by itself. And it doesn't disproportionate, though it's certainly air-sensitive...

DraconicAcid - 18-9-2014 at 21:30

Quote: Originally posted by bbartlog  
Quote: Originally posted by DraconicAcid  

Copper(I) salts that are not insoluble in water are water-sensitive; they disproportionate to give copper metal and copper(II) salts.


I know that's true for cuprous acetate, but is it actually general? Cuprous chloride is situationally soluble in water - there are a variety of other salts you can add to increase its solubility and in any case it's slightly soluble in boiling water by itself. And it doesn't disproportionate, though it's certainly air-sensitive...


When you add salts to make it soluble, you're dissolving it as a complex ion, which is stable towards disproportionation. But the simple aqueous ion isn't stable.

Amos - 19-9-2014 at 05:07

Quote: Originally posted by DraconicAcid  
Quote: Originally posted by No Tears Only Dreams Now  
I had a similar issue to this, though my precipitate was more bluish-green in its own right. Copper(II) chloride will react with copper metal to produce insoluble Copper(I) chloride in the same reaction with hydrochloric acid instead of acetic acid. Searches do seem to point to the possibility of copper(I) acetate, I even found a vague synthesis here: http://onlinelibrary.wiley.com/doi/10.1002/047084289X.rc193/...


Copper(I) salts that are not insoluble in water are water-sensitive; they disproportionate to give copper metal and copper(II) salts.


Ah, well that rules out the first idea. The wikipedia article on copper(II) acetate does mention basic copper acetate as being poorly soluble in water.

mr.crow - 23-11-2014 at 10:47

What a pain in the butt. I'm just going to buy some now instead.

I finally had my copper acetate solution boiled down to a manageable volume. I added extra water to dissolve some random crystals that formed and filtered it so its perfectly clear. There was a huge problem with insoluble gunk and precipitates during this process so I was happy to have a beautiful clear blue solution.

When I heated it up the whole thing decomposed into teal colored gunk :mad: I guess that's your basic copper acetate.

DrMario - 23-11-2014 at 13:14

Quote: Originally posted by mr.crow  
What a pain in the butt. I'm just going to buy some now instead.

I finally had my copper acetate solution boiled down to a manageable volume. I added extra water to dissolve some random crystals that formed and filtered it so its perfectly clear. There was a huge problem with insoluble gunk and precipitates during this process so I was happy to have a beautiful clear blue solution.

When I heated it up the whole thing decomposed into teal colored gunk :mad: I guess that's your basic copper acetate.

You have to heat the solution very carefully, to obtain the monohydrate. Which is, BTW, teal. If you are really careful, you can obtain the anhydrous compound which is greener.

Metacelsus - 23-11-2014 at 14:45

A few years ago, I was trying to make anhydrous copper acetate from the monohydrate. Heating it at atmospheric pressure doesn't work; it loses acetic acid to make basic copper acetate. However, under vacuum, I was able to dehydrate a small amount by heating. According to a patent in the acetic anhydride thread, heating of anhydrous copper acetate gives acetic anhydride (that's why I originally wanted anhydrous copper acetate). However, I never got enough anhydrous copper acetate to test it, and I eventually discovered I could just buy acetic anhydride from Elemental Scientific.

DraconicAcid - 23-11-2014 at 15:09

If you have coppery crap, precipitate it as the carbonate (wash it with alcohol to make it manageable), then dissolve the carbonate in your 80% acetic acid, and put it in ice to get it to crystallize as the monohydrate. If it doesn't crystallize, try adding isopropanol and cooling again.