Formation of Trimethyl borate

[sheanhung]

I have done the experiment by adding boric acid, methanol and con. sulphuric acid in a test tube. Vapour produced gives a green flame when tested with burning ignited stick.

 

Anyone know the equation for that??

 

from what i have discovered was

H3BO3 + 3CH3OH -----> B(OCH3)3 + 3H20

 

but i am not sure the function of con. sulphuric acid, so i dont know where to put it in the equation

[YT2095]

I`ve never used sulphuric acid for methyl borate, simply dissolving the boric acid in hot methanol, and allow it to cool, and then filter any undissolved boric acid.

the liquid left will burn green

 

edit: I just had an idea what possible use the conc sulphuric has, you state that there`s water produced, conc sulph acts as a deydrating agent in some synths, it doesn`t really play any significant roll in the actual formation of these products though.

[budullewraagh]

the H2SO4 is used to protonate the methanol. the borate then does a nucleophilic attack to displace the water molecule. the H2SO4 also acts as a dessicant, which helps push the reaction forward as products are eliminated

[woelen]

I have done the experiment with methanol, ethanol and boric acid. I had heard of it before, but this thread made me curious and caused me to perform the experiment myself. I was really surprised at the really clean green color of the flame, when methanol is used. With (denatured) ethanol the result is less convincing. The result is added to my website with some nice pictures.

 

http://woelen.scheikunde.net/science/chem/exps/borate_ester/index.html

 

No concentrated H2SO4 is needed for the nice green color. Just methanol and H3BO3 is sufficient.

[sheanhung]

thx~