anhydrous CrCl3

IrC, that looks like a not too hard to perform method, however....

I would want to build a tube furnace, but I dont have the time, room and money for it. Besides, I have never needed it before, and I'm not wanting to waste time, room and money, for the synthesis of a single compound.

But I appreciate the advice on how to build one greatly !
When I want to build one sometime, I know how!

Panziandi, I don't have toluene. Besides, phosgene may be useful, but it is simply not fun to play with, too toxic. I tend to avoid the gasses AsH3, H2Se and COCl2 at all cost unless milligram amounts are evolved.

Here is pontentially useful method of producing anhydrous metal chlorides from metal oxides. Dichloro Disulfane is extremly easy to make and the procedure could possibly be adapted to hydrated metal chlorides. Petrolium ether may work as a replacement for the carbon disulfide extraction of the final product.
Procedure for producing vanadium (III) chloride from vanadium pentoxide. Copied from the Hand Book of preparative Inorganic Chemistry; available in the Sciencemadness library.
2V2O5 + 6S2C12 = 4VCL, + 5SO2 + 7S
Fine, pure V2O5 powder (18 g.) and 40 ml. of S2Cl2 are refluxed
under anhydrous conditions for 8 hours (constant stirring). The
excess S2C12, containing dissolved S, is decanted and the VC13
formed is washed with dry CS2 . Adhering volatiles are removed by
heating the material at 120-150°C under vacuum or by extracting
it for several hours with CS2 in a Soxhlet apparatus. After thorough
purification, the residual sulfur content of the resulting fine crystals
of VC13 is about 0.2%. The yield is about 30 g.
Coarse (and hence less hygroscopic) crystals of VC13 are
obtained by heating the fine crystalline product with a small amount
of fresh S2C12 in a sealed tube at 240°C. Since no gas is evolved
in this operation, large amounts can be treated at one time.
The same reaction can also be carried out in a sealed tube at
300°C; however, smaller quantities must be used in this case (6-7 g.
of V205 and 20 ml. of S2C12).




[Edited on 29-1-2009 by benzylchloride1]

A few questions. First I will explain what I am going to do.

Im going to prepare some hydrated CrCl3 soon.
This will be done by heating a solution of potassium (or sodium) dichromate in concentrated hydrochloric acid (chlorine evolves). My first idea was using ethanol or methanol as the reducer, but I'm afraid acetate/formate will form a complex with chromium(III). Next I will evaporate ALMOST to dryness (to prevent hydrolysis) and let crystallise.
After filtering, I should have a 1:1 mixture of CrCl3.6H2O and KCl.

Next, I will add ethanol to solvate the chromium(III)chloride. NaCl and KCl are both 'slightly' soluble in ethanol. Wich one is the least soluble? I find data like 'slightly soluble' , but I have not find yet exact data. This will determine if I use Na of K dichromate.

After the extraction of CrCl3.6H2O with ethanol, and filtering, I will evaporate the ethanol. Problem is, will i just get the hydrated chromium chloride, or will I get chromium chloride with one or more ethanol ligands? If yes, would, after evaporating ethanol, adding some water and evaporating again replace all ethanol ligands with water ligands?

I have also been thinking about CrO3, but I only have 25g of this (donation from woelen ), and it is also nasty stuff to handle.

I will then try heating the hydrated salt with ammonium chloride, and after sufficient CrCl3 anhydrous has formed, i will add water to solvate all other materials (CrCl3 is insoluble in water, in the abscence of Cr(II) ).

Otherwise, maybe heating with acetyl chloride will help instead of heating with thionyl chloride. Or can't the water ligands be removed by acetyl chlordie on reflux?
I guess the acetic acid can't form a complex with the chromium? i think you need acetate for that, wich will not form in conditions where there is no water, just acetyl chloride.
And even if some will form, it can later be extracted from the purple anhydrous CrCl3, leaving CrCl3 behind (unless my flask is contamined with a very small piece of zinc ).

EDIT: I just found out dichromate oxidises Cl(-) in very acidic environment only very slowly. I added 1mL of sodium dichromate solution to 1ml of 37% HCl, and after boiling for 1 minute, the solution is dirty brown (a mixture of dichromate and Cr(III) ). So i have to find another reductor now, wich will still give me CrCl3.6H2O as product. I could also start from chromium aluim, but I rather don't as I only have 30 grams or so, and I would have to do it in 2 steps:
-precitipate hydrated Cr2O3 with dilute ammonia
-dissolve in concentrated HCl
Any ideas?

[Edited on 4-4-2009 by Jor]

I am now indeed seriously considering buying some Cr-metal. I can also use it to make some Cr(II) in solution and who knows what more.

Thank you very much for performing the experiment woelen!
Strange, I have seen a reference about the route, although I cannot remember where I have seen it. The 2 routes in Vogel are Cr reaction with Cl2 and Cr2O3 rxn with CCl4. Both use very high temperatures.
I have thought about reacting chlorine with chromium at lower temperatures I can reach with my burner, and although I think it will react albeit very slowly, it will be impossible AFAIK to remove the unreacted chromium metal from the anydrous CrCl3. For example, adding hydrochloric acid will produce Cr(II) and CrCl3 will quickly dissolve.

Very interesting about the reaction with PCl5 though. Maybe it will be possible to heat to the melting point of PCl5 to liquify it, and then, all POCl3 is instantly boiled away. Then, PCl5 is either evaporated as well, or one could destroy it by slowly adding water, and washing out the phosphoric acid by several washes with water, followed by drying at high temperatures (200C). I think none Cr(II) will be present, I don't see where it should come from, so no anhydrous CrCl3 should dissolve.
After all Brauer washes the CrCl3 with boiling HCl is both procedures.

Or does PCl5 sublime before it melts? If so, maybe a solution of the stuff in CCl4 can be refluxed with Cr2O3 (active Cr2O3, this can be ontained by decomposing ammonium dichromate), followed by distillation of the CCl4, and evaporating/subliming the PCl5, followed by washes with water. This way you don't have a solid-solid reaction.

I haven't made any PCl5 yet. Can you maybe perform the first or 2nd experiment on a test-tube scale woelen, look if it is possible to get pure CrCl3 from these methods? I'm not sure if they work, I just made them up myself.

I'm not sure, if you get those very nice crystals by these methods. Maybe the stuff should be sublimed.

------------------------------------

I indeed have plenty of sulfite and dichromate, but it seems like a lot of hassle for CrCl3.6H2O. I rather leave from Cr-metal, I will buy it soon I think.

[Edited on 8-4-2009 by Jor]

Wow, you refluxed with thionylchloride for 2 days ? That's a very long time. Now I understand why I did not see anything interesting happen. I stopped after half an hour or so. How do assure safety with such long-lasting refluxes? I never let any active system (reflux, distillation, heating bath, heating mantle, etc.) run unattended, so for me, such refluxes for such a long time are no option at all.

The CrCl3.6H2O I used is somewhat wet, it is made from Cr-metal and conc. HCl, which works quite well, at least if you allow the liquid with the metal pieces to stand for a long time (having such tame liquids standing and brewing for a long time is no problem for me). I usually do the drying on a heat radiator, with a paper tissue loosely covering the beaker, such that no dust gets in the crystals. In this way, I made a lot of metal salts, like NiSO4.6H2O, Co(NO3)2.xH2O, Cu(HCOO)2.xH2O, CrCl3.6H2O, PrCl3.xH2O, and many more.

The wetness of the CrCl3.6H2O quickly reacts with the thionyl chloride, but the water molecules which really are part of the hydrate do not react, at least not quickly. I also find it quite unusual that an inorganic chemistry reaction is going so slowly. Probably this is unique for chromium(III), because the water-ligands are attached to chromium(III) very firmly. Complexes of chromium(III) and cobalt(III) are rather inert and ligand-exchange or ligand-removal is very slow.

Ok, I finally made some CrCl3, although it is not yet pure.
I first dissolved some chromium metal in concentrated hydrochloric acid, blew some air through it, and evaporated to dryness. The crystals were not that hygroscopic it seems.

A test-tube was placed almost horizontally, and 0,5mL of CCl4 was placed in the bottom of the test tube. Next in the middle CrCl3.6H2O crystals were placed. The crystals were heated with a small propane flame, and with the same burner I heated the CCl4 for short intervals such that it boiled slowly. The volume expanded, and I could see the purple color, but the conversion was far from complete. I decided change my plan somewhat. I heated the entire test tube more strongly (still pretty small flame, the reaction does't require high temperatures). Next I pippetted some CCl4 and brought the pipette as far in the test tube as possible and spewed it , such that it would reach as far to the bottom of the test tube as possible. The CCl4 instantly evaporated. After repeating a few times I collected my solid. It was a purple powder, but still contaminated with a small amount of green material. I attempted to dissolve theis with boiling 2M HCl, but it did not work. The CrCl3 did also not dissolve, wich is nice, as it shows no CrCl2 is present. Adding zinc dissolved the purple materials in less than a minute.

So I did the same procedure described above once more, and tried something else: putting the test tube vertically and heating the CrCl3 at the bottom, and next dropping CCl4 (I used up 1mL CCl4 in this step) on the solid.

After these treatments the solid was less contaminated, but still green residues remained. It is a waste of CCl4 to remove the last traces (I used up like 5mL today in trying many of these things). I think the solid is at least 90-95% CrCl3.
I will make some more batches (I don't have to glasware to work on a larger scale, as for larger scale you need a long tube, where I could lead in CCl4 vapour on one side and absorb the phosgene on the other side (ground glass joints).

When I have enough crude material, I will attempt to make the beautiful purple metallisch crystals, by subliming in a stream of Cl2.

Slowly heating the hydrated chloride alone gave a purple solid, but it decomposed on further heating, so it was probably [Cr(H2O)6]Cl3. The green hydrate is [Cr(H2O)4Cl2]Cl.2H2O .

Is it possible to extract the CrCl3 with a solvent? Maybe ether? CrCl3 is a pretty strong Lewis acid IIRC, and it should form an adduct with ether right? If yes, would it be possible to decompose the adduct by heating?

I am happy I will get 250mL CCl4 in a week, as I only have a small amount left (maybe 20mL).

[Edited on 4-6-2009 by Jor]

I found an article regarding the tetrahydrofuranate (didnt realise benzylchloride1 had already mentioned it ) that I thought I would share. It'll give you something nice to do with your anhydrous CrCl3, and will also enable you to make organometallic complexes (as the article suggests). Now, in my honest oppinion I find complex chemistry quite boring, but to see some triphenylchromium complex... well that might just convert me

Attachment: Chromium trichloride tetrahydrofuranate.pdf (142kB)
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Ah...thanks for the correction. I should have caught that Cr+3 wouldn't be much of an oxidizer.