p-Aminophenol hydrochloride

[michael_young3]

Is p-Aminophenol hydrochloride a usable substitute for 2,4-

Diaminophenol dihydrochloride? The price difference is quite

substantial, $40/pound versus $200/pound.

[jordan_w.]

Michael -- They are totally different beasts. p-Aminophenol hydrochloride is the active ingredient in Rodinal. 2,4-Diaminophenol dihydrochloride is also known as amidol and is used in some paper developers. Their chemical reactivities are very different.

[nicholas_t.]

AFAIK, p-Aminophenol.HCl is the active ingredient of the Anchell and Troop version of Rodinal, p-Aminophenol --straight--is what's listed on the bottle of Rodinal as you buy it.

[nicholas_t.]

Hey Jordan, while were here, is p-Aminophenol.HCl as bad a chemical as p-Aminophenol in terms of being a carcinogen?

[michael_young3]

Some MSDS:<p>

<a href=http://physchem.ox.ac.uk/MSDS/DI/2,4-diaminophenol_dihydrochloride.html>Amidol</a><br>

<a href=http://ptcl.chem.ox.ac.uk/MSDS/AM/4-aminophenol.html>p-Aminophenol</a><br>

<a href=http://www.palomar.edu/ehs/Chemistry%20MSDS/P-AMINOPHENOL-RING-UL-14C.pdf>p-Aminolphenol HCl</a><br>

<p>

No mention of cancer risk in any of them.

<p>

I don't know what my problem is with amidol. The bulk chemical price certainly catches your attention compared to other ingredients. In the end, it works out to no more than mainstream packaged developer cost.

[jordan_w.]

Nicholas -- I don't know much toxicology but in terms of ingestion they would be the same. The only difference between the hydrochloride and the free base is the acidity of the solution they were crystallized from. If you dissolve them in an alkaline solution they'll both end up as the free base. If you dissolve them in an acid solution they'll both end up as the salt form. The hydrochloride should be more stable in storage.

[chris_gittins]

p-Aminophenol hydrochloride and 2,4- Diaminophenol dihydrochloride are very different chemicals.

 

p-Aminophenol HCl is just a salt of p-Aminophenol. If you're measuring by weight, you'd need to use more of the salt but on a molecule by molecule basis they'd function equivalently once dissolved down in solution.

 

Chris

[rowland_mowrey]

I've got to point out something to you all.

 

Since the p-aminophenol is a base, and the p-amino phenol HCL is neutral to acidic, they will affect the developer differently.

 

If you add p-aminophenol to a solution of sodium carbonate, the pH will remain essentially the same. If you add the hydrochloride, the pH will go down due to the HCl. The 2,4-Diaminophenol dihydrochloride will go down even more due to having 2 moles of HCl per mole of compound.

 

So, if pH is critical, you cannot just substitute molar equivalents of these free bases and their hydrochloride salts.

 

Also, the free bases will become tar like on keeping in the original container, much faster than the salts.

 

Another thing to remember is that if you are compounding a paper developer in particular, and the paper is chloride or chlorobromide, then the Chloride introduced as the HCl will act as a restrainer in the developer and cause loss in speed and increase in contrast.

 

Ron Mowrey

[chris_gittins]

That's true about pH being critical. I was writing with assumption that the developer solution was always going to be quite basic. I don't use Rodinal myself, but looking up the recipe in The Darkroom Cookbook (Formula #26 from 1994 printing), Solution A contains 300 g of potassium metabisulfite in 750 ml of water and Solution B is sodium hydroxide. Skipping the details of proper mixing of A and B, isn't the result going to be pretty basic? My sense is if you used the same mol amount of the non-salt in Solution A you'd probably just end up using less of Solution B in your mix. Although I suppose 300 g of bisulfite might make Solution A more basic than you want the A+B mix.

 

Chris

[rowland_mowrey]

Chris;

 

Sodium hydroxide is not a buffer at all. It just raises the pH and thats it. The metabisulfite is a weak buffer, so when you add a hydrochloride salt of an amine, you may as well kiss an equivalent molar amount of NaOH goodbye because you end up with NaCl which is no buffer at all and is neutral in pH.

 

I have not done the calculations. Indeed, I don't have that formula handy. I'm just saying that if the pH is critical you may observe an unexpected problem by using the amine free base vs using the HCl salt of the amine.

 

One developer, all things being equal in molar concentration, will be 'hotter' than the other by some fraction. Whether it is critical or not is up to the user to decide.

 

Regards.

 

Ron Mowrey

[patrick_gainer]

P-aminophenol HCl is a lot more soluble than the base. That is why you can dissolve so much of it in the first step of making Rodinal. Adding the Potassium metabisulfite immediately precipitates the free base, which is then re-dissolved by adding the hydroxide slowly until only a few crystals remain undissolved. The final stock solution is not as caustic as one might believe from the amount of hydroxide that was added. Most of it has been neutralized by the HCl and the metabisulfite.

 

As to the original question, amidol will develop in acidic solutions. P-aminophenol won't. P-aminophenol has been used in tropical developers. It differs structurally from hydroquinone in that the OH group in the 4 position has been replaced by an amino group.