Fantasma4500
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Concentrated formic acid?
has anyone here tried to do the forbidden, concentrating formic acid, or making it with H2SO4?
i have... 78% formic acid and would rather want 88% -i believe thats where the azeotrope starts
but i also found some hints saying that it is also doable to make 99%
so im thinking. if using H2SO4- starting at 98%
100mL of that, will remove and bind with 28 mL of water
ending up at H2SO4's azeotrope: 70%
78/88 = 10mL- so 300mL 78% formic acid to 88% could be done with (i know a slight bit off the math) 100mL H2SO4
is this safe? it appears theres practically no ways of detecting carbon monoxide in which formic acid will break down into
i was thinking obviously the H2SO4 has to be added very carefully to the formic acid
and then i thought yet further... if i use anhydrous sodium formate, then react this with 70% H2SO4- then it could form 99% formic acid?? the formed
Na2SO4 should also be able to bind with some of the water
on a sidenote, since DCM is gonna be difficult- i was hinted that ethyl formate has a quite low boiling point and also smells nice, and its about
8g/100mL solubility- and might be a lot lower in a saturated salt solution
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clearly_not_atara
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Why not use a less acidic dehydrating agent? You could probably distill formic acid over MgSO4 or CaCl2 or something? H2SO4 seems like a poor choice
here.
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Boffis
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I have seen a reported procedure using azeotropic distillation with n-heptane to remove the water, benzene and cyclohexane may also work. Have you
tried freezing it?
Conc. sulphuric acid is a very bad idea as the product is carbon monoxide not anhydrous formic acid.
If you are trying to make simple formate ester, 78-80% acid works fine if you are patient.
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Fantasma4500
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the product is CO if the H2SO4 is anhydrous, and i suppose with some heating too. going above 88% formic acid using H2SO4 above azeotropic does this
yes
fractional distillation sounds like a lot of hassle, and contaminated product
i did think of anhydrous salts, theyre bothersome to make and especially to recycle
but what about formic acid using 70% H2SO4?
since the H2SO4 is converted to Na2SO4 and formic acid, the water will have to go somewhere- and this is then where adding more H2SO4 to then remove
that water would get interesting
usually i would just give it a go but i know CO poisoning first hand
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clearly_not_atara
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According to Schierz, anhydrous oxalic acid can be used to dehydrate formic acid:
https://pubs.acs.org/doi/pdf/10.1021/ja01655a021
"Formic acid was prepared by dehydrating an 85% acid by warming to about 50 C and then adding an amount of anhydrous oxalic acid sufficient to
combine with the water present. The liquid when cooled was decanted from the crystals of hydrated oxalic acid and distilled."
The same paper mentions that the decomposition of formic acid by 85% sulfuric acid begins already at 45 C. Furthermore, at distillation temperatures
(105 C), even oxalic acid will decompose formic acid, even though it is 100 times weaker than H2SO4! We can infer that combining formic acid
with sulfuric acid in any concentration remotely near desiccation is a very, very bad idea.
[Edited on 10-5-2022 by clearly_not_atara]
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Fantasma4500
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yes, i think i might need to clarify H2SO4 would only be used for dehydrating.. 78% to 88%- which the azeotrope of formic acid starts, and which is
where H2SO4 becomes dangerous to have in concentrations above 70%- azeotropic concentration
but i still dont quite get.... H2SO4, 70%- NaFormate - that should still be grand? ill try combining 70% H2SO4 after cranking the math for water
content and NaFormate
very interesting with the oxalic acid- due to its generally low solubility, i dont think theres much reactions that would care much about the slim
amount of oxalic acid still present after decantation- and maybe cooling it down properly. seems like a very doable method, and with doughs oven
drying method of just simply giving it plenty long time it should work out pretty great
apparently I2O5 iodine pentoxide can be used to detect CO, its made by dehydrating HIO3 at 200*C, HIO3 MP is 110*C
edit: i did the math and turns out using 96% H2SO4 90.6% formic acid is formed- the reaction with ethanol as im planning to use it for forms a bunch
of water, specifically 26g water per 100g NaFormate
add 100g NaFormate to 70mL EtOH
add 75mL H2SO4 96%
75mL H2SO4 96% removes 19.5mL H2O
26.3g H2O is formed
67.6g formic + 7mL H2O = 74.6 = 90.6% formic acid
naturally this is carried out with some stirring in sealed up distillation apparatus- it might make sense to do a small test of this in test tube and
attach a tube to it leading into water to see how much- if any CO is really formed during this- with luck nothing is formed as the formic acid would
instantly react with the ethanol to form ethyl formate
looking about i dont see much realistic options for removing CO, it is a bit lighter than air so removing it by fume extraction shouldnt be that big
of a deal
the azeotrope of formic acid is 88%, but the addition could form hotspots- might have to frustrate synthesis time/yields to please life expectancy.
[Edited on 12-5-2022 by Antiswat]
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teodor
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This is probably relevant info for the topic:
(Rodd's chemistry of carbon compounds, 2nd ed, Vol. IC).
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draculic acid69
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Starting from formate Salts to get 88% it said somewhere that 25% h2so4 is best as any stronger than that causes decomposition. So I'd follow that or
avoid h2so4 altogether Also the way to concentrate it from 88% up to anhydrous you can do with Epsom salts, na sulfates, boric oxide or cuso4
[Edited on 13-5-2022 by draculic acid69]
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Fantasma4500
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i just did a run with .. 180g NaFormate, about 10-20% moisture thus 30g excess - 120mL EtOH - 150mL H2SO4 about 68%
the decomposition as i understand it first happens when the acid becomes dehydrating, H2SO4 isnt dehydrating below 70%
i suppose 88% is just not realistic as the best method is H2S- thats even worse than CO
now- im thinking. if a dehydrating acid, turns formic acid +88% of concentration- into CO.. wouldnt this imply that the formic acid +88% is quite
unstable on its own- as its already dehydrated- and thus is so dangerous that its practically useless??
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