Dimethylglyoxime, H2DMG

Dimethylglyoxime H2DMG

Dimethylglyoxime, IUPAC name: 2,3-Butanedione Dioxime, Formula: C4H8N2O2 is a white cristalline solid, insoluble in water, but soluble in some organic solvents. The molecule has two acidic protons and thus dissolves in aqueous NaOH as a sodium salt. It is used in qualitative and quantitative determination of nickel and/or palladium:

Pd(II) + 2 H2DMG => Pd(HDMG)2 + 2 H+ yellow precipitate
Ni(II) + 2 H2DMG => Ni(HDMG)2 + 2 H+ intense red pecipitate

From acid solutions Pd can be precipitated in the presence of Ni selectively. Ni precipitates only from alkaline (ammoniacal) solution. In gravimetric determinations usually a 1% solution of H2DMG in alcohol is used. To precipitate Pd from acid solutions, especially if other precious metals are present, a solution of H2DMG in aqueous NaOH is preferred. Such a solution can be prepared by first dissolving 4.00 grams of NaOH in 100 ml of water, followed by dissolving 5.81 grams H2DMG in this 1M NaOH-solution.

To precipitate 1.00 g Pd 2.5 g H2DMG, corresponding to 43 ml of the above cited alkaline solution are necessary. In addition it has to be made sure, that the resulting mixture remaines acidic.

freechemist

DMG is quite expensive if one tries to buy it in the US, but there is a Russian source on Ebay that supplies a very good quality product at reasonable cost. I recently reordered some and it took less than 2 weeks for it to arrive.

http://cgi.ebay.com/Dimethylglyoxime-10-grams-Chugaevs-Reagent-/270707850780?pt=LH_DefaultDomain_0&hash=item3f0771fe1c

1-What is the simplest way to make DMG?.

2-Palladium being similar to silver...

What is the equivalent chemical to DMG that will scavenge selectively and quantitatively silver from solutions?. :shock: :?:

HAuCl4 said:

1-What is the simplest way to make DMG?.

2-Palladium being similar to silver...

What is the equivalent chemical to DMG that will scavenge selectively and quantitatively silver from solutions?. :shock: :?:

Click to expand...

Here ya' go:

http://en.wikipedia.org/wiki/Dimethylglyoxime

Irons said:

HAuCl4 said:

1-What is the simplest way to make DMG?.

2-Palladium being similar to silver...

What is the equivalent chemical to DMG that will scavenge selectively and quantitatively silver from solutions?. :shock: :?:

Click to expand...

Here ya' go:

http://en.wikipedia.org/wiki/Dimethylglyoxime

Click to expand...

I'm sure someone here can post the "cooking recipe", and I was hoping for that. :lol:

HAuCl4 said:

I'm sure someone here can post the "cooking recipe", and I was hoping for that. :lol:

Click to expand...

Take a look at a Merck Index.

Harold

I do not have access to that, but it sure looks like a very fine reference. Thanks Harold.

Orgsyn.org has a preparation of dimethylglyoxime. I had a look at it and considered making a large batch for sale here (I already have all the required chemicals), but after some number crunching I can't beat the price at that ebay link or from chemical suppliers.

The synthesis is not short, nor sweet and uses up a lot of sodium nitrite and metabisulfite.

If people are willing to pay me for the supplies and time, I will do it, however.

freechemist

Your formula for recovering palladium from a solution contains quite a bit of NaOH which might be troublesome for testing drop for drop (ph shift) for the presence of palladium.

Would a smaller amount of NaOH assist in the solubility of DMG without such a strongly alkaline solution?

LittleJohnnyH2SO4 said:

Orgsyn.org has a preparation of dimethylglyoxime. I had a look at it and considered making a large batch for sale here (I already have all the required chemicals), but after some number crunching I can't beat the price at that ebay link or from chemical suppliers.

The synthesis is not short, nor sweet and uses up a lot of sodium nitrite and metabisulfite.

If people are willing to pay me for the supplies and time, I will do it, however.

Click to expand...

I was looking for the recipe to see if I could make it myself. Cheers.

HAuCl4 said:

LittleJohnnyH2SO4 said:

Orgsyn.org has a preparation of dimethylglyoxime. I had a look at it and considered making a large batch for sale here (I already have all the required chemicals), but after some number crunching I can't beat the price at that ebay link or from chemical suppliers.

The synthesis is not short, nor sweet and uses up a lot of sodium nitrite and metabisulfite.

If people are willing to pay me for the supplies and time, I will do it, however.

Click to expand...

I was looking for the recipe to see if I could make it myself. Cheers.

Click to expand...

A google search would have turned it up. orgsyn.org is free to everyone: http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv2p0204

Cheers Johnny. 8)

qst42know

Solutions of PdCl2 in diluted HCl usually contain an excess of acid, so pH-shifting on addition of the alkaline DMG-solution should not be a problem. If you want to be sure, that the Pd-solution to be treated with DMG, remaines acidic after addition of DMG, you can add a small quantity of 1M HCl before addition of the alkaline DMG-solution. For every gram of Pd to be precipitated, about 22 ml of 1M HCl are sufficient.

freechemist

I believe that DMG is not completely selective for Pd if there is silver present in nitrate solutions, or gold present in chloride solutions. I imagine temperature plays a big role too, but I do not have any charts to back it up. :roll:

HAuCl4

As far as I have experienced it in practice, silver has never been a problem in palladium precipitation out of nitrate solutions. In the production of 999.9%o pure silver by electrolysis one of the most critical impurities is Pd, dissolved in the AgNO3-electrolyte. If it's concentration becomes much higher than about 50 mg Pd/l, it will begin to deposit at the cathode in significant amounts. This can be avoided by precipitation of Pd as Pd(HDMG)2 and circulating the electrolyte through filtering torches, which hold back the Pd-precipitate.

Gold(III) in acidic chloride solution - if it is not reduced by DMG - will probably form a complex cation [Au(HDMG)2]+, which will not be precipitated
and stay in solution.

freechemist

Thanks freechemist.

What you posted complements my observations. Although all the palladium was scavenged from the solutions (quantitatively), the DMG precipitate was contaminated with silver (nitrate solutions) and gold (chloride solutions), so DMG wasn't 100% selective for Pd when silver or gold are in solution with Pd. The colder the solution the less contamination of the palladium-DMG precipitate in both cases.