Metol, hydrolysis

[Alan Johnson]

The case of methylamine from post 1 could be different, it may just exist as the ionised base (CH3NH3)+ and OH-.
Like the suggested reaction of hydroquinone, equation 3,post 12, this would lead to an ever increasing OH- concentration.

 

[Gerald C Koch]

The case of methylamine from post 1 could be different, it may just exist as the ionised base (CH3NH3)+ and OH-.
Like the suggested reaction of hydroquinone, equation 3,post 12, this would lead to an ever increasing OH- concentration.

Methylamne is a weak base kb = 4.4 x 10 -4 therefore most of it will exist in unionized form. In addition any attempt to hydrolyze metol with OH- ions would be difficult since the negative charge on the nitrogen atom would tend to repel the negatively charged OH- ions. Remember that in addition to three valence electrons nitrogen has an electron pair.

 

[Alan Johnson]

Observations after I year of storage at 60-80F:
Small bottle- the contents smell of amine. Diluted 1:50 it blackens a film leader in 10 min 20C.
It is now topped up with Protectan and re-sealed.
Large bottle - not opened. Virtually the same color as last year (pic)
Conclusions:
I cannot detect small differences that might exist.
There is some indication that metol might not hydrolyze from Gerald Koch's Kalogen developer, now several years old, and from my testing of old ampoules of Neofin Blue, which still worked.
Neither of these is conclusive as other developing agents that might regenerate the metol are also in these developers.

The improbable formulae I posted above seem doubtful now. In case there is some hydrolysis I would now suggest the metol reduces sodium sulfite to sodium bisulfite and forms a metol oxide.
I will let the experiment run.

 

[Alan Johnson]

Observations after 2 years of storage at 60- 80 F: Identical to those detailed in the previous post.

 

[Murray Kelly]

Thank you Alan. It's looking pretty good still. I should add that I have some FX-2 concentrate sealed in glass and it works even now after 57 years. The carbonate gets added when I want to use it.

 

[GLS]

From an organic chemistry point of view the nucleophilic substitution of the methylamino substituent by OH- seems quite unlikely.

para-aminophenols are known to be very unstable in the presence of oxygen. What you seen is in my opinion just the oxidation to the aza-analog quinone.

Yes, nucleophilic aromatic substitution (SNAr) of a para-amino phenol by hydroxide is not at all feasible. For starters, and as a general note, the aromatic ring of an aminophenol is quite electron-rich and therefore not at all susceptible to SNAr. Moreover, in the presence of hydroxide the phenol functionality will be deprotonated (forming the sodium phenoxide), making the ring even more electron rich.

I agree the oxidation to the imino-cyclohexadienone as drawn is likely what occurs. At that point it is quite reasonable to imagine hydroxide hydrolysing the imine group, liberating methylamine and forming the quinone. However, as Photo Engineer pointed out, there are doubtless many different competing side reactions and equilibira present in solution, so the above is only one possibility.

 

[GLS]

Nearest I found to the hydrolysis of methylaminophenol (metol) is this patent for hydrolysis of p-aminophenol with conversion of ammonium bisulfate to sulfate:
http://www.google.co.uk/patents/US3862247
They do not give an equation but the aminophenol appears to have its amino replaced by OH giving hydroquinone.

Unlike the conditions proposed in the OP though, those of the patent are mildly acidic (the pKa of bisulfates is around 2). Under acidic conditions there will be a small amount of the protonated aniline present at any given time, which can then conceivably undergo SNAr by water to form the hydroquinone as they state. The use of ammonium bisulfate is just to sequester the liberated ammonia in the form of ammonium sulfate, which they then use to regenerate the bisulfate. They are also "heating the crap out of it" as we say in the industry, which no doubt encourages the whole process

 

[Alan Johnson]

I will stay sitting on the fence for the time being.
The puzzle is that if metol is not subject to hydrolysis, why is it not used in preference to p-aminophenol in Rodinal type developers.

 

[Alan Johnson]

Some theory, after 2 1/2 years.
Could metol be reduced by sodium bisulfite present in small amount in sulfite solution at this pH ~14?
From Fig 1 (Ref 1) there is very little bisulfite present at this pH
From Fig 2 (Ref 2,3) the redox potential of sulfite is much less than that of metol, so in theory bisulfite could reduce metol.

Measured potentials for metol developers in sulfite solution (Ref 4, table 4) when converted from Esce to Eh are very close to those given for metol in fig 2.
So in theory, if the reaction occurs at all it must be slow otherwise the potentials in sulfite solution would be shifted downwards from the metol line.

So this theory only shows the reaction is possible but too slow to detect.
Will have to await practical results.Comments welcome.

(1) Sulfite in beer Guido 2016
(2) Theory Photographic Process Mees 1942
(3) https://www.sciencedirect.com/science/article/abs/pii/S0167299101820140
(4) Reduction potential developers Kikuchi Ukihashi 1951

 

[Rudeofus]

No idea how Sulfite should reduce Metol. The EH curve you plotted is for the Metol <===> MetolOX reaction. MetolOX will react with Sulfite to form a Sulfonate.

 

[Alan Johnson]

The Eh - pH diagram is the best I could find for bisulfite . It is proposed that bisulfite could theoretically reduce metol. .The bisulfite would be oxidized to sulfite.
The sulfites Eh is clearly lower than that of metol so a reduction is theoretically possible.
The actual chemistry of it is outside the scope of Eh - pH diagrams.

 

[Rudeofus]

The Eh - pH diagram is the best I could find for bisulfite . It is proposed that bisulfite could theoretically reduce metol. .The bisulfite would be oxidized to sulfite.
The sulfites Eh is clearly lower than that of metol so a reduction is theoretically possible.
The actual chemistry of it is outside the scope of Eh - pH diagrams.

The Eh pH diagram is still related to a specific reaction, and in this case it's the Sulfite/Sulfate reaction in one graph and the Metol/MetolOX reaction in the other. There would be a different curve for reduction of Metol to whatever you may end up with if you reduce Metol. Therefore what the chart shows is that

1. Sulfite is a stronger reducer than Metol
2. Based on this graph Sulfite should fog film like crazy - yet we all know it doesn't. As PE said: "many chemical compounds are really bad at chemistry".
3. Based on this graph Sulfite could reduce MetolOX back to Metol - we also know it doesn't, and that the reaction actually happening is MetolOX + SO3-- <===> Metol-SO3

In other words: the graphs are not very helpful here.

 

[trendland]

The Eh - pH diagram is the best I could find for bisulfite . It is proposed that bisulfite could theoretically reduce metol. .The bisulfite would be oxidized to sulfite.
The sulfites Eh is clearly lower than that of metol so a reduction is theoretically possible.
The actual chemistry of it is outside the scope of Eh - pH diagrams.

I guess that what you find out is clear said (from my point possible) if there would not be the next problem : Temperature!

The reduction of metol would need an input! If it isn't there you can wait several years (and nothing will happen)!
Imput = Katalysator/Energy.,,,
That would mean without a chemical substance wich will set the energy level down (to start the reduction oft methol - you would like to see) you have to find out the window of temperature you would need.
I don't state you will need this here:

But I can imagine it will not work at normal temperaure in the cellar room!

with regards

 

[Alan Johnson]

The Eh pH diagram is still related to a specific reaction, and in this case it's the Sulfite/Sulfate reaction in one graph and the Metol/MetolOX reaction in the other. There would be a different curve for reduction of Metol to whatever you may end up with if you reduce Metol. Therefore what the chart shows is that

1. Sulfite is a stronger reducer than Metol
2. Based on this graph Sulfite should fog film like crazy - yet we all know it doesn't. As PE said: "many chemical compounds are really bad at chemistry".
3. Based on this graph Sulfite could reduce MetolOX back to Metol - we also know it doesn't, and that the reaction actually happening is MetolOX + SO3-- <===> Metol-SO3

In other words: the graphs are not very helpful here.

Yes, I completely agree with this.
But AFAIK nobody ever published any results relating to developer hydrolysis (except the pyrazolidones) and I just wanted to check that reduction by bisulfite is not theoretically impossible.
It seemed a kind of way out idea to me as well. but the data seems to show it is theoretically possible.

 

[trendland]

Yes, I completely agree with this.
But AFAIK nobody ever published any results relating to developer hydrolysis (except the pyrazolidones) and I just wanted to check that reduction by bisulfite is not theoretically impossible.
It seemed a kind of way out idea to me as well. but the data seems to show it is theoretically possible.

I agree with you Alan (theoretically possible) why not?

But at what temperature will it be reduced ? I guess that is your problem - perhaps you should have try beginning 30degree Celsius! And you will see if it will happen ?

with regards

 

[Rudeofus]

But AFAIK nobody ever published any results relating to developer hydrolysis (except the pyrazolidones) and I just wanted to check that reduction by bisulfite is not theoretically impossible.
It seemed a kind of way out idea to me as well. but the data seems to show it is theoretically possible.

The data does not show that Metol can be reduced - there is no data point in this graph referring to reduction of plain Metol. The graph is about the reduction of MetolOX. What would Metol actually be reduced to, if there was a reducer strong enough to do it?

 

[Alan Johnson]

I agree, the data has no predictive value regarding the chemistry. But if it turns out that there is some hydrolysis of metol when the experiment has run for longer, some oxidation reaction would be needed to support this and I cannot see anything else in the mixture given in the OP that might do this apart from the oxidation of bisulfite..So I noted this case here just in case it is needed, it may not be if nothing happens.
l

 

[Raghu Kuvempunagar]

Interestingly there's high concentration developer called Master's Metol which uses, IIRC, 50g each of Metol and Sodium Metabisulphite to make 1000ml (of part A). At this high concentration it's supposed to be long lasting though it might or might not survive for 2-3 years as Alan's concoction has.

 

[Alan Johnson]

Thanks Raghu, I am trying an experiment where Metol 5g, Sodium Bisulfite 5g, Water to 100ml are heated at 100C in an inert atmosphere.
If anything happens I will report, but generally nothing happens in this thread!

 

[Rudeofus]

A mixture of 50g Metol and Sodium Metabisulfite would be sufficiently acidic to not develop at all. Is there a part B to this developer formula?

 

[Alan Johnson]

https://www.flickr.com/groups/67377471@N00/discuss/72157632983815540/
It's an idea of Jay DeFehr to make up as part A as stock solution to be used with a choice of Part B.
I just used the part A as it may indicate if anything happens with the higher bisulfite ion concentration around pH = 4 .

 

[Raghu Kuvempunagar]

A mixture of 50g Metol and Sodium Metabisulfite would be sufficiently acidic to not develop at all. Is there a part B to this developer formula?

As Alan clarified there is a part B which is variable. One can use Carbonate or TEA as per need and taste. It's the part A which is highly concentrated and supposedly long lasting.

 

[Alan Johnson]

Unfortunately the 100C test, post 44, had to be abandoned after a total of 24hrs @100C ,equivalent to approximately 256 days at 20C.
This was due to the plastic container filling with steam then collapsing on cooling. It was not possible to heat to 100C continuously.
There was no visible change in the metol/bisulfite solution after this time so there will be no results for possible hydrolysis at pH ~4.

 

[Raghu Kuvempunagar]

Unfortunately the 100C test, post 44, had to be abandoned after a total of 24hrs @100C ,equivalent to approximately 256 days at 20C.
.

Sorry to hear about the unfortunate end to a very interesting experiment. Just wondering how you arrived at the estimate of 256 days. If I use HC-110 temperature adjustment formula (http://www.covingtoninnovations.com/hc110/) i get exp(0.081*80)*1 = 652 days.

 

[Alan Johnson]

I used the approximate rule that the reaction rate doubles for every 10C increase in temperature.
20C=1day, 30=2 . 40=4 , 50=8 , 60=16 , 70=32, 80=64, 90=128 , 100C=256days