Quote Originally Posted by Gerald Koch
I think that it is significant that the Wolfen recipe calls for the potassium sufite solution to be at 55C. This increases the solubility of the p-aminophenol and helps the formation of the phenolate when the hydroxide is added. As more phenolate is formed more pap will dissolve. I would assume that the reaction takes place in a closed vessel to prevent oxidation.

BTW, there is a recipe in the Focal Encyclopedia of Photography that starts with p-aminophenol rather than the hydrochloride.
Gerald, did I miss something? The recipe you gave near the beginning of this thread had 34 kg of paraminophenol and 50 kg of 34% KOH. I calculated 34 kg of the base to be 0.312 kmoles and 34% of 50 kg of KOH solution to be 17 kg or 0.304 kmoles of KOH. That is 0.008 kmoles less than enough to make all possible phenolate out of paraminophenol. If we assumed that the HCl was intended, 34 kg would be 0.234 kmoles and 0.468 kmoles of KOH would be required to make phenolate out of all of it. That would be 26.2 kg, which doesn't compute to be 34% of 50 kg of solution. In other words, I think the equation balances better when the paraminophenol is interpreted to mean the base and the percent solutions are taken to be grams/100 grams of solution rather than grams/100 ml.

I don't have ready access to the Focal Encyclopedia. Could you quote that recipe, please?