Sciencemadness Discussion Board

Increase the solubility of boric acid in a ethanol dissolution

Steamboy - 5-2-2017 at 02:44

I wanted to make triethylborate, however, due to my absence of sulphuric acid, I decided simply make a very concentrated dissolution of boric acid in ethanol.
The main problem is that boric acid has a "solubility" of ~11% in ethanol (my ethanol is ethanol of 96ยบ, the water that it has and produced by the generation of ethylborates give a solubility of ~2%, so, it is actually minor, >10%).

This ethanol-water-boric acid mix that I created doesn't have the properties that I want, ie, I want to obtain a flammable liquid with a green flame. This liquid has an strong orange flame with very little green colours.


I want to obtain a concentration of boric acid bigger than 20% in ethanol, without to lose the flammability (because my objective is, I repeat, obtain a fuel with a green flame).
What products I can add to the ethanol for increase its boric acid solubility, without to lose flammability?

Edit: I read that the addition of hydrochloric acid in water can increase the solubility for boric acid. Does this works also in ethanol?



[Edited on 5-2-2017 by Steamboy]

Sulaiman - 5-2-2017 at 05:06

Although ethanol can burn with an almost invisible flame, it still adds yellow to the flame due to carbon particles,
(methanol + boric acid) is a nicer green


solubility of solids in liquids usually (not always) increases with temperature, often very significantly
I'm not sure about boric acid in alcohols ... look it up, I'd like to know ... :)
Look at the flamability and toxicity of ethanol and methanol, and the pesticide boric acid,
and I'd watch a couple of YouTube videos of 'methanol fire' before starting.

Looking at (and finding) MSDS for chemicals can be tedious, but almost mandatory reading.
MSDS for consumer products can reveal treasures.

personally, I have learned a lot from Wikipedia

P.S. also, boric acid decomposes to metaboric acid above 170 C, and then above 300 C to B2O3,
https://en.wikipedia.org/wiki/Boron_trioxide
you should check their toxicity too.

[Edited on 5-2-2017 by Sulaiman]

[Edited on 5-2-2017 by Sulaiman]

Melgar - 5-2-2017 at 15:25

Ethanol for some reason doesn't produce a green flame at all, no matter how much boric acid it dissolves, even if you dilute it with water so there's little if any soot-forming carbon. The two alcohols that actually do work are methanol and propylene glycol. Propylene glycol burns longer, but methanol is easier to light, and burns faster.

Steamboy - 6-2-2017 at 11:47

Actually I obtained a green flame using the dissolution of ethanol and boric acid (for concentrated such, I have made use of the temperature change) however, if too big quantities are burned, it creates a secundary brighter orange flame that overlays or is mixed with the green flame.

Also, I observed that paper or cotton wet with this liquid, will burn without create such orange flame (until the liquid is consumed, next paper or cotton will start to burn with its orange flame although, curiously, these stay having some green flame traces).


About waste, I've noticed that this liquid creates a white fine layer over the surface where it is burned (and in any surface that is exposed to such liquid). Is this the boron oxide?

[Edited on 6-2-2017 by Steamboy]

Melgar - 7-2-2017 at 11:28

Quote: Originally posted by Steamboy  
Actually I obtained a green flame using the dissolution of ethanol and boric acid (for concentrated such, I have made use of the temperature change) however, if too big quantities are burned, it creates a secundary brighter orange flame that overlays or is mixed with the green flame.

Also, I observed that paper or cotton wet with this liquid, will burn without create such orange flame (until the liquid is consumed, next paper or cotton will start to burn with its orange flame although, curiously, these stay having some green flame traces).


About waste, I've noticed that this liquid creates a white fine layer over the surface where it is burned (and in any surface that is exposed to such liquid). Is this the boron oxide?

The orange flame is probably sodium and/or calcium borate, the boric acid reacting with sodium and calcium from the glass. Glass actually contains quite a bit of those elements, which impart a bright yellow-orange spectrum to just about everything. This would be more the case if the glass was very hot. It's pretty easy to tell an orange flame that's caused by a (usually) sodium spectrum from one caused by black-body radiation from soot particles if you know what to look for. The blue in a flame is caused by carbon monoxide, incidentally, which behaves sort of like a metal in its spectrum due to its free electrons.

If you want a brilliant green flame, you need to forget using ethanol though. (By the way, are you Polish? The only alcohol I've ever seen that was 96% has been from Poland. I guess they just round up to 96 from the azeotropic 95.5, even though I doubt their distillation results in a perfect azeotropic mixture.) Methanol works well. Propylene glycol is beautiful. Ethylene glycol may work, but I've never tried it. Ethanol may have some green streaks in it, but that's the best you'll be able to get without using a different alcohol.

[Edited on 2/7/17 by Melgar]

Dragonsired1 - 23-2-2017 at 14:02

Quote: Originally posted by Melgar  

If you want a brilliant green flame, you need to forget using ethanol though. (By the way, are you Polish? The only alcohol I've ever seen that was 96% has been from Poland. I guess they just round up to 96 from the azeotropic 95.5, even though I doubt their distillation results in a perfect azeotropic mixture.) Methanol works well. Propylene glycol is beautiful. Ethylene glycol may work, but I've never tried it. Ethanol may have some green streaks in it, but that's the best you'll be able to get without using a different alcohol.
[Edited on 2/7/17 by Melgar]


Is it hard to make green flame via boric acid propylene glycol? I didn't found anything useful about this combo.

Tin man - 25-2-2017 at 13:32

I've done many demonstrations where I coloured flames green with boric acid, and denatured alcohol has always worked great for me. But to get the brightest green possible, I would use methanol instead, not only because it burns cleaner, but also because it is more polar, and therefore will probably be able to dissolve more boric acid.

Dragonsired1 - 26-2-2017 at 02:53

Quote: Originally posted by Tin man  
I've done many demonstrations where I coloured flames green with boric acid, and denatured alcohol has always worked great for me. But to get the brightest green possible, I would use methanol instead, not only because it burns cleaner, but also because it is more polar, and therefore will probably be able to dissolve more boric acid.


Yea, that would be awesome with methanol. The problem is, in my country it's strictly monitored ...every drop. And of course it's banned in any products available "publicly". I have, and I'm able to get anything except methanol :(

[Edited on 26-2-2017 by Dragonsired1]

Justin Blaise - 26-2-2017 at 06:39

If you have the set up, you could try destructive distillation of wood to get some crude methanol.

Melgar - 1-3-2017 at 07:46

Quote: Originally posted by Dragonsired1  
Is it hard to make green flame via boric acid propylene glycol? I didn't found anything useful about this combo.

Try dissolving about 1g of boric acid in 10mL of propylene glycol, then burning it in an alcohol lamp. It is a lot slower to dissolve boric acid in propylene glycol because of the viscosity, so try letting it sit someplace warm for a few hours, or overnight, to make sure it goes into solution after shaking the mixture as well as you can. It is also more difficult to ignite propylene glycol, so you will probably need to either use a torch, or burn it as you would wax, with a cotton or paper wick.

[Edited on 3/1/17 by Melgar]

Dragonsired1 - 4-3-2017 at 06:24

Quote: Originally posted by Melgar  

Try dissolving about 1g of boric acid in 10mL of propylene glycol, then burning it in an alcohol lamp. It is a lot slower to dissolve boric acid in propylene glycol because of the viscosity, so try letting it sit someplace warm for a few hours, or overnight, to make sure it goes into solution after shaking the mixture as well as you can. It is also more difficult to ignite propylene glycol, so you will probably need to either use a torch, or burn it as you would wax, with a cotton or paper wick.


[Edited on 3/1/17 by Melgar]


Thank you, as soon as I get my propylene glycol I'll post here results.