Parodinal - p-aminophenol variation?

[el wacho]

hi,

can one vary the level of p-aminophenol in parodinal by increasing the amount of paracetamol? or is the process of converting paracetamol to p-aminophenol in a sodium hydroxide solution self regulating?

thanks.

 

[Alan Johnson]

The formula of PaRodinal orginates from Sreenath:
http://www.photography-forums.com/acetaminophen-paracetamol-developer-t92639.html
To convert 30 500mg tablets,15g acetaminophen, specifies 20g sodium hydroxide
The chemical equation requires only 8g sodium hydroxide.
I tried this,it did not give complete conversion after 3 days.
I would suggest 10g hydroxide would probably work.
I think the formula specifies too much sodium sulfite,it will not dissolve.
Half the amount of sulfite is adequate.

 

[Athiril]

Hmmmm.

Look at the old documents and Modern substitutes for Rodinal on here.

There needs to be excess for the hydrolysis to occur iirc. What you could do is add a small amount of sodium sulphite instead, after a few drops, drop in acid slowly to neutralise the hydroxide as that should be the solvent for the 4-aminophenol, filter it out, dry and weigh it, make up a solution with that and sodium sulphite and just enough KOH or NaOH?

 

[el wacho]

my question was pointing more towards the idea that whether or not the hydrolysis process, if supplied more paracetamol, would continue to produce more p-aminophenol or that the process reachs a point where, no matter how much paracetamol is supplied, stops the conversion. this is what i meant by being self regulating. thanks for the responses.

 

[Alan Johnson]

The conversion would stop according to the chemical equation when 33.7 g paracetamol is added to the 20g sodium hydroxide used to make 250ml,but in practice a bit less paracetamol since the hydrolysis solution has to be strongly alkaline.The sodium hydroxide is used up and converted to sodium aminophenolate.
Nobody has ever done what Sreenath suggested - fine tune the amount of sodium hydroxide- so his original estimate has more or less got chiselled in stone as PaRodinal.

 

[el wacho]

by titration, do you mean adding the sod. hydroxide drop by drop and stopping when the colour changes? or when a precipitation (if present) clears? what would be the indicator that enough sod. hydroxide had been added?

thanks.

 

[Alan Johnson]

IMO titrating sodium hydroxide is hazardous and best left to experienced chemists who can also figure out the chemical equations.
Also note,the guy in the Phillipines who makes the stuff commercially uses potassium hydroxide which would be closer to Rodinal.