ChemicalSolution (Hive Bee)
03-21-02 14:39
No 286049
      Boric anhydride from boric acid  Bookmark   

Could this be made by heating boric acid in a flask fit with a vacuum adaptor and heating under reduced pressure?

SWIM is looking for a way around heating the powder up to 450C
(Official Hive Translator)
03-21-02 18:45
No 286155
      The way to go!  Bookmark   

Dear Julia!

I'm happy to inform you that converting H3BO3 to B2O3 is possible by refluxing borax in toluene for 12 h w/a Dean-Stark. See the 'various formylations' doc on rh's - the anhydride thus made is in a fine powder form.

May i politely ask you, what you intend to use it for?

And may i even more politely ask you what ever beecame of that mysterious quasi-nitroethane?smile


(Hive Bee)
03-21-02 21:07
No 286216
      anhydride  Bookmark   

Really??  I saw a procedure that uses boric acid/toluene/Dean Stark trap.. But not an anhydride prep..

Also, what is borax??  Is it OTC like boric acid is??

Formic acid purification!!!  (theoretical, of course)..

A little research was done here.... One possibility is to distill 77% HCOOH with MEK.  Water and MEK form an azeotrope around 73C (11% water)..  This temperature and the HCOOH/H2O azeotrope temp of 107C are far enough apart that a half-way decent seperation is possible.

Here's another (purely theoretical) idea..  The %composition in the azeotrope of HCOOH and H2O changes with pressure much like other azeotropes.. However, unlike H2O and etOH (which, at 30mm no longer form an azeotrope!), HCOOH and H2O always form an azeotrope at practical pressures. 

As the pressure is increased, the % composition of HCOOH increases.  As the pressure is reduced, the % water increases.. So, at 760mm, the water content is 22.5%. However, when the pressure is reduced to 175mm, the water % is increased to 35%, and at 15mm, it's 40% H2O.. At 45 psi??  % composition is around 15% water..

Now, Julia took these values and plotted them with a best-fit line that gives rise to an exponential function.  From this, it is possible to ESTIMATE the % water composition at other pressures..

If anyone wants to jump in and correct Julia and her math skills, have at it.. She came up with the equation: y=51293*e^(0.1866x)..  y=pressure in mmHg, x=%water composition.

 So, at 5mm, the azeotrope should be close to 50% water.  What does this mean???  It means that 77%, constant boiling temperature HCOOH could be distilled under reduced pressure..   Since HCOOH/H2O is a maximum boiling azeotrope, the contents in the flask will concentrate until the % composition is obtained.  The 77% is distilled under a vacuum of 5mm.  Since the % composition of the azeotrope is 50/50, mostly pure formic acid (in theory) should distill over.  Now, (still in theory) you have a 50/50 mix in the flask..  Time to disconnect the vac and distill under normal pressure.  The first to distill is water.  When the temperature rises to the azeotropic temp of 107, the vac is re-applied.  Again, pure formic acid distills over...  And the process is repeated... etc...

The % composition of HCOOH in water is easily obtained, mathematically, by weighing a known volume of solution (this is high school algebra stuff!!!)

Whew...  This looks like fun.... But the CuSO4 drying looks a lot more practical!!!

(Ubiquitous Precursor Medal Winner)
03-23-02 04:24
No 286829
      Easy part, hard part  Bookmark   

When I want boron oxide, boric anhydride, I heat boric acid in a kitchen pot until it melts, then pour it out on a smooth surface. The hard part is crunching it up. The best way I have yet found, is to use a ball-peen hammer, inside a stainless steel mixing bowl. It gets everywhere, fortunately it's quite harmless. It isn't deliquescent; it only takes up water when it's heated. Am I deluding myself again here?

a half a pints a half a pound a half a world a half a round
Sidearm n. Flask neck tube.
04-03-02 12:55
No 291915
      halfpints boiling method.  Bookmark   

I know this may sound beyond novice, but you can never tell, would you use anything to boil the boric acid with?  H2O etc...

i have tuns of this stuff in my house, unfortunately.  tongue[center][purple]