Sciencemadness Discussion Board - Making Gold III chloride?

Making Gold III chloride?

rolynd - 30-12-2005 at 05:36

I need some Goldchloride for colouring purpose.
Buying seems too expensive. So I opted for making some myself.
My initial thoughts were to use a Gold Anode with HCL solution and apply some current. Goldchloride should easily form.
Is this practical? are there any significant amounts of other unwanted chemicals produced? See any problems here?
Or should I opt for the more traditional approach using Aqua Regia dissolving some gold first then forming the salt later.
Any Ideas on this? I would want to use some 18k Gold Alloy for this.
Regards
Rolynd

BromicAcid - 30-12-2005 at 10:07

Depending on the current you run through the electrode some perchloric acid may form although electrolysis is not a good way to form perchloric acid so I don't think much perchlorate would form. Still you're going to be making a lot of nasty fumes, mists of HCl and some chlorine gas, but I would think it would dissolve forming the chloroauric acid. But I have no practical experience in this area so it's all speculation, I know fleetingly little about the properties of gold as an anode.

Of course the traditional approach likely gives better results considering it is the traditional approach, in addition you'll be able to find more of the important details to carry out the procedure. If you have nitric acid then maybe you should consider the traditional approach.

Finally, you realize that your gold alloy is going to carry with it a number of impurites aside from gold. At 18K only 75% of the alloy is gold, the remainder being silver and copper, the silver should precipitate out as the chloride but separating the copper may be more difficult.

chloric1 - 30-12-2005 at 11:37

If nitric acid is not readily available Sodium nitrate might work. Warm HCl then add sufficient sodium nitrate. Sodium chloride should precipitate so you should filter this through diatamacious earth or other inert material before putting the gold in. I have also read solutions of free halogens attack gold. So potassium bromate mixed with bromide? A triiodide solution?

rolynd - 30-12-2005 at 17:20

Thank you very much. So, no easy approach. Some nitric acid is at hand so I will try the traditional one and check for some more info first. Instead of the 18k alloy It seems more practical to obtain one or two of the smaller maple leaf or krugerrand coins which have .999 purity. What I am needing to make is something called "Cassius'scher Goldpurpur" ,a radiant purple colored pigment, heatesistant, used for coloring rubyglass and jewelry in enameling. Some Iod would also be avaliable but this is nothing for the workshop I think.

Fleaker - 30-12-2005 at 19:26

I suggest you melt the gold with excess copper to drop the karatage to 8 or below then digest it all in nitric acid when cool. This will leave a residue of pure gold and any platinum that remains while the copper and any silver or palladium will be dissolved in the nitric acid. Then add 1 part nitric to 3.5 parts hydrochloric and the brown-black gold powder will dissolve. After all is dissolved (any residues would be platinum or a congener, the former is insoluble at room temperature aqua regia) you will then boil it down to a syrup to expel any nitric acid present which will go off as NOx, then add more HCl and repeat about 2-3 more times finally reducing it down to a thick brightly coloured syrup. Let this dry out and you should be left with crystals of pure AuCl3, have caution with the syrup though, it will stain your hands black!

[Edited on 31-12-2005 by Fleaker]

rolynd - 3-1-2006 at 09:35

I have done some research on this and some new questions did arise.
So far the Procedure is:
- make some 6k alloy by melting the 18k with the proper amount copper
- dissolve this in nitric acid ,22-23k gold should remain undissolved
- Preparing some aqua regia and dissolve the 23k gold
- Distilling the acid down to almost solid
-adding HCL and distill some more
-repeat the last step a few times to get rid of the remaining nitric acid
As I am not working in a fully equipped lab and usually work with more diluted acids I am concerned with the NOCL and NOx fumes which are generated by the distilling.
As I dont want to keep the fumes can I get rid of those by working with a closed system attaching a hydroaspirator to the flask and just sucking the nasty fumes down the drain? Would this work or should the fumes be fitrered through some water or other neutralizing agent first before finally sucking them down the drain? Is the usual hydroaspirator able to deal with the amount of fumes generated?

mick - 3-1-2006 at 11:12

Have you thought of sign writers gold leaf as the source of gold. I am not sure of the grades available but I think it has to be fairly pure to be so thin/malleable. Being wafer thin it might be easier to clean and dissolve/react??
Depends on the amount of pigment required.

mick

rolynd - 3-1-2006 at 12:53

Have thought of this myself but the price would be more than the other variant. I could also go an get some .999 fine gold sheet or casting grain or some of these fine gold bars or coins but these will have to be bought.

On the other side I have some 18k alloy sheet at hand I could use with proper preparation (small amount melting and pouring is done regularly, so I have experience with this) What I am not used to are the strong acids used. For etching I use much more diluted ones. So almost all the needed material like the gold, the acids, hydroaspirator are avaliable with no further cost.
Right now I am working on the problem with the noxious fumes. The idea of just sucking them down the drain sounded good to me. Just dont know yet if its practical.
I am needing about 5grams of Goldchloride. At about 95€ per gram buying this would be a little expensive...
While studying (biology) I had to make two big practical courses one in organic chemistry the other in anorganics doing lab experiments. each lasting several weeks so I am not without practical knowledge but things like this we never did there...
Also I do not know all the proper english words for chemicals and lab stuff but it seems you understand what I want. Thanks

mick - 3-1-2006 at 13:34

If you have thought of all the other options, best of luck if you want to do what you are going to do.

mick

neutrino - 3-1-2006 at 14:33

An aspirator should easily handle this, assuming the vapors are soluble in water. You don’t really want a vacuum aspirator, however. What you want is something similar, I’m not sure of the name. Look in some chemistry textbooks and you should find it.

My suggestion is to just boil it outside or in a fumehood and not worry about the fumes. In these amounts, you shouldn’t have much excess to worry about. If you don’t want to do that, you can bubble the vapors into a solution of lye (NaOH, available in any store as drain cleaner in one form or another). This should clean the NOCl and HCl out of the vapor. Just be careful about suck back when the solution stops boiling.

Fleaker - 3-1-2006 at 15:43

The vapors will destroy the hosing, trust me. Aqua regia's fumes quickly rust steel (even some stainless) and neoprene rubber used in tubing is affected, let me assure you. You're best bet is to do it outside or any place were you have adequate ventilation and nothing metal that you don't want oxidized. You might try an NaOH trap such as that suggested by neutrino, and yes, do avoid suck back (a bad thing if the flask is really hot), to avoid it, just set up 3 bottles in parallel. Then again, you could just do it outside!

Follow the procedure I outlined for that 18K gold and you'll be fine, I've done it before and I know it works. You can figure out how much nitric you need to react with the copper you inquartated the gold with through simple stoichiometry, then double the volume to account for the silver and the decomposition of the acid. Rinse the brown powder with distilled water, then nitric acid, and again with warm distilled water (till there is no blue/green coloration). A buchner funnel would be helpful there as vacuum assist makes it go quicker. Then you would digest in aqua regia and separate any platinum out by decanting or filtration onto fritted glass (hot aqua regia will clean the residue off).

Personally, I suggest you buy some 1g bars of Au , not a coin since they cost more because there is also the numismatic value of the coin. These 1 g bars can be wrapped up in cloth and placed on a hard surface (anvil is ideal) and struck until well flattened; these homebrew 'cornets' will dissolve quickly in 20C aqua regia. Finally, as I mentioned, just boil it down and then crystallize.

[Edited on 3-1-2006 by Fleaker]

oneup - 4-1-2006 at 04:23

Gold won't dissolve in nitric acid. you need to make a mixture of 1 part nitric acid and 3 parts hydrochloric. that will dissolve gold, forming gold chloride.
you might be able to purify the gold by putting it in nitric acid, the copper that's in the gold will dissolve while pure gold will not dissolve.

to dissolve gold.

Ephoton - 6-1-2006 at 04:12

to disolve gold one needs a reaction that oxidizes the golds
surface and a reaction that turns the oxide into a halide acid
(cyanide and salt fusion exept).
gold chloride and chloroauric acid are two different things.
I disolve a lot of gold and im starting to get into plat group.
trust me NO2 is a real bitch so if you find a way that works
that doesnt use a nitrate source then go for it.
I have heard of people using perchlorate as the oxidizing
agent and even insitu generation of this from salt solution
via electrolasis.
I am thinking of changing from aqua to making perchlorate
first then mixing with hcl I think it would be much nicer
and aparently from a few sites I found from google it disolves
rhodium cold.

woelen - 6-1-2006 at 10:23

I have done experiments with the perchlorate/HCl mix, but this is not much different from HCl alone. Perchlorate, even up to 60%, mixed with chloride does not form any chlorine. I have even tried heating the liquid a lot (over 100 C I'm quite sure), but even then there only is a very faint smell of Cl2 right above the test tube (the average municipal swimming pool has a stronger smell). I also did such an experiment with 60% HClO4 and KI. No formation of iodine at all. Only after long standing the liquid turned light yellow, probably because of oxidation of the iodide by oxidation by oxygen from the air. Even heating to around 80C did not give an appreciable reaction.

So, if you want to dissolve gold with the help of perchloric acid, then you'll need acid of very high concentration (at least 72%, but probably a little more) and some heating. HClO4 is not oxidizing at lower than appr. 70% concentration. The reason for this is not it being a weak oxidizer from a thermodynamic point of view, but apparently the activation energy for the breakdown of the perchlorate ion is very high, when water is present. So, it is more like a kinetic problem with no suitable pathway for the reaction to proceed.

You might have more succes by mixing NaClO3 with HCl and adding gold metal. Do this reaction, however, outside or in a good fume hood, because of formation of Cl2 gas and also ClO2 gas. The latter is less toxic, but it is really explosive. So, assure that no buildup of this gas can occur in a confined space.

12AX7 - 6-1-2006 at 10:40

Quote:

Originally posted by woelen
You might have more succes by mixing NaClO3 with HCl and adding gold metal. Do this reaction, however, outside or in a good fume hood, because of formation of Cl2 gas and also ClO2 gas. The latter is less toxic, but it is really explosive. So, assure that no buildup of this gas can occur in a confined space.

I thought ClO2 was worse? Smells worse at any rate...(just like any other oxidizing gas, but with this horrible choking flavor thrown in!).

Tim

Fleaker - 6-1-2006 at 16:30

Well the ClO2 doesn't form in enough quantity to explode (IIRC according to "General Chemistry", 3rd Edition, Linus Pauling, it has never been isolated, at least at the publishing) but it is odorous. I see ABSOLUTELY no reason to use perchlorate ion when aqua regia works just fine, nor do I see any reason for repeatedly posting the aqua regia method:

Oneup said:
"Gold won't dissolve in nitric acid. you need to make a mixture of 1 part nitric acid and 3 parts hydrochloric. that will dissolve gold, forming gold chloride. you might be able to purify the gold by putting it in nitric acid, the copper that's in the gold will dissolve while pure gold will not dissolve."

I believe I mentioned that further up the thread.

I do find Ephoton's mentioning of HClO4/HCl mixture that dissolves rhodium interesting, but I do not know how useful it would be when sulfuric acid and halide salts can accomplish the same thing. (Ref. USPTO: 5542957U) Perchloric acid is expensive, and not as readily obtained in concentration as say sulfuric or nitric acids, both of which are very cheap.

[Edited on 7-1-2006 by Fleaker]

insitu

Ephoton - 7-1-2006 at 00:40

there are quite a few salts on the market that I belive are
oxidized halide salts. the idea behind a few of them is you
dont use acid at all you place salt in water then apply a voltage to crack salt and make oxidizing halid acid.
they do it this way in quite a few countrys where it is
hard to get permission to use aqua in large volume.
I would in any varity disolve gold forget nutralizing oxadizing
agent. make basic to drop hydroxide mud. disolve hydroxide mud in hcl to make chloride salt.
this of course will only work with pure gold not alloyed
or electronics.

reagents are local

Ephoton - 7-1-2006 at 00:46

reagent aquasition is a locality thing not every one can
get nitric. yes I have it but It was a long and hard strugle
to get it and I am always scared of using too much as I
dont know if I can get more.
sulfuric and halide salt hmmm this is very thankfully taken on
board
and trust me once you start trying to work any kind of volume
of the nobles you as do I will regret choosing a nitrate route.
if its a once off get some pure gold a glass hcl nitrate fert
do it out doors. once no more red/brown smoke comes off
it make basic ect ...

mick - 7-1-2006 at 15:46

I might be wrong but I thought that

Aqua Regia dissolves gold because the conc. nitric acid converts the conc. hydrochoric acid into a very strong oxidiser.

mick

neutrino - 7-1-2006 at 19:37

The route of action of aqua regia is not so complicated. First, the metal is oxidized by a strong oxidizer in the solution (Cl2 and / or NOCl if memory serves). The metal ions are then forced into solution through the complexing ability of the chloride ion. In the example of gold, the AuCl4- ion is produced.

I wonder if there are any other good oxidizers that will do the job.

I know that fenton's reagent is one of the strongest oxidizing solutions known, I wonder if that will do the job with a little NaCl thrown in. This must be tried.

edit: Just tried it with gold leaf and it seems to work. It dissolved slowly at room temperature, but the leaf is gone. It is possible, however, that the leaf only curled into a very small and invisible ball (it is extremely thin, after all). I will repeat it tomorrow and do a test for gold ions.

[Edited on 8-1-2006 by neutrino]

woelen - 8-1-2006 at 12:18

Quote:

Neutrino
edit: Just tried it with gold leaf and it seems to work. It dissolved slowly at room temperature, but the leaf is gone. It is possible, however, that the leaf only curled into a very small and invisible ball (it is extremely thin, after all). I will repeat it tomorrow and do a test for gold ions.

You can recognize easily if gold dissolves. The liquid obtains a really distinct golden/yellow color, which is quite strong. This is the color of the AuCl4(-) ion.

Quote:

Fleaker
Well the ClO2 doesn't form in enough quantity to explode (IIRC according to "General Chemistry", 3rd Edition, Linus Pauling, it has never been isolated, at least at the publishing) but it is odorous.

I think you are confusing this with another oxide. ClO2 is very easy to isolate (but dangerous). I have made this gas many times. It is an increadibly intensely colored gas. A picture of some (impure) ClO2 I made is given here:

http://woelen.scheikunde.net/science/chem/exps/clo2/index.ht...

It can be made in a 1 : 1 ratio with CO2 without chlorine by mixing KClO3, (COOH)2 and H2SO4, but I never dared doing that, being afraid of a possible explosion.

The gas is isolated, however, many times and I have (old German) books, which contain recipes for the making of this gas in pure form.

[Edited on 8-1-06 by woelen]

Fleaker - 8-1-2006 at 17:25

I do not think I am confusing it with another oxide (although that is a definite possibility) but I believe you are making the hydrate of chlorine dioxide, not the pure substance itself. I seem to recall reading that it has never been isolated in that manner as it detonates. However, if you have books giving the recipie for making pure ClO2, then I must be mistaken.

I made a new discovery I think

Ephoton - 10-1-2006 at 15:01

well on the idea of a new oxidzer I went ahead and got
the first one I could lay my hands on

ammonium per sulfate.
I then added hcl and ti dissolved gold

no nasty gas either.
my mix isont perfect still needs work but it disolved some

and on alkali salts to fuck up drop a pgm sep

Ephoton - 10-1-2006 at 15:02

no alkali salts sorry not on

garage chemist - 10-1-2006 at 15:36

From the Article about Gold in Encyclopedia Britannica (a very good read!):

"Auric chloride, or gold trichloride, AuCl3, is a dark ruby-red or reddish brown, crystalline, deliquescent powder obtained by dissolving the metal in aqua regia. It is also obtained by carefully evaporating a solution of the metal in chlorine water. The gold chloride of commerce, which is used in
photography, is really a hydrochloride, chlorauric or aurichloric acid, HAuCl4.3HiO, and is obtained in
long yellow needles by crystallizing the acid solution."

So essentially you dissolve gold in aqua regia and evaporate the acid carefully.
Or you can dissolve gold in chlorine water (an interesting method!) and evaporate this to also get auric chloride.

[Edited on 10-1-2006 by garage chemist]

neutrino - 10-1-2006 at 15:44

I tested my solution and it came out negative. I think the flocculent precipitate at the bottom of the solution contains gold, I must check some solubilities to be sure.

nice one :)

Ephoton - 11-1-2006 at 00:30

I would disolve some of the precipitate then add tin
if you get a purple precipitate its got gold in it.
purple cassias.

Aqua Regia

AndersHoveland - 11-10-2011 at 14:47

The mix of concentrated nitric and hydrochloric acids in aqua regia exists in an equilibrium. The equilibrium only begins moving to the right when the acids are very concentrated. Even heating 30% conc HCl with NaNO3 will give off some brown fumes.

HNO3 + (3)HCl <==> (2)H2O + NOCl + Cl2

(2)NOCl + H2O --> NO + NO2 + (2)HCl[aq]

Aqueous solution of chlorine can attack gold.

(2)Au + (3)Cl2 + (2)Cl[-] --> (2)AuCl4[-]

An interesting way to reduce gold(III) chloride back to elemental gold is to use an alkaline solution of hydrogen peroxide. Although usually oxidizer, in some reactions H2O2 can act as a reducing agent.

(2)AuCl4[-] + (3)H2O2 + (6)OH[-] --> (2)Au + (8)Cl[-] + (6)H2O + (3)O2

The gold usually separates out in a finely divided state, and appears brown by reflected light and greenish blue by transmitted light. If very dilte solutions are used, the gold sometimes separates out forming a yellowish film on the sides of the test tube.

[Edited on 11-10-2011 by AndersHoveland]

BJ68 - 31-1-2017 at 23:52

Old Thread, but I obtained 20 g gold pellets and will sacrifice about 2 g for making Gold(III)chloride.

I found this article: "A Straightforward Route to Tetrachloroauric Acid from Gold Metal and Molecular Chlorine for Nanoparticle Synthesis" http://www.mdpi.com/2075-4701/5/3/1454/pdf and will use this method.

The only things what I will change is
a) the solution will be evaporated in a rotary evaporator under vacuum and not freeze dried to obtain Gold(III)chloride.
b) the volume of HCl (down to under 50 ml)
c) mass of gold (1-2g)

Problems what I see:

Changing the concentration of the produced Tetrachloroauric Acid can influence the stability of the solution....and the heating will be critical, too. Very clean flasks have to be used....

Opinions?

Bj68

[Edited on 1-2-2017 by BJ68]

nezza - 1-2-2017 at 01:35

The beauty of using Aqua Regia is that all of the products are volative or gases so the gold solution can be evaporated to leave pure aurichloric acid. Any other route leaves solid impurities which are difficult to remove without reducing the gold(III) back to metallic gold. Adding alkali to aurichloric acid does not generally precipitate any gold oxides but does make the solution incredibly sensitive to reduction to metallic gold. I appreciate that in some countries in the EUSSR it is impossible to buy nitric acid of any useable concentration now, but small amounts can be distilled from nitrates and phosphoric acid.

BJ68 - 1-2-2017 at 01:48

Hm....sorry but if you look at the paper: They use only hydrochloric acid and pure chlorine and nothing else. Hydrochloric acid is the main ingredient of Aqua Regia and chlorine is volatile.

So which advantage do I have if I use Aqua Regia? They only thing I think is the time advantage....with Aqua Regia it goes much faster, but so far what I have read you have to make sure, that all nitric acid is evaporated...that means you have to add hydrochloric acid and boil down the liquid a few times until no brownish vapors are visible.

Bj68

Sulaiman - 1-2-2017 at 01:53

I would go for the Aqua Regia (AR) route, (I found it surprising how fast gold 'dissolves')

add excess HCl to Au, heat, add HNO₃ until just a little gold is left,
this ensures that there is no excess nitric acid to be removed

the HCl boils off easily, leaving HAuCl₄ as pure as your starting components.
a simple one pot synthesis.

recover any precipitates (e.g. un-reacted, or precipitated gold) by decantation as filtering always results in mechanical losses.

EDIT: afterthought .. I have not recovered HAuCl₄ crystals this way, I jist meant that MOST of the HCl boills off easily, I did not try further.
but, when I tried direct 2Au + Cl₂ = AuCl I got more AuCl₃ than AuCl

[Edited on 1-2-2017 by Sulaiman]

[Edited on 1-2-2017 by Sulaiman]

BJ68 - 1-2-2017 at 03:30

Can check both routes....working at a University, so supply with reagents is not a problem...and if some thing goes wrong, I can recycle the "waste".

Bj68

j_sum1 - 1-2-2017 at 11:55

Dang it is frustrating how many experiment ideas that I have been mulling over for a while have resurfaced on the board when I am still sans lab.

Sulaiman presented some interesting stuff last year on the twelve keys of Basil Valentine and the making of AuCl3 appears to be key 3. This graphic shows his procedure. (The illustration was done by someone other than Valentine.)

Attachment: 03.Musaeum_Hermeticum_1678_p_398_III._Clavis_AQ27.tif (4.6MB)
This file has been downloaded 714 times

It is worth looking up Valentine's description of the procedure and also the modern interpretation of it. I can't lay my hands on it just at the moment. But the key to his process is the fighting roosters and fox in the midground. The fox is aqua regia (the only sneaky thing that can dissolve gold.) The rooster is the gold. The fox consumes the rooster. The rooster consumes the fox. Through evaporation the rooster is regenerated. A cycle of repetitions eventually gives a chlorinated atmosphere. And when it becomes anhydrous the fiery red crystals of dragon's blood appear.

AFAIK, auric chloride is very sensitive to water - deliquescent and so difficult to make and store. Also excessive heating drives off Cl2 leaving gold again.

I have devised a procedure that I intend to try later this year. Anhydrous conditions and reacting the gold directly with Cl2 and NO2. No idea how successful I will be but that is half the fun.