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Copper Tartrate

nlegaux - 25-12-2014 at 12:42

I haven't been able to find any (useful) information on Copper Tartrate. The only information I could find was on the wikipedia page about Tartaric acid (http://en.wikipedia.org/wiki/Tartaric_acid), where it mentions that tartaric acid forms a complex with copper. Does anyone have any good information on this complex?

Out of curiosity, I added Potassium Bitartrate to a CuSO4 solution (excess of CuSO4). The solution turned a pale blue color. When IPA was added, a pale blue non-crystalline precipitate formed. Is this Copper Tartrate?

Thank you,

nlegaux

Metacelsus - 25-12-2014 at 19:20

Tartaric acid and copper are used in the biuret reagent; tartaric acid and copper definitely form a complex. Copper tartrate should be isolable, but I'd prepare it by directly reacting tartaric acid with copper hydroxide.

Amos - 25-12-2014 at 19:21

I have made a deep blue complex, similar to the tetraammine copper(II) complex but without any hint of violet coloration, by adding potassium/sodium tartrate to a solution of copper(II) sulfate and heating. The tartrate I believe was produced by adding sodium carbonate to an excess of potassium bitartrate in solution. I wish I had kept some notes on that...

Paddywhacker - 25-12-2014 at 20:45

I once made some by dissolving copper(II) oxide in aqueous tartaric acid. The two were in stociometrically equal amounts and the container was heated in a pressure cooker for 30 minutes.

All of the black oxide dissolved to give a pale blue precipitate that was soluble in excess potassium hydrogen tartrate solution. Somebody suggested that I had the basic tartrate salt, but I don't believe that. So the straight salt was only sparingly soluble, but it dissolved in excess tartrate to form the usual complex. The complex should have also been stable to alkali, but I didn't test for that.

A similar experiment with citric acid was similar, but not all of the copper oxide dissolved.

nezza - 26-12-2014 at 02:00

Copper sulphate and Sodium potassium tartrate (Rochelle salt) form the basis of Fehlings solution which is a classic test for reducing sugars. The mixture is boiled and copper(I) oxide is formed as a yellow/red precipitate. The tartrate keeps the copper ions in solution in an alkaline solution by complexing with the copper.

Dr Corvin Ravenden - 13-9-2018 at 01:34

The easiest way of preparing a crude solution of cupric (copper II) tartrate is to use the old technique used by ancient alchemists in order to clean copper coins.
First boil a concentrated solution (verging on a suspension) of Cream of Tartar (Potassium Tartrate) and then throw in a load of old copper coins whose surface will be coated with a variety of impurities (these are of minor significance) including cupric oxide which will rapidly be dissolved into aqueous solution as a copper (II)-tartrate complex. As time goes by you will observe a) the surface of the coins becoming visibly cleaner and shiny and eventually the solution will turn to a pale blue-green colour demonstrating the presence of copper (II) hexa-aqua complex ions and one assumes in some sort of association with tartrate.
This is a good method for a quick result normally within 30 minutes as it avoids the use of using copper (II) sulphate that however lovely Blue Vitriol is, it tends to mask the colour of the tartrate that is less soluble than the sulphate, hence boiling the coins in an old Teflon coated plan. Copper coins also substitute for normal cupric oxide that can be difficult to find and purchase in some countries.

fusso - 13-9-2018 at 04:47

Quote: Originally posted by Dr Corvin Ravenden

The easiest way of preparing a crude solution of cupric (copper II) tartrate is to use the old technique used by ancient alchemists in order to clean copper coins.
First boil a concentrated solution (verging on a suspension) of Cream of Tartar (Potassium Tartrate) and then throw in a load of old copper coins whose surface will be coated with a variety of impurities (these are of minor significance) including cupric oxide which will rapidly be dissolved into aqueous solution as a copper (II)-tartrate complex. As time goes by you will observe a) the surface of the coins becoming visibly cleaner and shiny and eventually the solution will turn to a pale blue-green colour demonstrating the presence of copper (II) hexa-aqua complex ions and one assumes in some sort of association with tartrate.
This is a good method for a quick result normally within 30 minutes as it avoids the use of using copper (II) sulphate that however lovely Blue Vitriol is, it tends to mask the colour of the tartrate that is less soluble than the sulphate, hence boiling the coins in an old Teflon coated plan. Copper coins also substitute for normal cupric oxide that can be difficult to find and purchase in some countries.

What kind of countries would CuO be difficult to find? I don't think CuO could be used to make any drugs or explosives.

Jackson - 13-9-2018 at 10:21

nlegaux, you said you added IPA to the solution which cause a precipitate. Did the IPA cause the precipitation? Does IPA precipitate all copper salts?

DraconicAcid - 13-9-2018 at 12:37

Quote: Originally posted by Jackson

nlegaux, you said you added IPA to the solution which cause a precipitate. Did the IPA cause the precipitation? Does IPA precipitate all copper salts?

Adding an alcohol to an aqueous solution will reduce the solubility of all ionic compounds.

Lion850 - 11-7-2020 at 23:02

I recently acquired a bottle of old ammonium tartrate. Photo below. The lid was broken, but the contents was dry and looks like small glittering crystals - it reminded me of sugar. It did not have any ammonia smell which surprised me but adding a bit to a strong sodium hydroxide solution produces lots of ammonia gas so it seemed good. It was transferred to a different jar and I decided to have a go at making copper tartrate by double displacement:

(NH4)2C4H4O6 + CuSO4 = C4H4CuO6 + (NH4)2SO4

- 20g of copper sulphate pentahydrate was dissolved in 110g water in a beaker; it was heated to near boiling speed up the dissolving.
- 16g of ammonium tartrate was dissolved in 50g water; also heated to get a clear solution. This should have put the ammonium tartrate in slight excess.
- Solutions were mixed while still warm and hand-stirred for 10 minutes.
- Result was a pale blue ppt with a darker blue supernatant liquid. See photo. I wondered if the blue supernatant liquid was due to unreacted copper sulphate, and to check I decanted off the blue liquid and mixed it with more ammonium tartrate: there was no color change and no ppt showing that there was most likely no copper sulphate left.
- The contents was vacuum filtered and the light blue remainder dried on a steam bath until the weight stopped dropping. The drying did not change the color. See photo of the final product in the vial.
- Final dry product was 15.6g.

I found a few photos online of copper tartrate and it is the same color.

Why was the supernatant liquid blue after the double displacement? Online some sites says copper tartrate is very slightly soluble in water, which may be the reason. Or did the slight excess ammoinium tartrate form a soluble complex with a bit of the copper? I'll shake some up with water when next in the shed to see if it makes a blue solution.