Zilantische - 1-11-2019 at 05:32
Hello, I'm trying to extract caffeine from coffee beans. The main problem that I am having right now is finding the pKa of caffeine's conjugate acid.
Pubchem and other resources say that it is 0.6, but this seems unreasonable to me. I don't think that caffeine's conjugate acid is stronger than
hydrofluoric acid. I am trying to find the pKa to calculate how much acid I should add according to henderson-hasselbalch equation.
Ubya - 1-11-2019 at 06:14
wait what? the henderson-hasselbach equation is used to calculate the ph of a buffer solution, are you trying to do the equivalent of a titration
using that equation?
Zilantische - 1-11-2019 at 08:02
Kind of. I want to have [HA] be in excess by 1-2 orders of magnitude, but I can't plug in a pKa value to the equation because I can't find a
believable pKaH for caffeine. The only value I've found is 0.6, and this is extremely atypical because it is around 6.95 for protonated imidazole. I
think caffeine's pKa should be close to this since there is an imidazole ring in caffeine.
B(a)P - 1-11-2019 at 10:57
https://www.google.com/url?sa=t&source=web&rct=j&...
3.6 according to this.
Zilantische - 2-11-2019 at 11:59
I saw that, but it doesn't make much sense to me. Why would caffeine's pKaH be so much lower than that of imidazole?