Catechol and Superadditivity

[Pixophrenic]

The claim is that p-aminophenol is more resistant to oxidation than metol, not the other way round.
Can a link be provided to the quoted Modern Photographic developers 1918 ?
p-aminophenol can be used to make a clone of D-76 (metol only version). it is quite stable at pH ~8.5 but takes about twice as long to develop film.

Here is the link
https://issuu.com/piticu/docs/modern_photographic_developers
The book does not discuss relative susceptibility to oxidation. My claim comes from attempts to handle bases of both PAP and metol, and also watching the aging of fresh and used solutions. However, this book does mention that excess sulfite and bromide inhibits the PAP. Mason, BTW, expresses regret that many other derivatives of PAP that were made in research never made it to the market and apparently lost in competition with phenidone.

 

[Alan Johnson]

Interesting link. I would conclude that by 1918 both in N America (Elon) and the UK (MonoMet, probably monomethyl aminophenyl) Metol was being produced and considering the expenditure involved they probably tried it at high pH but found it not commercial. I will see if there is anything in Mees & James.

 

[Raghu Kuvempunagar]

My Kalogen is over a year old and looks pretty much the same, but its low hydroquinone "clone" is just starting, so no opinion yet.

Interesting! Would be a good experiment to prepare Metolal and Metolal with a hint of HQ at the same time, store them in identical conditions, and observe the degradation over time.

 

[Pixophrenic]

Interesting! Would be a good experiment to prepare Metolal and Metolal with a hint of HQ at the same time, store them in identical conditions, and observe the degradation over time.

Actually, I am not trying to "improve" Gainer's Metolal. In my understanding, the idea of Kalogen was to emulate Rodinal, while my idea here is to emulate a metol-only acutance developer, based on phenolate. Omission of most of HQ (down to equimolar with metol) and careful titration results in much less alkali needed, and the 1:50 dilution pH is only 11.5 as opposed to Koch's Kalogen's 12.3. The "storage time zero" development time is 12 min as compared to 5 min of Kalogen. So, I'll be comparing it to itself to see how it looks like 6mo and 12mo later.

 

[Raghu Kuvempunagar]

Is Kalogen's resistance to oxidation due to the fact that it contains Hydroquinone? Is the phenolate formed by Hydroquinone somehow preventing Metol (or its phenolate) from getting oxidised in Kalogen concentrate?

Interestingly Alan has made a hypothesis in a different thread (one on Neofin Blue) that seems to support the role of HQ in preserving Metol:

"My theory is that normally metol would hydrolyse to methylamine sulfonate and hydroquinone, but when hydroquinone is present in the solution this reaction does not run.Thus HQ is a preservative vs hydrolysis."

 

[Pixophrenic]

No problem. Per liter: metol 13.5 g, hydroquinone 4.5 g, sodium sulfite 180 g, sodium hydroxide 6.35 g. Antifoggants are not added, some current films may not need any. The dissolution sequence is as follows: use water at about 50 C, a pinch of sulfite, then all metol, then the rest of sulfite, then hydroquinone. Upon cooling a voluminous pellet forms. Then I use 20% sodium hydroxide solution and add it with a 10 ml syringe in portions, with mixing. I never made more than 100 ml at a time, if this counts. You could call it "Neokal" if it proves to be of general use. ;-)
According to von Huebl (1918) per 10 g of developing agent you need NaOH to make phenolate: 2.3 g for metol and 7.2 g for hydroquinone.