Metol, hydrolysis

Alan Johnson · May 5, 2016

It's not really known why old metol based developers don't last indefinitely.
It might be because the metol reacts with OH ions from the water (hydrolysis) giving hydroquinone and methylamine as in the attachment.(I left out the sulfite for simplicity, they are likely further sulfonated from the intermediate step shown.)
In my experiment I hope to detect the intermediate step from the smell of methylamine.

Test mixture, 40C:
Metol.......................2g
Sodium Sulfite ..........5g
Sodium Hydroxide......5g
Water to...................100ml
This was initially colorless and at !:50 blackened exposed film in a couple of minutes.
It had a very faint smell of amine.
It is stored in a full sealed glass bottle at around 20C.
The experiment may take some months.

Photo Engineer · May 5, 2016

You know that many Metol developers have a strong odor when they fail. It could be any number of things..

PE

Alan Johnson · May 5, 2016

Sorry, should have made clear, I'm looking at the special case of failure in sealed bottles, not by oxidation.

Photo Engineer · May 5, 2016

I've smelled that odor in sealed bottles that went bad.

We mixed gallons of developers and inevitably unused sealed bottles would go bad with a strong odor. We called it "the breath of death" it was so bad.

So, I could have been clearer too. Sorry.

PE

Gerald C Koch · May 5, 2016

PE is right many reactions are possible. Metol can be looked at both as an aniline derivative or a phenol derivative. Both basic structures are host to several different reactions. My experience with both Rodinal and a similar concentrate made with Metol indicate no rupture of the N-C bond even in highly alkaline solution. No distinctive fishy odor of methylamine. Any reaction would most likely be an attack of the phenolic ring. Metol is a remarkably stable developing agent.

There are several developers which can be lumped under the term metol-caustic. Many years ago Kodak sold HDD in Europe. In this country BKA sold Ethol Blue. Neither product seems to have had any storage problem as you would anticipate. Ethol Blue was on the market for about a decade.

Alan Johnson · May 5, 2016

I mean lasts a seriously long time. My Azol (Rodinal clone) is now 68 years old. It was working at 66 when last tested.
(there was a url link here which no longer exists)
My Perceptol in a sealed bottle expired after about 3 years IIRC.
Afraid that's the only example I have.

Photo Engineer · May 5, 2016

Does anyone have a formula for Kodak HDD?

PE

Gerald C Koch · May 5, 2016

Photo Engineer said:
Does anyone have a formula for Kodak HDD?

PE

Geoffrey Crawley made an educated guess as to the formula.

Metol ………………………………………………………………………………………… 2.0 g
Sodium sulfite (anhy) ……………………………………………… 1.0 g
Sodium hydroxide ………………………………………………………… 0.5 g
Potassium iodide, 0.001% ……………………………………… 5.0 ml
Distilled water to make ………………………………………… 1.0 l

Photo Engineer · May 5, 2016

Thanks. It is the Iodide with modern films that was going through my mind lately regarding Crawley formulas.

PE

Alan Johnson · May 6, 2016

If the solution in the OP eventually loses developing activity, the non-oxidative removal of hydroquinone intermediate would have occurred.
For reference here is a possible path:

Photo Engineer · May 6, 2016

The usual path leaves an OH in the 4 position making HQ Mono Sulfonate, which is a poor developer under some conditions.

PE

Alan Johnson · May 6, 2016

Thanks. Perhaps I reinvented the wheel, it may be similar to the pH rise in fresh D-76.

Gerald C Koch · May 6, 2016

As PE points out the equation given is incorrect. What would be formed is hydroquinone monosulfonate. You do not lose a OH- group but add a HSO4- group at one of the available positions on the ring. This only happens when hydroquinone is oxidized. Hydroquinone monosulfonate is a weak developing agent. It is produced in D-76 replenished systems. Kodak used it in starter solutions for various B&W developers. It is also used in one or more developers for microfilm in order to produce normal contrast.

All 4 open positions on the ring are equivalent due to the symmetry of the hydroquinone molecule. However the naming convention requires that the lowest position number be used which would be 2. Therefore the name 2-sulfonyl hydroquinone.

Photo Engineer · May 6, 2016

You should get 2 Sulfonyl, HQ though, with 2 OH groups at 1 and 4 and the SO3- Na+ at the 2 position as shown by Haist and Mees.

PE

Alan Johnson · May 6, 2016

I think Gerald and PE are referring to the sulfonation in presence of oxygen, Mees &James 3rd ed p 289.
I am referring to anaerobic conditions , I don't think this case is published but I don't have Haist.
The point of my equation 3 is merely to show that an equation can be balanced so the anerobic reaction of HQ is not theoretically impossible.

Gerald C Koch · May 6, 2016

Alan Johnson said:
I think Gerald and PE are referring to the sulfonation in presence of oxygen, Mees &James 3rd ed p 289.
I am referring to anaerobic conditions , I don't think this case is published but I don't have Haist.
The point of my equation 3 is merely to show that an equation can be balanced so the anerobic reaction of HQ is not theoretically impossible.

The problem is that in a closed system such as is described there is nothing to drive the reaction. You would need a way of removing the OH- ions. Just because an equation can be balanced does not mean that it occurs. It is better to work with the two half reactions using electrons e-, H+ and OH- ions to balance each half reaction.

Photo Engineer · May 6, 2016

I think I have to go with Gerry. Unless you have totally oxygen free water, this reaction will take place up to the amount of dissolved oxygen which is in accord with the literature.

PE

Alan Johnson · May 6, 2016

I'll bet on hydrolysis of both metol and a similar effect with hydroquinone as being the reason they are often made up as two part developers.

Photo Engineer · May 6, 2016

I'll leave it to the data analysis.

PE

Alan Johnson · May 8, 2016

Here are two bottles of the solution from post 1 at the start of the experiment. They will be kept in a dark cupboard at room temperature.
The small 100ml bottle will be used for any intermediate tests.
The large 270ml reagent bottle has its ground glass stopper sealed with Vaseline to prevent any ingress of air.

idamia · May 10, 2016

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.

Alan Johnson · May 10, 2016

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.

Gerald C Koch · May 10, 2016

I quote from the paper. "hydroquinone is made by the ammonium bisulfate hydrolysis of paminophenol. The p-aminophenol is contacted with 1.2-12 moles of ammonium bisulfate per mole of paminophenol in an aqueous solution at a temperature of about 200-300 C. for a time sufficient to hydrolyze the p-aminophenol to the corresponding hydroquinone." It also goes on to state the composition of the hydrolysation medium must contain ammonium bisulfate. None of these conditions are present in the proposed experiment, pH, ammonium bisulfate, temperature, unsubstituted paraminophenol, ... For substituted aromatic compounds the groups present on the ring effect the reaction. Substitution on the nitrogen can either push electron charge into the ring or put it out.

Alan Johnson · May 10, 2016

I daresay the patent relies on the bisulfite -> sulfite reaction to remove the product of the first reaction, which reaction (attachment) may be similar to that in my post 1.
I don't yet have an explanation for how the methylamine would get removed in the case of the hydrolysis (or not) under investigation.
So I agree the patent bisulfate process is different but it is as close as other literature gets.

Rudeofus · May 10, 2016

If this reaction relies on Bisulfate to Sulfate conversion (BTW: Alan, note, it's Bisulfate/Sulfate, not Bisulfite/Sulfite), and if the composition given in this patent is somewhat representative, then it seems to happen mostly in crazy acidic environment, very unlike our photographic developers.

Metol, hydrolysis

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