Boric Acid Esters: Green Flame from Borate Ions in Isopropyl Alcohol Solution

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In summary, the flame is green due to the presence of boron and the methyl ester of boric acid can be made by the reaction of boric acid and methanol.
  • #1
Cesium
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I dissolved some boric acid into some isopropyl alcohol and when I burned the solution the flame was green. I am guessing that I am not getting triisopropyl borate and that the flame just burns green due to the presence of borate ions in solution. Adding sulfuric acid would create the ester.

Is this all correct?
 
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  • #2
The green color is due to the presence of boron and tells you nothing about the presence of borate ions or any other ions. It is unlikely that you formed any isopropyl borate without any cooking of the solution.
 
  • #4
I was unable to read the reference you cited, so I can't comment.
 
  • #5
"The methyl ester of boric acid

Take 1 ml of methanol. Add a spatula of solid boric acid to this. Most of the acid quickly dissolves in the methanol. Pour this solution on a clean glass or ceramic surface and quickly light again. This results in a beautiful green flame, which is much lighter than the pale blue flame of pure methanol."

"The nice thing about these borate esters is that they burn with a true green flame. Just like normal fire, but green instead of orange. This looks very cool and one has to see it oneself in order to fully appreciate."
 
  • #6
Thank you for providing me the reference.
A burning test of this kind is not in any way capable to tell the difference between a mixture and a reaction product, The main reason is that it is a destructive test and thus does not allow you to say anything about the formation of new bonds. The way to follow the reaction is by studying the absorption infrared spectrum which will show the disappearance of the OH bonds and the formation of the B-O-C bonds. No doubt this has been done and probably published.
A quick check of the literature shows the following for the methyl analogue.
One gram of boric acid dissolves in 6 ml of boiling alcohol, which means that it does not react.
The tri ester can be made by the reaction of boric acid and methanol under certain conditions described in Schlesinger. J. Am. Chem. Soc. 75,213(1953).
Several other processes are described in six U. S. patents. I can give you the numbers,if you are interested, but what it indicates is that the simple mixing of boric acid and methanol does not give the esters, because patents would not be granted for such a simple mixing procedure.
 
  • #7
but what it indicates is that the simple mixing of boric acid and methanol does not give the esters
My piece of literature must have been flawed. H2SO4 is needed.
The main reason is that it is a destructive test and thus does not allow you to say anything about the formation of new bonds.
Ah thank you renerob. This makes sense.
 
  • #8
I have done this reaction with borax, Na2B4O7.11H2O with sulfuric acid and methanol. I got a nice green color, since sulfuric acid destroys the mineral to give free boric acid, B(OH)3, and also shifts the reaction to the ester side.

Hope this observation helps too.
 
  • #9
In your discussion on boron esters you stated "Several other processes are described in six U. S. patents. I can give you the numbers,if you are interested, but what it indicates is that the simple mixing of boric acid and methanol does not give the esters, because patents would not be granted for such a simple mixing procedure." What are those patents? I'm trying to remove oxygen from boron powers and think this might work
 

1. What are boric acid esters?

Boric acid esters are a type of chemical compound that is derived from boric acid, a weak acid found in nature. They are formed when boric acid reacts with alcohols, resulting in the formation of esters.

2. What are the uses of boric acid esters?

Boric acid esters have a variety of uses in different industries. They are commonly used as plasticizers in the production of plastics, as solvents in paints and coatings, and as additives in cosmetics and personal care products. They are also used as intermediates in the production of other chemicals.

3. Are boric acid esters safe?

Boric acid esters are generally considered safe for use in various applications. However, like any chemical compound, they should be handled with care and in accordance with safety regulations. Ingestion or inhalation of large amounts of boric acid esters can be harmful, and proper precautions should be taken to avoid exposure.

4. Are boric acid esters environmentally friendly?

Boric acid esters are considered to be relatively environmentally friendly. They are biodegradable and do not persist in the environment for long periods of time. However, as with any chemical, their impact on the environment depends on the specific application and concentration used.

5. Can boric acid esters be found in nature?

Boric acid esters are not found in nature in their pure form, but boric acid, from which they are derived, can be found in certain minerals and volcanic waters. Boric acid esters can also be produced by some plants and are used by insects for communication and defense.

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