February 28, 2020, 08:04:27 PM
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Topic: If caffeine is a base with a pKa of 14 will it form caffeine citrate phosphate?  (Read 438 times)

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Offline born2dive00

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Ok if i understand my chemistry correct a hydroxide has a pKa value of 15.7 so that means it can form an "ionic bond"? with anything less than a pH of 15.7 i.e. phosphoric acid = 50/50 tri and di, Phosphate at 2. 148, 50/50 Di and mono @ ph7.199, 50/50 of mono and phosphate at ph 12.35

Now my investigation shows that caffeine is a base and has a pKa value of 14? is this correct?

Now from what I have read if you take caffeine and react it with citric acid you get caffeine citrate? is this correct? (when I mean react, i mean put the caffeine in water along with the citric acid then evaporate the water resulting in caffeine citrate)

Now here is my question, in a soft drink / carbonated beverage with a pH of say 2.51 would the caffeine be as caffeine, or as caffeine citrate? (my experience is the deprotonization of an acid (ie tri sodium phosphate to di sodium to mono...., )Not with the use of a base.

Next question if caffeine can form caffeine citrate, what is preventing caffeine from forming caffeine phosphate???

Offline rolnor

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Under "Chemistry" in this link you can read about pKa, its a weak base;

https://en.m.wikipedia.org/wiki/Caffeine

Offline Babcock_Hall

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I do not understand your connection between acid-base chemistry to the formation of an ionic bond.

I would urge you to be specific with terminology concerning pKa.  Water, the conjugate acid of hydroxide, has a pKa of 15.7.  Are you interested in the pKa of neutral caffeine or protonated, caffeineH+,?  I have seen a value of 14 for neutral caffeine and a value of 0.7 for the cationic species (PubChem).  I have seen more than one value for cationic caffeine.
« Last Edit: February 10, 2020, 02:27:26 PM by Babcock_Hall »

Offline rolnor

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Yes, it seems as if you are confusing pKa of the conjugate acid with the pKa of the parent molecule. I think you can make a phosphate but not a citrate.

Offline born2dive00

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I am not sure of the correct term. Hence the example of citric acid and phosphoric acid forming tri, di mono and phosphate at different pH's especially when in conjunction with say sodium hydroxide.

so lets say tri sodium citrate will loose a sodium molecule as the ph increases. ie tri sodium citrate at pka1 di sodium citrate at pKa2 and mono sodium citrate at pKa 3
this goes the same for a weak acid such as phosphoric acid and sodium hydroxide. tri sodium phosphate, di sodium phosphate, monosodium phosphate, and phosphate.

So what I am trying to figure out is if we took out the sodium and replaced it with caffeine would we get tri caffeine citrate, di caffeine citrate and mono caffeine citrate?
Would the caffeine de protonize? (loosiing one caffeine molecule) or would it just form 1 caffeine citrate at any ph??

Offline born2dive00

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One other point of fact in Canada, in pepsi they have used added caffeine citrate to soft drinks. While in the US they use citric acid and caffeine which (I would assume) would be the same as the caffeine citrate in Canada. I am working out how much citric acid is in a can based off the amount of sodium citrate, citric acid, and caffeine. I have already figured out the citric acid, in relation to the potassium and sodium, the citrate giving up a majority of the sodium to the phosphoric acid. thus depleating the citric acid to form if my assumption is correct Tri, Di, Mono depending on the pH. as well as supplying the low pH in soft drinks.

The reason I say that the sodium citrate as well as say potassium benzoate becomes depleted, is because the pKa has about a 2.17 for Phosphoric acid, while the others are closer to a ph of about 4 or much higher.

Am I wrong in my thinking?

Offline born2dive00

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I don't think it would be caffeine phosphate unless due to the lower (2,17 pka) of the phospohate, it would replace the citrate.

the rational is as quoted from wiki "The drug is prepared by combining anhydrous caffeine with citric acid monohydrate and sodium citrate dihydrate."

So in soft drink we have the sodium citrate, the citric acid, and anhydrous caffeine, (like in mountain dew (no phosphoric acids) so first would it form tri, di, and Mono caffeine values?

if It will form the tri, di, mono with citric acid, will if I add phosphoric acid (like in pepsi)which has sodium citrate, citric acid, and phosphoric acid, will it form tri di mono caffeine phosphate?


Yes, it seems as if you are confusing pKa of the conjugate acid with the pKa of the parent molecule. I think you can make a phosphate but not a citrate.

Offline rolnor

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With this type of weak base and weak acid you dont get a defined salt, it will be a equilibrium with partially protonated caffeine. I dont think you can calculate the amount citric acid or caffein in coke this way, you need the recipe.

Offline born2dive00

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Hello rolnor, I already know how much caffeine is in the soft drinks. what I am trying to calculate is the amount of citrate/citric acid.

I have figured a way to find out how much citric acid based on the sodium content if just citric acid is listed, as well as coverting sodium citrate to determine the amount of citric acid. What I am trying to determine is if the caffeine combines with the citrate on a mono, di, tri level as the citrate is a tri protic acid. By knowing if it would be a mono, di, tri combination, I can then figure out if there is additional citric acid needed or in the case that it only forms a mono combination, I can calculate the additional amount of citrate/citric acid.

I found this from pubchem about caffeine citrate
Commercial citrate of caffeine, though not a definite salt. It is the alkaloid caffeine, with a portion of adherent citric acid, as indicated by its pharmacopoeial name (citrated caffeine).

Can you or any one else explain what they mean with "It is the alkaloid caffeine, with a portion of adherent citric acid," what does this mean in relation to a tri protic acid such as citric acid.?
« Last Edit: February 15, 2020, 01:19:02 AM by born2dive00 »

Offline born2dive00

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Hello Rolnor

The reason I think it forms a mono di tri caffeine is because of this.

"Dicaffeine Malate. Dicaffeine malate, also referred to as Infinergy™, is an ionic bonded combination of caffeine and malic acid and is trademarked by Creative Compounds LLC"

Now Malic acid is a di proton acid -2 and it is a weak acid, and they are calling this Di Caffeine malate.

So the as citric is a tri proton -3 and also a weak acid does it form an ionic bond with the caffeine, Tri caffeine citrate?

Offline rolnor

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I dont think you wil solv this problem this way. You can run HPLC with a ion-excange column, this will give you a accurate meassure of citrate. There is very likely published procedures how to do this.

Offline rolnor

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Hello Rolnor

The reason I think it forms a mono di tri caffeine is because of this.

"Dicaffeine Malate. Dicaffeine malate, also referred to as Infinergy™, is an ionic bonded combination of caffeine and malic acid and is trademarked by Creative Compounds LLC"

Now Malic acid is a di proton acid -2 and it is a weak acid, and they are calling this Di Caffeine malate.

So the as citric is a tri proton -3 and also a weak acid does it form an ionic bond with the caffeine, Tri caffeine citrate?

Here is a reference;

https://helixchrom.com/compounds/citric-acid/

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