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Author: Subject: Alternatives to sulphuric acid for make ethyl borate
Steamboy
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[*] posted on 4-2-2017 at 02:25
Alternatives to sulphuric acid for make ethyl borate


I am trying to make triethyl and trimethyl borate, however I don't have the concentrated sulphuric acid needed for the classical reaction of boric acid and methanol/ethanol.

What I can use or do?
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Hexavalent
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[*] posted on 4-2-2017 at 08:45


The preparation of borate esters has been discussed before.

http://www.sciencemadness.org/talk/viewthread.php?tid=10778

I suspect that concentrated phosphoric acid could also be used instead of sulfuric acid, however if you can't access sulfuric then I imagine you don't have phosphoric either.

Concentrated sulfuric acid is available in many regions as drain cleaner. Look for white plastic bottles, usually in a plastic bag as secondary containment. It may have some contamination but is usually fine; if it's particularly dirty then cleaning by distillation should resolve the matter. However, if you ask a question like the one above, then you should steer clear of attempting this. I'm not being condescending, but boiling sulfuric acid is really not something to be taken lightly.

You may be able to find phosphoric acid OTC as rust remover or a similar product, though I believe that concentrations can vary significantly between regions and manufacturers.

[Edited on 4-2-2017 by Hexavalent]




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nezza
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[*] posted on 5-2-2017 at 02:26


The sulphuric acid acts a a catalyst and a desiccant removing the water produced by the reaction. I doubt phosphoric acid would work anything like as well.



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[*] posted on 5-2-2017 at 02:30


Quote: Originally posted by nezza  
The sulphuric acid acts a a catalyst and a desiccant removing the water produced by the reaction. I doubt phosphoric acid would work anything like as well.


It doesn't need to work as well as sulphuric acid; it needs to work better than nothing.
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[*] posted on 5-2-2017 at 06:52


Metaphosphoric acid might work. It's an even better desiccant than sulfuric acid. However, it's a pain in the rear to make, because it is made by calcining phosphoric acid, and when hot it eats glass.

[Edited on 5-2-2017 by ave369]




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DJF90
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[*] posted on 5-2-2017 at 14:00


Start with boric anhydride. It can be made by heating the acid under suitable conditions.
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[*] posted on 5-5-2017 at 16:36


Making alkyl borates is actually stupidly easy, if the alcohol forms a low-boiling azeotrope with water, or has a higher boiling point than water. I believe this is true of every alcohol except methanol. You just add boric acid to your anhydrous alcohol, then heat it to boiling. This has been confirmed to work with n-butanol and even isopropanol, and almost certainly works with ethanol. However, there's a good chance that what's being produced is mono- and di- alkyl borates and not the trialkylborates, but if your goal is say, making a solution that burns green, this is good enough.

With longer-chain alcohols though, the flame will be yellow due to soot formation/black body radiation, so you may need a special burner to see the green color very well.
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[*] posted on 5-5-2017 at 18:21


Boron trioxide can itself serve as the dehydrating agent at a cost of 50% theoretical yield relative to boron:

B2O3 + 3ROH >> (RO)3B + B(OH)3

I think it is possible to distill trimethyl borate out of the rxn mixture if the methanol is entirely consumed. Otherwise the boiling point of methanol is lower than that of trimethyl borate.

Also, I suddenly had a thought:

B2O3 (l) + 2NaPO3 (l) >> 2 NaBO2 (l) + P2O5 (g)?

B2O3 boils at 1800 C. P2O5 however boils at a mild 360 C.
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