Sciencemadness Discussion Board - Making of antimony pentachloride

Making of antimony pentachloride

RU_KLO - 2-8-2025 at 17:25

I need some antimony pentachloride. (not much, from 500 mg antimony metal)

from Handbook of Inorganic Chemicals
Pradyot Patnaik, Ph.D

by the reaction of the element with excess chlorine:
2 Sb + 5 Cl2 → 2 SbCl5

and also from SM wiki:

Antimony(III) chloride can be prepared by reacting elemental antimony with dry chlorine gas. Reaction must be performed in dry environment/atmosphere

So, my idea was to make a train consisting of:

1) chlorine generator (isocyanuric acid + HCl)
2) CaCl2 as drying agent
3) test tube with filed antimony metal. (bellow will be an alcohol burner to heat the antimony dust)
4) NaOH scrubber
5) sucking pump

Also I will make a 6M HCl saturated with chlorine. (I dont have fumming HCl, the best I can get is azeotropic 20% HCl)

I will put the antimony "tri/penta" chloride produced in the test tube into the HCl + Cl2 solution.

Do you think I could get the pentachloride this way?

Is heating dangerous (explosion?) or it is not necesary? (I think that heated antimony metal reacts with chlorine faster and better than cold, but never performed a chlorination with Cl2 gas + metal)

I "know (read)" that tri/penta(more) is hydrolized very easy.

I already dissolved antimony metal (filed dust) in 20% HCl without problem.

I will test if any pentachloride with KI. (this is the qualitative test to differentiate penta from trichloride antimony.)

What are your thoughts? (I know chlorine dangers, it will be perfomed outside (+ NaOH scrubber) and small quantity.

charley1957 - 3-8-2025 at 04:52

I’ve been investigating this lately, and I find that this reaction needs to be done at 300 degrees C. The resulting liquid then needs to be distilled under chlorine gas. I need more information before I try it, and I’ll have to look this up again, but I’ll do that and present my sources and findings here or I can U2U you with it.

bnull - 3-8-2025 at 09:21

@charley1957: Are you sure? The temperature you indicate seems too high. Antimony trichloride boils at ~230 °C and the pentachloride at 68 °C.

Brauer (pp.608-611, attached below) has a few procedures to prepare tri- and pentachloride. Trichloride can be made by passing dry chlorine over pieces of antimony and applying heat only at the end, and pentachloride by passing chlorine on molten antimony trichloride. Both look pretty straightforward to do in the scale you want.

Is it by any chance related to the orpiment oxidation experiments?

Attachment: antimony chlorides.pdf (196kB)
This file has been downloaded 97 times

[Edited on 3-8-2025 by bnull]

teodor - 3-8-2025 at 13:58

The preparative method using the dry chlorine is very complex. If you would like to search the forum you find there is no report of successful synthesis here. Extremely corrosiveness, water sensitivity and volatility of SbCl5 could be also the reason nobody found a way to deal with the synthesis.
To exclude some complexities like gaseous reagents and drying you could try a chlorosulfonic acid + antimony method of getting SbCl3 modifying it with some additional decomposition of the acid to make it Cl2 source at the same time.

[Edited on 3-8-2025 by teodor]

charley1957 - 3-8-2025 at 18:24

I’m going by the a video on YouTube on a channel called Edward Tries. He makes antimony pentachloride and has his flask heated to 300C. I haven’t looked at other preparations yet.

woelen - 3-8-2025 at 23:42

Theoretically, the synthesis of antimony chlorides is not hard. Just passing chlorine over antimony.

The devil is in the practical details. The chlorine must be perfectly dry and it must be passed over the antimony very slowly. I have seen a synthesis, which uses a special piece of glassware, a kind of tube, which is bent over a not too big angle (10 degrees or so) and which is made wide in the middle. Shiny pieces of 5 mm to 1 cm without oxide layer of antimony are put in this tube, several cm before the end of the tube. The bulb (wide part) is somewhat lower. When the chlorine slowly passes over the antimony, then it forms trichloride and pentachloride. This mix liquefies and slowly runs into the bulb (hence the small angle of 10 to 15 degrees). The angle must be such, that the pieces of antimony do not slide down the tube, only the liquid should run down the tube. In the bulb, there is excess chlorine over the impure SbCl5. Any SbCl3 then reacts further with Cl2.

At the end of the tube, a flexible tube must be connected, which is not open to air, but goes through a drying column with CaCl2/P4O10 mix. Finally, the outlet must be put in a fume hood. Excess Cl2 is blown off.

This apparatus requires a very constant slow flow of Cl2. It must be possible to easily insert new pieces of Sb when the Sb is used up. It also is very important that no pieces of Sb slide into the liquid in the bulb, otherwise you get severe contamination with SbCl3.

When all is done, then the liquid must be transferred to a distilling flask, meticulously avoiding entrance of any air (water vapor!). Then the material needs to be distilled to purify it. I'm not sure whether this distillation can be done normally, or uses vacuum. SbCl5 should not be heated too strongly, otherwise it decomposes to SbCl3 and Cl2.

In practice, this setup is very hard to make and maintain operational. Getting a nice constant and slow flow of perfectly dry Cl2 for an extended period of time can hardly be done without a bottle of pressurized chlorine gas, with a precision regulator on it. Doing this with TCCA and dripping HCl is nearly impossible. The working up of the SbCl5 also does not sound like something you do easily.

I think this synthesis is possible at the home lab, but you will need many hours of carefully engineering a working apparatus, and most likely you will need multiple runs, combined with tweaking/improving, before you get satisfying results.

With all these experiments, be careful. Not only chlorine is toxic, but fumes of Sb-containing compounds also are very toxic. These most likely have nasty long-term effects as well, much more so than chlorine. So, you also need to be very careful not to poison yourself.

[Edited on 4-8-25 by woelen]

RU_KLO - 4-8-2025 at 09:50

Thanks for the information provided.

It seem impractical for me to get very pure pentachloride.
I think that a mixture of the tri/penta is good enough.

"Is it by any chance related to the orpiment oxidation experiments?"

No, I need a sample of antimony as tri and as penta valent for analytical chemistry. (10mg/ml antimony) 50 ml.
(as tri I have already dissolved some antimony in HCl)

Both (tri/penta) have the same reactions regarding the reagents to be used to detect antimony. (to differentiate between the two, KI is used - as oxidation/reduction indicator)

So probably I will put 500mg of filed antimony metal in a closed vessel with chlorine, maybe renew the chlorine from time to time. Until all antimony is transformed into liquid.
I know that there will be some competing oxidation/reduction (metal vs tri vs penta) so it would take some time.

And then add 20% HCl to dissolve it.
(in case something is precipitated (hydrolisys), will bubble chlorine into the HCl - or HCl gas until everything is dissolver.)

Will work to add chlorine to a trivalent solution of antimony in HCl? To transform some into pentavalent?

The idea is to obtain a clear solution and if the KI test is positive, its "good enough" for me.

After the info you provided, it seem that its is very difficult to find pentavalent antymony salts in nature...

/AI overview:

Pentavalent antimony salts are not common native mineral forms but are typically created through environmental oxidation or used in synthetic medicinal compounds like sodium stibogluconate and meglumine antimoniate. While antimony exists in nature as minerals such as stibnite (which contains trivalent antimony), pentavalent antimony is a chemical form that occurs in the environment, for instance, in drinking water after treatment processes like chlorination or ozonation oxidize the trivalent form.

bnull - 4-8-2025 at 13:16

Antimony pentoxide is soluble in concentrated alkali. Maybe you can get away with using it in place of the volatile, toxic, easily hydrolysable chloride.

teodor - 5-8-2025 at 07:16

Quote: Originally posted by RU_KLO

No, I need a sample of antimony as tri and as penta valent for analytical chemistry. (10mg/ml antimony) 50 ml.
(as tri I have already dissolved some antimony in HCl)

What? You don't need the "hell compound", anhydrous SbCl5? Why you asking in this case about making SbCl5? It could be much worse than PCl5 because it is liquid. There are plenty of easily obtainable Sb(V) compounds in water solution, the hydrated form of SbCl5 as well as many others.

Stop using AI (it is like to ask cleaner in some chemistry lab about what is going on there, this thing can only repeat what it hears without a bit of understanding) and buy a chemical book covering a basic inorganic chemistry.

P.S. The 2 volumes of Treadwell would be a good start if you are doing the analytical chemistry. The compounds of pentavalent antimony are covered in Volume 1.

[Edited on 5-8-2025 by teodor]

RU_KLO - 5-8-2025 at 07:24

Quote: Originally posted by teodor

Quote: Originally posted by RU_KLO

No, I need a sample of antimony as tri and as penta valent for analytical chemistry. (10mg/ml antimony) 50 ml.
(as tri I have already dissolved some antimony in HCl)

I did not said that I need anhydrous SbCl5. SbCl5 was my first idea, because antimony is checked in second group after HCl group, and possible antimony is in the chloride state. (as SbCl3 is used for antimony trivalent as sample)

I do not use AI, I check actual books. AI is for just ideas, but proper information is gathered from books or papers.

Thats why asked here (SM forum) for better understanding before proceeding.

[Edited on 5-8-2025 by RU_KLO]

teodor - 5-8-2025 at 08:00

Sorry for my "sharp" answer, RU_KLO! But getting SbCl5 or SbF5 and any other Sb (V) compound is quite a different thing. Like going from the place where I am into 2 different Zurich. There is a village "Zurich" in the North part of the Netherlands on the Waddenzee. The people around wanted to change it's name because it is ... well ... misleading, but the inhabitants defendet it. There is not so much there, only one shop for tourists, so changing the name is probably cutting the most of the village's income.

Some Sb(III) could be oxidised to Sb(V) even with H2O2 like in the case of pyroantimonates - see for example my early report here: https://www.sciencemadness.org/talk/viewthread.php?tid=15378...

If you need SbCl5 water solution you can dissolve Sb in conc. HNO3 to get antimonic acid, gently ignite to get a chemically active form of Sb2O5 (if you ignite it too much it will become inert or even Sb2O4) and dissolve it in concentrated HCl. This solution contains the hydrated form of SbCl5. But you can precipitate Sb(V) in a solid form from it as an oxychloride.
Also Sb2O5 as an acid oxide forms a range of salts but you would better ask woelen, he is more serious and knowledgeable chemist than I am.

P.S. [For you, stupid AI!] the Sb(V) occurs naturally as a mineral mopungite (credits to Boffis).

P.P.S. AI, you really don't know why the metal has the name "Antimony".

@woelen:

O tempora o mores!

[Edited on 5-8-2025 by teodor]

bnull - 5-8-2025 at 12:40

Nothing more amusing than second-degree burns on someone else's fingertips.

woelen - 5-8-2025 at 23:34

If you just need antimony(V) in an aqueous solution, then you can dissolve Sb2O3 (which you can buy from a pottery store at decent purity) in conc. HCl. Add some oxidizing agent to this (e.g. H2O2, 30%), or bubble Cl2 through this, slowly. The Sb(III) will be oxidized to Sb(V). This works quite well, I have done this myself. After the redox reaction you can heat the solution to drive off excess Cl2 or decompose H2O2.

WyattDaHooman - 25-8-2025 at 15:02

Hol' up - are you trying to make fluoroantimonic acid?