angelhair
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Registered: 14-4-2008
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Gasing Sodium formate
I'm attempting to gas Sodium formate to Formic acid following German patent No 414,312. 1933
"300 kgms of dry neutral sodium formate were introduced into 500 kgms of highly concentrated or anhydrous formic acid in a vessel provided with reflux
and an efficient stirrer. A vigorous stream of dry hydrogen chloride was passed into the solution which became strongly heated.
The passage of hydrogen chloride was continued whilst further quantities of sodium formate were gradually introduced, until the vessel was filled to
the desired height. After stopping the stream of hydrogen chloride, such a further quantity of sodium formate was added, that all the hydrochloric
acid was fixed, after which the mixture was subjected to to vacuum distillation.
95% of the theoretical yield of 99% formic acid were obtained. The product contained only 0.5% of hydrochloric acid."
I made Sodium Formate starting from Glycerol and Oxalic acid. Then I added that and some 85% formic acid, that I made from Sodium Formate and H2SO4,
into a 1L reaction flask with a 100mm neck. I added a condenser, overhead stirrer and gas tube.
I added 2.5 moles formate to the acid which created a fair bit of heat then I started gassing quite fast and it got hot, I'm guessing 60 deg C. I
could see NaCl starting to form and then after dropping more than 4 moles of H2SO4, I was supprised to see that my stirrer was still working, unlike
Calcium or Sodium Formate with H2SO4.
I was counting on seeing HCl gas escaping to indicate conversion of the formate. That's what I wanted to see before adding more formate, but the flask
was coated with a formic fog and I couldn't see anything comming out of the condenser and CaCL2 guard tube.
Can I use a pH probe for this or should I do it in an open beaker in an ice bath and wait for signs of escaping gas?.
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angelhair
Hazard to Self
Posts: 81
Registered: 14-4-2008
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Well I did use a pH probe, it wasn't that much help but it did give some indication of what was happening. After all the formate was added, the pH was
2.1 then went down slowly to 0 and that's when I stopped. Still didn't see any gas escaping.
After vacuum distilling, I ended up with 66% of a 89 - 90% formic acid according to its S.G. I stoped to soon.
The patent says that Formic acid is a good solvent for HCl. I haven't found any data on that subject, so what I would like to know is, after all the
formate has been converted, how do you estimate how much HCl is in solution?
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