Sciencemadness Discussion Board

Synthesis of Boron Trichloride?

Jhiggins94 - 20-8-2021 at 01:00

hi, i have recently read that the synthesis of Boron Trichloride is somewhat more realisticly possibly for the amature chemist than that of Tribromide, has anyone done it or have any more details? i beleive it involved running HCL gas through graphite and borax?
any further details would be greatly appreciated :)

horuse10 - 20-8-2021 at 02:29

You have to check the SM library, Handbook of preparative inorganic chemistry (Brauer) p 780

" Fairly large quantities of BC13 can be produced by heating
dilute borax with charcoal in a stream of Cl 3 at temperatures of
400 to 700°C"

njl - 20-8-2021 at 05:19

So it's really just a carbothermal reduction of borax to boron, the boron then leaves the reaction as BCl3. HCl won't oxidize the boron to any meaningful extent here, you need Cl2. Another option would be first forming BF3 as tetrafluoroborate via the reaction of boric acid with KHF2 followed by evaporation. The KBF4 could then be reacted with something like CaCl2. With the right solvent this should leave a mixture of products including the insoluble CaF2 + KF and BCl3, which could be extracted or distilled.

Jhiggins94 - 20-8-2021 at 06:37

great thankyou :) how possible is the first meathod for the home chemist do you think? in terms of availability of reagents the borax/charcoal prep seems to be the only option available to me.
correct me if im wrong (im not a qualified chemist obviously but im eager to learn lol) i assume "dilute borax with charcoal" would mean a dilute solution of borax/DH2O combined with charcoal to form a kind of slurry with Cl2 past through it (at 400-700C), and the vapour given off condensed to produce BCl3?
ive got a feeling im way off but that is what came to mind when i read it haha
also how possible are those temperatures for the amature? would i be able to reach those temps with standard glassware and a bunsen?

Chemcraft - 20-8-2021 at 06:56

Quote: Originally posted by Jhiggins94  
hi, i have recently read that the synthesis of Boron Trichloride is somewhat more realisticly possibly for the amature chemist than that of Tribromide, has anyone done it or have any more details? i beleive it involved running HCL gas through graphite and borax?
any further details would be greatly appreciated :)


We can offer ready-made Boron tribromide BBr3 in sealed glass ampoules. See the link to this product in our online store:

https://chemcraft.su/product/24762




[Edited on 21-8-2021 by Chemcraft]

Jhiggins94 - 20-8-2021 at 08:08

well i would like to learn how to prepare my own in the future but i am going to take you up on that offer i think :)

Chemcraft - 20-8-2021 at 08:26

Quote: Originally posted by Jhiggins94  
well i would like to learn how to prepare my own in the future but i am going to take you up on that offer i think :)


Thank you for the order!

njl - 20-8-2021 at 08:30

It's definitely doable, just not a great source. Takes a good amount of effort to get a commodity chemical. That is however a natural part of this hobby. So. First step is a carbothermal reduction, literally using carbon and heat to reduce another substance. This works well because carbon is cheap, pure, and the byproducts are gasses (CO2 or CO usually). This method applies to many oxides and therefore finds use in industry for sourcing metals from their ores. In your case, you would thoroughly mix powdered borax (boric acid might be better) with powdered charcoal. This is what the authors meant by diluting. Once mixed the vessel is heated for as long as needed for reduction. Even though the reaction is not necessarily favorable (we wouldn't expect something like borax to oxidize carbon by itself), because the product is a stable gas you can reduce a wide variety of oxides so long as heating is maintained. This is not usually done in glass, something like a steel can is better. Now, the authors combine the reduction with a chlorination. One could carry out the reduction, isolate the boron, clean it up, and then react it later with Cl2. They're just cutting out the isolation. This is how metals like titanium are produced from their ores. You can start with grossly impure ore, go to a still impure metal, then convert that metal into a volatile compound (like TiCl4) and distill.

Jhiggins94 - 20-8-2021 at 09:37

no worries chemcraft :)

njl - thankyou very much for the explanation that makes a lot more sense, when i hear dilute i assume it must involve liquid haha
so its using carbon and heat to reduce borax, while the chlorine passing through it is simultainiously chlorinating?
i am a coded welder so making the apparatus wouldnt be a problem, if steel would hold up ok and wouldnt react then presumably a fairly heavy wall steel "pipe bomb" device packed with the borax/charcoal with a inlet on one end and outlet the other passing through a condenser into a chilled recovery flask?
do you happen to know the ratios of borax:carbon that would be required and whether a specific flowrate should be met with the chlorine?

njl - 20-8-2021 at 09:46

A steel vessel might survive a few runs at most if you want to chlorinate simultaneously. It is very hard to find a reaction vessel that can stand up to high heat AND Cl2 for extended periods of time (hence doing the reaction in multiple steps).

As for molar ratios I can't help you off the top of my head. Carbon is usually present in excess since some of it will be lost to burning. Flow rate is hard because it will depend on the exact design of your reactor and the circumstances you find yourself in. If I was you I would just use a large excess of chlorine and allow it to pass slowly through the apparatus.

All of that said, BCl3 would be a gas in these conditions so you would need to actively distill it out of the reaction mixture which is just another layer of complexity.

Jhiggins94 - 20-8-2021 at 13:30

well im not looking to produce huge amounts to be honest, i just like the idea of being able to prepare it if i ever need :)
as the reagents and equipment are all fairly easy/cheap to aquire i will have a go in the future but for now i will just purchase the small amounts i need.
could you not just run the outlet from the vessel through a condenser that is fed with water from an ice/waterbath, surly it only has to be chilled to below 12c to condense? and keep the recovery flask on ice?

draculic acid69 - 21-8-2021 at 01:44

Buying pure boron powder from Alibaba/eBay and dropping br2 onto it in a quartz test tube with ground glass connections heated with a Bunsenburner or a blowtorch is really (realistically) the only option for someone in an amateur setting.
Imagine the below setup with the distilling flask
replaced with a quartz test tube. This way the rxn can be done with only the cost of boron powder and a fancy test tube.everything else is something most of us already have or can be made for peanuts. trying to fashion a metal vessel to survive the rxn seems possible but i
doubt bbr3 at red heat won't lead to catastrophe.
Trying to get a seal on a graphite crucible leading to glassware doesn't seem to be territory we've been before but it would survive the heat, hot metals/salts and maybe the halogens.maybe a ceramic vessel might work if one can figure it out and if ceramics survive halogens.the only other possible option would be a tube furnace which is an uncommon expensive harder to do way of accomplishing this.


images (2).jpeg - 8kB

Jenks - 21-8-2021 at 06:44

The best documentation I could find for lab preparation of boron tribromide is still just the 700°C reaction between boron and bromine. With the high temperature, special materials for the reactor and boron often costing >$1/gram in smaller amounts, I wish for a better way. This thread settles on the reaction of aluminum bromide with boron trifluoride or potassium tetrafluoroborate. This latter chemical is particularly cheap - $17/500g at chemcraft right now. But even though their aluminum bromide ($25/350g) is also amazingly cheap, I found references in my google searches to magnesium bromide working as a substitute, which would make the cost and difficulty in handling of reactants extremely low. What I couldn't find was any procedure explaining the temperature or equipment needed for that reaction: MgBr2 + KBF4 -> BBr3.

[Edited on 21-8-2021 by Jenks]

Chemcraft - 21-8-2021 at 07:04

Quote: Originally posted by Jenks  
The best documentation I could find for lab preparation of boron tribromide is still just the 700°C reaction between boron and bromine. With the high temperature, special materials for the reactor and boron often costing >$1/gram in smaller amounts, I wish for a better way. This thread settles on the reaction of aluminum bromide with boron trifluoride or potassium tetrafluoroborate. This latter chemical is particularly cheap - $17/500g at chemcraft right now. But even though their aluminum bromide ($25/350g) is also amazingly cheap, I found references in my google searches to magnesium bromide working as a substitute, which would make the cost and difficulty in handling of reactants extremely low. What I couldn't find was any procedure explaining the temperature or equipment needed for that reaction: MgBr2 + KBF4 -> BBr3.

[Edited on 21-8-2021 by Jenks]


There is another way.
Chloride and bromide can be obtained by the reaction of triphenyl borate with aluminum chloride or bromide. Accordingly, triphenyl borate is obtained by fusing boron oxide and phenol.
B(OC6H5)3 + AlCl3 --> BCl3 + Al(OC6H5)3

Well the method that is used to obtain boron triiodide is also likely to work for tribromide:
3LiBH4 + 8I2 --> 3LiI + 3BI3 + 4H2 + 4HI
This reaction is carried out in n-hexane.

draculic acid69 - 22-8-2021 at 16:45

Quote: Originally posted by Jenks  
The best documentation I could find for lab preparation of boron tribromide is still just the 700°C reaction between boron and bromine. With the high temperature, special materials for the reactor and boron often costing >$1/gram in smaller amounts, I wish for a better way. This thread settles on the reaction of aluminum bromide with boron trifluoride or potassium tetrafluoroborate. This latter chemical is particularly cheap - $17/500g at chemcraft right now. But even though their aluminum bromide ($25/350g) is also amazingly cheap, I found references in my google searches to magnesium bromide working as a substitute, which would make the cost and difficulty in handling of reactants extremely low. What I couldn't find was any procedure explaining the temperature or equipment needed for that reaction: MgBr2 + KBF4 -> BBr3.

[Edited on 21-8-2021 by Jenks]


Pretty much all boron trihalide synth temps are 700'c -1000'celsius.
The boron powder +br2 apparently happens~300'c making it possible to do in an amateur setting.

Jhiggins94 - 2-9-2021 at 01:21

hi, sorry for the delay, i very much appreciate all input, i received my order from Chemcraft today, took a little while to arrive but the postage was reasonable and the tracking very efficient, very happy and will definatly be ordering again :)