Very true which is why I said there may be some reactions which take place on mixing. I'm sure that you must have missed this when reading. This was the point of my post. People tend to think that because the MSDS for Rodinal lists potassium hydroxide that the product contains a lot of this alkali. In actuality it combines with the p-aminophenol to form a phenolate and the bisulfite to form sulfite both of which are NOT listed in the MSDS. This is why I said that an MSDS needs to be read carefully and that a certain knowledge of chemistry is needed to get the full benefit of the document.
Yes, you are correct. In this case, the manufacturer may argue that the hydroxide is still the worst of the potential chemicals in the mixture, and the p-aminophenol is going to revert to the form dictated by pH whenever ingested or absorbed, i.e. phenolate at high pH, phenol or phenol hydrochloride (or similar) at low pH (for instance in the stomach). So whether it is listed as p-aminophenol or potassium para-aminophenolate is much of a muchness. In other cases, not stating the final composition on the MSDS may be much more problematic.
I have proven (to myself at least) that it makes no difference in which form the aminophenol, sulphite and hydroxide are introduced as long as potassium to sodium is at least 1:2 (33%) on molar ratio (to attain full solubility). So one has the following options:
For aminophenol: Plain 4-aminophenol, paracetamol (aka acetaminophen, branded Tylenol), 4-aminophenol hydrochloride (aka hydroxyanilinium chloride), metol (aka Elon) etc. The important factor is that at high pH the functional group must be displaced to give the 4-aminophenolate salt along with the salt formed by the functional group itself (eg acetate for paracetamol). This latter salt travels along as non-paying passenger.
For hydroxide: Either potassium or sodium. I am sure caesium or lithium will also work, if you want to try
.
For sulphite: Either sulphite or metabisulphite. If sodium hydroxide is used, then sulphite MUST be potassium version. All potassium is no problem, but all sodium will FAIL. For metabisulphite, additional hydroxide is needed. One can think of metabisulphite as "compact" sulphite which is "expanded" by the hydroxide. The worst case that will still work is sodium hydroxide with potassium metabisulphite, as it gives very close to the 1:2 ratio of K:Na.
A typical final composition needs to contain:
0.5 mol/L 4-aminophenolate
1.1 mol/L hydroxide
1.58 mol/L sulphite
<3.2 mol/L sodium (4.76 total K + Na is typical if paracetamol is used)
Part of the sodium/potassium content will be in the form of acetate, chloride or sulphate, in a 1:1 molar ratio with the aminophenolate, unless pure aminophenol is used rather than one of its derivatives.
I created a calculator to help those who want to play around with making their own developer. The final product will essentially give Rodinal results, and is long-lived. Paracetamol does not oxidise immediately, as it takes anything from a few hours to days for it to convert it to the aminophenolate. For that reason, it makes a very clear developer with no crystal formation when it cools down. There are formulas that end up with 0.4 mol/L aminophenolate, that use sodium sulphite and sodium hydroxide. This produces a developer with much inferior keeping properties, and which is plagued by excessive crystallisation.
Link to calculator:
(there was a url link here which no longer exists)
