Sciencemadness Discussion Board

Copper(II) reduction

Linus1208 - 9-8-2021 at 11:13

So I need to reduce Copper(II) oxide to Copper(I) oxide, I managed to do it by heating it with a bunsen burner, but I don't feel like using up a whole gas cartridge just for a few grams of Copper oxide.

I read on wikipedia that it can be reduced in an alkaline solution (ammonia?) with aldehydes, so my question is, can I reduce it with glucose, as it is an aldehyde.

Also, as currently my only glucose source is corn sirup, which has a lot of impurities, will it work if I heat Sucrose with HCl for a few minutes, so it gets split to glucose and fructose (the fructose shouldn't be a problem) and use that for reducing (of course after drying it, I don't want to fill everything with white NH4Cl smoke :P )?

Thanks for replys!

Morue - 9-8-2021 at 13:03

An easy way to achieve this is to form what is known as Benedict's reagent from CuSO4, sodium citrate and sodium carbonate and reduce it with glucose or fructose to form copper (I) oxide.

I tried another method a while ago using copper acetate. I dissolve basic copper carbonate in 10% acetic acid. I made sure to have excess acetic acid to have excess acetate ions in solution after addition of Na2CO3. Then I added dropwise a concentrated solution of Na2CO3 until a pH of around 11 to litmus paper. I obtained a dark blue solution with no precipitation of basic copper carbonate. I added blueberry honey and heated the solution gently with a warm water bath. Formation of copper (I) oxide was observed by the apparition of a brick red precipitate. I also tried maple syrup instead of honey and no reaction was observed. My conclusion is that this method does not work with glucose (or maybe it does, but very very slowly), but appears to work with fructose.

Hope this helps.

Linus1208 - 9-8-2021 at 13:12

Quote: Originally posted by Morue  
An easy way to achieve this is to form what is known as Benedict's reagent from CuSO4, sodium citrate and sodium carbonate and reduce it with glucose or fructose to form copper (I) oxide.

I tried another method a while ago using copper acetate. I dissolve basic copper carbonate in 10% acetic acid. I made sure to have excess acetic acid to have excess acetate ions in solution after addition of Na2CO3. Then I added dropwise a concentrated solution of Na2CO3 until a pH of around 11 to litmus paper. I obtained a dark blue solution with no precipitation of basic copper carbonate. I added blueberry honey and heated the solution gently with a warm water bath. Formation of copper (I) oxide was observed by the apparition of a brick red precipitate. I also tried maple syrup instead of honey and no reaction was observed. My conclusion is that this method does not work with glucose (or maybe it does, but very very slowly), but appears to work with fructose.

Hope this helps.



Thanks for your answer.

I just read fructose is also a reducing sugar, so I guess the glucose / fructose mix should work.

Also after doing further research on youtube, I found a few synthesis that reduced copper(II) hydroxide (made from NaOH and CuSO4*5H2O) with glucose.
I guess this would be ideal for me, as I got my copper(II) oxide from CuSO4 by thermal decopmosition, so I can make it more efficient by leaving out the thermal decomposition step and avoid breathing healthy SO3 gas from the decomposition :P

Bedlasky - 9-8-2021 at 13:45

Yes, you can sucrose for this. Mix sucrose with tartaric or citric acid and boil it for 10 minutes to hydrolyse sugar to glucose and fructose (benefit of these acids is that tartrate/citrate serves as complexing agent for Cu(II) in alkaline solution, but it isn't necesary to use them, because glucose and fructose form soluble complexes with Cu(II) as well). Cool solution and add NaOH or Na2CO3 until pH of your solution is strongly alkaline. Don't use ammonia or NH4HCO3, Cu2O is soluble in these forming colourless [Cu(NH3)2]+ ion. Then dissolve CuO in this mixture and heat it for a while. Cu(II) is reduced to Cu(I) by glucose and fructose quickly even at room temperature, but heating speed things up. Then filter orange Cu2O and dry it (during drying will Cu2O turn red).

Why did you make CuO by thermal decomposition of CuSO4? There are easier ways... Precipitate Cu(OH)2 from CuSO4 solition and heat it for a few minutes (Cu(OH)2 decompose at 80 °C), then filter.

Morue: Glucose react with Cu(II) fairly quickly. Not that quickly as fructose, but in manner of few minutes at RT (and practicly immediately in hot solution).

[Edited on 9-8-2021 by Bedlasky]