Reading Haist: what is more powerful, hydroquinone or catechol?

Pixophrenic · Jun 19, 2019

Since the thread about glycin apparently acting as silver halide solvent had died away, I have found a couple more of similar historical paradoxes.

Nietz in 1922 was able to summarize Lumiere-Andresen rules which among other things predicted that "a developing agent is more powerful if its two groups are in para arrangement than if they are in the ortho configuration", thus hydroquinone is more powerful than catechol (Haist vol.1, p.155).

On page 170, however, Haist cites Umberger as having stated that converting a developing agent into a better surfactant will improve its electron-transfer capability and, hence, its ability to serve a developing agent. In the subsequent three pairs of examples, catechol is implied to be a more powerful developing agent than hydroquinone.

Are there "undocumented confounders" that are responsible for this paradox or should we be content with the statement of Levenson that " Photographic emulsions are such complex things that it is impossible to predict with certainty what will happen under given conditions merely by working on theory"? So then, perhaps there are conditions when one is more “powerful” than the other, and then there are others when the power ratio is reversed? Such as, in superadditivity with metol or phenidone…since developers containing only one of these two chemicals IMO are a profound waste of both?

Rudeofus · Jun 19, 2019

We should be content with the fact, that the scientific field of photochemistry made huge advances since these two gentlemen published their texts. Developing agents are not just weaker or stronger, but have very specific properties, which can't be ranked on a single scale.

Pixophrenic · Jun 19, 2019

Indeed photochemistry has made great strides, and organic chemistry of phenolic compounds as well. Take the phenomenon of pi (Greek pi) stacking, for example. Yet, we hear people citing Bob Schwalberg over and over that more than 2 developing agents is non-sensical. Or that people ask if they can mix DDX with Rodinal. Levenson, if I am not mistaken, was the one who added phenidone and hydroquinone right into into Rodinal and patented it (Ian, are you listening?). Or take the issue of sulfite. The earliest warning that one should watch the quality of sulfite I got from a book of 1918, but even today it is not common knowledge. I tried to re-start the discussion about Crawley's FX10, but in vain. This is another example of developer which would work quite differently, depending on sulfite quality. So, reading classics is still relevant. Just as a mental exercise, take a look at the Unblinking Eye page on staining developers. How many of those make sense to you? How many are essentially the same?

Alan Johnson · Jun 20, 2019

The main use of catechol is in the staining developer Pyrocat series. I did experiment with hydroquinone replacing catechol but not at carbonate pH. There is a formula that substitutes HQ for Catechol if the real stuff is unobtainable.
See post 8 here:
https://www.photrio.com/forum/threads/pyrochatechin-vs-pyrogallol-comparisons.8879/

Pixophrenic · Jun 20, 2019

Alan, I do not understand what you mean. Were you trying to make a staining developer out of phenidone/hydroquinone in low sulfite? It occurred to me that pH optima for hydroquinone and catechol may be different (higher for catechol), hence the discrepancy in "power",

Alan Johnson · Jun 20, 2019

I edited my post to make it more clear.
In the link post 8 a formula is given which replaces the catechol in Pyrocat by hydroquinone, with some discussion of the difference resulting.,
HQ-phenidone is a good developer at low pH, it is the tanning that does not start until higher pH.

Pixophrenic · Jun 20, 2019

Thanks very much for the link, exactly the thread I need.

Alan Johnson · Jun 20, 2019

If phenidone and to an extent metol and p-aminophenol are primary developing agents adsorbed on the silver bromide crystals then secondary developing agents like hydroquinone, catechol ,ascorbate mainly act by passing an electron to the primary agent (and then to silver bromide reducing it to metallic silver) with the secondary agent forming an unstable semiquinone which often gets sulfonated. With catechol and HQ the semiquinones may crosslink the gelatin causing tanning.
I think that is a summary and extrapolation of the books by Mason and Mees & James.

Pixophrenic · Jun 20, 2019

Alan Johnson said:
If phenidone and to an extent metol and p-aminophenol are primary developing agents adsorbed on the silver bromide crystals then secondary developing agents like hydroquinone, catechol ,ascorbate mainly act by passing an electron to the primary agent (and then to silver bromide reducing it to metallic silver) with the secondary agent forming an unstable semiquinone which often gets sulfonated. With catechol and HQ the semiquinones may crosslink the gelatin causing tanning.
I think that is a summary and extrapolation of the books by Mason and Mees & James.

This is correct, but it tells nothing about the relative activity in such a combination. In the link you provided there is indeed a recipe for Pyrocat HD which substitutes hydroquinone for catechol as 1:1. Consulting my little booklet of von Huebl from 1918, however, I found a table with developing agent comparison, which states that the relative speed of development of catechol and hydroquinone is not the same in NaOH (concentration not listed) and in 5% potassium carbonate. With all artificiality of such a comparison, it is interesting to note that In NaOH catechol is almost twice as fast as HQ, while in carbonate only 20% faster. This does not give a complete curve, but it looks like pH change downward has a more dramatic effect on catechol than on hydroquinone. One could safely extrapolate, IMO, that, at pH below 10.5 there is no way to tell the difference between catechol and hydroquinone as both could work only as secondary agents. "Not at carbonate pH" means below 9.2, so what did you get?

Alan Johnson · Jun 21, 2019

Mees & James 3rd ed p361 has a diagram showing the dependence of the rate of development on pH for Catechol and HQ in 0.2M sodium sulfite.
Here is a sketch of it which seems to show that in this case catechol is more active, but of course it does not necessarily follow that this will be so for
all developers containing one of these two.

Rudeofus · Jun 21, 2019

The development rate of HQ vs. Catechol used alone is more or less irrelevant if you add a primary development agent like Metol or Phenidone.

Alan Johnson · Jun 21, 2019

Rudeofus said:
The development rate of HQ vs. Catechol used alone is more or less irrelevant if you add a primary development agent like Metol or Phenidone.

Do you have any published evidence?
The phenidone- catechol Pyrocat was only invented by Sandy King a few years ago and even if he did a comparison with phenidone-hydroquinone (I dont recollect seeing one) it is highly unlikely to have covered the pH range shown in the sketch.

Pixophrenic · Jun 21, 2019

Alan Johnson said:
Mees & James 3rd ed p361 has a diagram showing the dependence of the rate of development on pH for Catechol and HQ in 0.2M sodium sulfite.
Here is a sketch of it which seems to show that in this case catechol is more active, but of course it does not necessarily follow that this will be so for
all developers containing one of these two.

View attachment 225697

Thank you, Alan, this shows clearly that downward change in pH has a more dramatic effect on catechol than on hydroquinone. Concerning their performance in a combo with metol,
I made a quick and dirty test as follows. First, a solution containing 2 g/L metol, 10 g/L sodium sulfite and 0.1 M carbonate-bicarbonate buffer pH 9.5 was prepared, and a scrap of fogged Foma 100 was developed for 2 minutes, blotted and fixed for 2 minutes. Then the developer was split into two equal portions, and supplemented with either solid hydroquinone or solid catechol, to 5 g/L. Two scraps of film were treated in each as above. After about an hour (lunch break) only the "metol-catechol developer" was supplemented with more catechol, to double its concentration, and two scraps of film were developed as above. Time lapse in transferring from developer to fixer was about 10 seconds. Neither of the two solutions showed any signs of oxidation. The result is shown in the attached file as levels of grey measured on the image. As could be seen from it, addition of hydroquinone has a certain effect on speed relative to metol alone, but catechol seems to have none. Doubling catechol has no effect, and the resultant density in catechol is not different from that achieved in metol alone. It may appear as if it is not very useful to combine metol and catechol, expecting the effect similar to that of hydroquinone, unless the working pH is much higher (like 11), but I have yet to do it. Any suggestions, especially where I may be wrong, are welcome.

Rudeofus · Jun 21, 2019

Alan Johnson said:
Do you have any published evidence?
The phenidone- catechol Pyrocat was only invented by Sandy King a few years ago and even if he did a comparison with phenidone-hydroquinone (I dont recollect seeing one) it is highly unlikely to have covered the pH range shown in the sketch.

I have no specific quote regarding Catechol, since this was a development agent that was apparently completely irrelevant for published articles.

I can, however, give you Willems and van Veelen, "Developing Properties of Alkylhydroquinones and Alkylhydroquinone Sulphonic Acids" from The Journal of Photographic Science, volume 14 p 48ff from 1966: as the alkyl substitution on HQ grows longer, it develops photographic materials faster and faster. HQ < Methyl HQ < Ethyl HQ < Propyl HQ < Butyl HQ. As soon as you put Phenidone into the mix, the speed increase with larger substituent goes away.

This would suggest, that similar things could play out with Catechol vs. HQ: the former seems to attach to silver halide grains better and can therefore - at rather high pH - be used as sole developing agent - just like Ethyl HQ. If you add Phenidone, then Phenidone will stick to silver halide, and adsorption of HQ and Catechol becomes irrelevant.

Alan Johnson · Jun 21, 2019

Pixophrenic said:
Thank you, Alan, this shows clearly that downward change in pH has a more dramatic effect on catechol than on hydroquinone. Concerning their performance in a combo with metol,
I made a quick and dirty test as follows. First, a solution containing 2 g/L metol, 10 g/L sodium sulfite and 0.1 M carbonate-bicarbonate buffer pH 9.5 was prepared, and a scrap of fogged Foma 100 was developed for 2 minutes, blotted and fixed for 2 minutes. Then the developer was split into two equal portions, and supplemented with either solid hydroquinone or solid catechol, to 5 g/L. Two scraps of film were treated in each as above. After about an hour (lunch break) only the "metol-catechol developer" was supplemented with more catechol, to double its concentration, and two scraps of film were developed as above. Time lapse in transferring from developer to fixer was about 10 seconds. Neither of the two solutions showed any signs of oxidation. The result is shown in the attached file as levels of grey measured on the image. As could be seen from it, addition of hydroquinone has a certain effect on speed relative to metol alone, but catechol seems to have none. Doubling catechol has no effect, and the resultant density in catechol is not different from that achieved in metol alone. It may appear as if it is not very useful to combine metol and catechol, expecting the effect similar to that of hydroquinone, unless the working pH is much higher (like 11), but I have yet to do it. Any suggestions, especially where I may be wrong, are welcome.

View attachment 225711

Formulae you use are like D-76 with low sulfite and high pH and its catechol analog. Appears to me (top right of your test strips) catechol gives higher density than HQ .
But this may be an illusion as all have high density.
To separate the density of the strips more I would suggest developing a correctly exposed film with a good range of tone densities cut into strips in the dark and tank developed.
To give a longer development time dilute your developer maybe 1+2 or 3.
This should give a more conclusive result.
I don't understand the point of adding extra HQ or Catechol so would omit that.supplement experiment.

Pixophrenic · Jun 23, 2019

Alan Johnson said:
Formulae you use are like D-76 with low sulfite and high pH and its catechol analog. Appears to me (top right of your test strips) catechol gives higher density than HQ .
But this may be an illusion as all have high density.
To separate the density of the strips more I would suggest developing a correctly exposed film with a good range of tone densities cut into strips in the dark and tank developed.
To give a longer development time dilute your developer maybe 1+2 or 3.
This should give a more conclusive result.
I don't understand the point of adding extra HQ or Catechol so would omit that.supplement experiment.

Thank you for the suggestions, Alan. Indeed, this needs a repetition with dilutions. However, I already went on and repeated it at pH 12. Metol needed to be adjusted so as to produce a relatively small density at 2 min. Thus I ended with the following: metol 0.4 g/L, sulfite 2 g/L, tri-sodium phosphate 8 g/L. Note that this is a newly made solution, not a dilution/supplementation. This was split into two portions, and supplemented with either hydroquinone or catechol at 1 g/L (the same ratio to metol as before). The result shows that at this rather extreme pH both agents give a substantial acceleration to metol, but catechol falls a little behind. At this point, however, I am not sure if the density is produced mostly by hydroquinone or catechol respectively, so this needs a control without metol.
I also read a thread on Windisch compensating formula (catechol-caustic), which ended in 2018 on a hanger. So, what you are suggesting is that I essentially pick up and do a comparison with real images the last poster promised. I would not do it on Foma film, though, and I am going to use Stouffer wedge on lightbox.

bnxvs · Jan 30, 2021

What do you think - it makes sense to consider catechol as an alternative to hydroquinone sulfonic acid? If it really is less active than hydroquinone ... Hmm.

Rudeofus · Jan 30, 2021

Activity of developers is pH dependent, and with a different dependency for each development agent. Making a comparison at one given pH, or even worse: with on amount of some specific alkali, will not tell you much about a developer's activity. There are also other aspects than activity which determine a developer's merit: reactivity of its oxidation products, tendency of its oxidation products to stick to the grain etc.

bnxvs · Jan 31, 2021

And if we move away from common phrases?

Pixophrenic · Jan 31, 2021

Rudeofus said:
Activity of developers is pH dependent, and with a different dependency for each development agent. Making a comparison at one given pH, or even worse: with on amount of some specific alkali, will not tell you much about a developer's activity. There are also other aspects than activity which determine a developer's merit: reactivity of its oxidation products, tendency of its oxidation products to stick to the grain etc.

Rudeofus, you as a guy who does not hesitate to repeat experiments that are possibly described in a book by one of the classics, could also do what one of the previous posters suggested. I did not do it, because I found that I asked the initial question incorrectly. The answer is that at a certain pH catechol is more active than hydroquinone, while at another it is the opposite. It was not clear to me until I re-discovered it in an article by Dickerson, who built pH dependence curves for a number of developing agents in a standardized manner. As a result of his study he suggested an extremely rapid developer, using a mixture of amidol and pyrogallol at a modest pH. For some reason, this article was extremely difficult to find (Haist cites it in part). So, the pH dependence curves for catechol and hydroquinone intersect, so there is a pH where their developing activities are identical.

More interesting was the fact that along the way I discovered that while hydroquinone forms a superadditive pair with metol, catechol does not. I must admit, however, that I was taken away by quite another project at that time, so I was lazy to produce a convincing illustration of that.

Pixophrenic · Feb 1, 2021

bnxvs said:
What do you think - it makes sense to consider catechol as an alternative to hydroquinone sulfonic acid? If it really is less active than hydroquinone ... Hmm.

What is your application?

Murray Kelly · Feb 7, 2021

Alan, a question for you. MCM100 uses "Meritol" - an equimolar mix of catechol and PPD. Do you reckon HQ/PPD would make a working equivalent to catechol/PPD for this developer? It still seems to have its followers.
TNX

bnxvs · Feb 7, 2021

Pixophrenic said:
What is your application?

I don’t have any yet. It just thoughts. It would sometimes be helpful to have a less active hydroquinone alternative.

Alan Johnson · Feb 7, 2021

Murray Kelly said:
Alan, a question for you. MCM100 uses "Meritol" - an equimolar mix of catechol and PPD. Do you reckon HQ/PPD would make a working equivalent to catechol/PPD for this developer? It still seems to have its followers.
TNX

Original idea, Murray, I wonder why the old timers never produced such a formula AFAIK. Presumably HQ would regenerate PPD as maybe does ascorbate in Jay DeFehr's Halcyon developer:
https://www.largeformatphotography....?71010-Halcyon-superfine-grain-film-developer.
This is different to the other old PPD developers where PPD was partly a developer but mainly a solvent and and another developer, metol, glycin etc was added to speed up the process at the expense of grain, not to regenerate PPD.

Murray Kelly · Feb 7, 2021

Alan Johnson said:
Original idea, Murray, I wonder why the old timers never produced such a formula AFAIK. Presumably HQ would regenerate PPD as maybe does ascorbate in Jay DeFehr's Halcyon developer:
https://www.largeformatphotography....?71010-Halcyon-superfine-grain-film-developer.
This is different to the other old PPD developers where PPD was partly a developer but mainly a solvent and and another developer, metol, glycin etc was added to speed up the process at the expense of grain, not to regenerate PPD.

Thanks for the reply, Alan. It may be new but I doubt it. I was stuck with the "I've got this, but I need that" quandary.
I am very familiar with the Halcyon developer but in photo.net where I got a bit off topic. Maybe I am again, so I will sit and watch.

Reading Haist: what is more powerful, hydroquinone or catechol?

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