Do aqueous solutions of p-Aminophenol Hydrochloride remain stable for long time? More generally, does a suitably acidified solution of p-Aminophenol base remain stable for long time?
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Thanks for posting this question. I don't have the answer because I have the same question. However, my guess is that it would be quite stable. in acidic solution, provided that the pH is low enough, i.e. well under pH=5.48, which is the pKa of the amino group in para aminophenol.Do aqueous solutions of p-Aminophenol Hydrochloride remain stable for long time? More generally, does a suitably acidified solution of p-Aminophenol remain stable for long time?
Thanks for posting this question. I don't have the answer because I have the same question. However, my guess is that it would be quite stable. in acidic solution, provided that the pH is low enough, i.e. well under pH=5.48, which is the pKa of the amino group in para aminophenol.
The closest thing to what you try to do here is E-6 CD-2 concentrate. It is, as the name implies, quite concentrated, and it contains a small amount of Sodium Metabisulfite to prevent trouble. It lasts for about a year in an unopened container.
I don't know the answer, so just asking what comes to mind. Wouldn't oxidation likely be an issue like for other developing agents ? Or is the assumption that acidification would prevent oxidation?
Pyrocat stock solutions are known to remain stable for reasonably long time due to the presence of Metabisulphite. Jay DeFehr's Obsidian Aqua is an even more concentrated solution of Catechol and Jay has a batch that has remained stable for over 9 years.
Ah I see, it's just an intent mismatch. I thought you were asking about a solution of only p-aminophenol hydrochloride and an acid, without metabisulfite (which is a weak acid, true).
The question appears to be: how much Metabisulfite may be in your intended solution? E-6 is a lot more limited than regular B&W developers.Pyrocat stock solutions are known to remain stable for reasonably long time due to the presence of Metabisulphite. Jay DeFehr's Obsidian Aqua is an even more concentrated solution of Catechol and Jay has a batch that has remained stable for over 9 years.
The question appears to be: how much Metabisulfite may be in your intended solution? E-6 is a lot more limited than regular B&W developers.
Here is a chemist's response...
Hope this helps,
I agree, except that in the handwritten part I think it should sayHere is a chemist's response...
Sorry for the scan of a hand written document... it is much faster than typing.
View attachment 275576
The p-aminophenol hydrochloride (A in the above) when dissolved in water partially dissociates to form "B". This adds protons to the solution thus lowering the pH a bit.
Conversely, when you dissolve p-aminophenol (B in the above) in water some if it "picks up" a proton to form "A". This removes protons from the solution thus increasing the pH.
The other equilibrium (between "B" and "C") does not enter into this situation significantly when adding these compounds to water in dilute solution since the pKa is quite far from the pH of water... in other words all of the phenolic groups are in the "OH" form.
With regard to pH and stability, the lower the pH the more stable the p-aminophenol solution should be. This is because the protonated amine (is in "A") and the protonated phenol (as in "A" and "B") are more stabile to oxidation than their unprotonated forms.
As for the bisulfate issue, I think that bisulfite would be effective with all phenols. Bisulfite is working indirectly to stabilize the phenolic solution by scavenging any oxygen present. Basically the bisulfite reacts with oxygen (to form sulfate) instead of the oxygen reacting with the phenol.
Hope this helps,
--- Frank
I agree, except that in the handwritten part I think it should say
RO- is more easily oxidized than ROH
where RO- indicates the negative ion cause by loss of a hydrogen ion from the phenol group. (I don't know how to write the - as a superscript in the post.)
@alanrockwood, @Alan Johnson thanks for your inputs!
Though p-aminophenol base is only moderately soluble in water at neutral pH, it turns out that the solubility is much higher at acidic pH. I was able to dissolve 20g of p-aminophenol base using 33ml of glacial acetic acid and water to get 100ml concentrate.This gave me a 20% w/v solution of p-aminophenol base which is quite impressive IMO. Compare this with 8% w/v concentration achieved by Rodinal substitutes like Gainer's EZ Rodinal.
If this concentrate remains stable, then it can be very useful. The acid in the concentrate can be neutralized at the time of use by approximately 0.22g of Sodium Hydroxide per ml of the concentrate.
I added 2g Sodium Metabisulphite to the concentrate today and stored it full in a tightly sealed glass bottle. Will test the potency of the concentrate after three months.
I would also expect the solubility in basic solution to also be higher than in neutral solution.
To give you a point of reference: the CD-2 part in Kodak's E-6 5 liter kit contains 166.2 g/l CD-3 and 5.9 g/l Sodium Metabisulfite.
My writing was imprecise: the "CD-2" in my posting referred to "E-6 color developer concentrate part 2", which in turn comprises CD-3 "Kodak's color developing agent #3" and Sodium Metabisulfite.Wow that's a lot! Is the solubility of CD-2 in water much lower if Metabisulphite is not added?
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