Metol, oxidation product

[chris_waller]

Could anyone please tell me what the oxidation product of metol is?

And why does it have such a marked restraining effect? I'm currently

running trials with D23, which is returning excellent results at a

dilution of 1:3, but I want to know more about the chemistry of metol.

Thanks.

[rowland_mowrey]

Chris;

 

All of my textbooks and notes are strangely silent on the oxidation of Metol or Elon. All they say is that the oxidation proceeds as expected, or the oxidation proceeds in a manner similar to hydroquinone.

 

From that I would expect that the oxidation produces a quinonoid compound which then sulfonates if sodium sulfite is present as a preservative.

 

You would then go as follows:

 

CH3NH-PH-OH -> CH3N=Q=O -> CH3N-S-OH where

 

PH is Phenyl C6H4

 

Q is the rearranged ring structure of Phenyl.

 

S is C6H3SO3H, the sulfonated product.

 

Just a guess, put in laymans terms and with the poor capability for showing ring structures here.

 

Ron Mowrey

[jordan_w.]

While we're on the subject -- Ron, perhaps you can answer this -- I would love to know what the oxidation product of *phenidone* is. It's basically a cyclic acyl hydrazide with an aromatic ring hanging off the "far" nitrogen... I can think of a few ways to picture the oxidation happening (treat it as a hydrazine or as an aniline) but nothing convincing.

[mskovacs]

Drop the -OH after the "S" group and you'll have something closer to reality (6 bonds to sulfur). That's just a correction, I actually have no idea of the real details.

[mskovacs]

unless you are saying the sulfate group is finding its own home on the ring..

[jordan_w.]

Mike -- I'm pretty sure that sulfite reacts with quinones to form sulfonic acids with the sulfonate attached directly to the aromatic ring. Sulfite behaving like an electrophile in this case.

 

This reaction may have something to do with why phenidone and hydroquinone require sulfite for superadditivity.

[grant_.]

i prefer LSD

[rowland_mowrey]

Jordan is correct. The SO3 attacks the ring directly and does so in the same manner as with HQ, I suspect. I am assuming that it made the free acid in the example, but it would make the sodium salt in a developer.

 

I know nothing about phenidone or its analog dimezone. Offhand, I don't even remember the structures of them except that dimezone is dimethyl phenidone. Oxidation of hydrazines is very complex. I did some research on them at one time, and got lots of products, most of which were unexpected.

 

I'll look into it, but may not find anything.

 

The sulfonated HQ is a good developer. I know nothing about the capabilities of the metol analog.

 

Ron Mowrey

[rowland_mowrey]

All of my texts on developers are silent on phenidone which is 1-Phenyl-3-pyrazolidinone. Even the Merck index only lists toxicity and synthesis information. Usually they hint at oxidation routes.

 

Anything I say would just be conjecture. I've been away from it too long to do this kind of thing. All I know is, it would not react the same way as any of the other developing agents.

 

Ron Mowrey

[silent1]

I remembered from recent research related to coffee developers that phenidone is a pyrazolidone -- a few seconds on Google produced 1 phenyl 3 pyrazolidone, and a structure <a href="http://www.chemicalland21.com/arokorhi/specialtychem/perchem/1-PHENYL-3-PYRAZOLIDINONE.htm">here</a>. There's also a phenidone B (1 phenyl 4 methyl 3 pyrazolidone) which is also listed as demizone (misspelled dimezone?) on one site, and a 4 hydroxymethyl 4 methyl 1 phenyl 3 pyrazolidon that's also listed as phenidone B on a different page, and sounds closer to your description of dimezone.<p>

 

These are all pages offering to sell the stuff; I have nothing to do with any of them.

[jordan_w.]

I'm familiar with the structure of phenidone -- how it oxidizes is a mystery to me. Like Ron I turned to the Merck first with no luck. The chemistry of acyl hydrazides isn't that complex (not nearly as much as hydrazines) but I can't figure out how phenidone would act as a reductant. The difference between dimezone and phenidone isn't significant from a basic chemistry point of view. Maybe it's time to do some basic reading into the redox chemistry of N'-phenylhydrazides.

[Alan Johnson]

An equation for development by metol is given in Basic Photo Science by Attridge & Walls, if I remember correctly. It gets an SO3 minus group attached to the original structure.

[rowland_mowrey]

Jordan;

 

I've been fooled by nitrogen chemistry too often.

 

However, my guess is that the N-N bond would cleave and leave an N-phenyl amino acid. The other nitrogen may stick around leaving an amide or it may hydrolize off and leave the free acid.

 

IIRC, oxidation of CH3-NH-NH-CO-PH gave benzoic acid, benzamide and a bit of tar. Oxidation of PH-CH=N-NH-CO-PH gave a lot of benzoic acid. Phenidone might then give PH-NH-CH2-CH2-COOH or -CONH2. It does not seem to me though that the sulfite is going to react with the benzene ring. Again, pure speculation. My memory is faulty since I did this about 40 years ago, and I don't have any references to look to for help.

 

Doing practical photographic chemistry is more of an art than science, and often you care more about the results than the specific reaction products.

 

I do know that HQ and Metol, when oxidized, react with sulfite. With the oxidation products out of the way, the equillibrium favors more oxidation, so the addition of sulfite increases the rate of the development reaction with Metol and HQ.

 

Ron Mowrey

[tklim]

Hi, everybody, and thank you all for another portion of valuable knowledge. Since the original question mentioned the restraining effect of metol-based developers, I'll permit myself to add my two cents.

 

AFAIK, we owe the very much sought for compensating effect of metol developers not only to the mechanism of its oxidation and subsequent action of the oxidation products, but also to the strong restraining effect of bromide ions (or more generally, halides) released to the solution during development. Metol developers seldom contain potassium bromide, as long as their alkalinity remains moderate, because of the low fogging tendency of the reagent. Bromides are known to slow down the reaction of silver halides reduction in the areas of the negative where the that reaction occurs at the highest intensity, i.e. highlights. The effect becomes particularly pronounced when moderate degree of agitation is applied. Addition of potassium bromide to the stock solution of the developer also destroys the adjacency effect, that's why bromide is avoided in the many acutance formulas available (FX-1, Beutler), even if a higher base + fog density must be tolerated as a compromise.

 

Regards - Tomasz

[chris_waller]

Many thanks everyone for your input - this has been a very informative thread.

[rowland_mowrey]

Tomasz;

 

Very good post.

 

That may be why D76 has endured so long. Low levels of alkali, no bromide, and a moderate silver halide solvent. (sodium sulfite at high level)

 

The sulfite also enhances developability.

 

Bromide in high concentration, released during development in the darker areas enhances adjacency effects.

 

The down side is higher sensitivity to agitation, quick exhaustion of alkali, and sensitivity to dilution or quantity used in drum or tank processes.

 

I may have forgotten most of my synthetic organic chemistry, but I still remember my photographic design parameters. I still consider designing a useful photographic processing solution to be more art than science sometimes.

 

Ron Mowrey

[patrick_gainer]

If science is knowledge, the attainment of science is one of the arts. Still no word wrap here. Maybe it's because of Windows XP.

[jorge_oliveira2]

You guys are way above my knowledge of chemistry, so I will try to help by citing some posts by Michael Gudzinowicz in R.P.D.:

 

Phenidone

 

" From Haist:

 

- Effect of Oxidized Form on Rate of Development - decrease

 

- Effect of Sulfite on Rate of Development - none"

 

Re restrainers:

 

" Bromide acts as a restrainer, and anti-foggant. It is very unlikely that the inhibition or activation of development by oxidation products is due to a bromide effect, or the product acting in a way similar to bromide. Both the restrainer effect and anti-fogging action of bromide appear to be related to the decreased solubility of silver ions in its presence at moderate concentrations (0.35 g/l), and a similar decrease in the rate of reduction of silver ions in solution."

[rowland_mowrey]

Jorge;

 

The Haist reference supports the idea that there is no significant reaction between sulfite and phenidone, or that the reaction product is relatively inert photographically.

 

The quote on bromide is quite well known. The action of bromide is often so strong, I am continually amazed that D76 works so well without bromide and with a mild silver halide solvent.

 

Silver halide solvents can counter the effects of bromide in a developer. Or at least they seem to have that method of action. They increase development and fog which is what bromide restrains. And they act by solubilizing silver which is the reverse of bromide. And, by that logic, iodide is a very powerful restrainer. It can give very unusual effects, especially in emulsions.

 

Ron Mowrey

[jorge_oliveira2]

Ron

 

It's interesting that Michael G. (both a photographer and a PhD chemist) states in another post that he likes more an Agfa formula with bromide to D-76...

[jordan_w.]

The aromatic ring in phenidone is only very weakly activated relative to the aromatic rings in hydroquinone or metol so I'm not surprised that there is no reaction with sulfite. Mind you I couldn't figure out how phenidone oxidizes so who knows? Phenidone and hydroquinone are only superadditive in the presence of sulfite, so I think it's safe to say that phenidone is not superadditive with hydroquinone but rather with the hydroquinonesulfonic acid we described above.

 

The solvent vs. bromide issue Ron raises is a good point. A few months ago I made some efforts to brew a B&W reversal first developer starting from HC-110 dil B. I use HC-110 a lot and wanted a soup for B&W slides that I could build off of it. I added sodium carbonate, sodium thiosulfate and potassium bromide to the mix. Balancing the quantities of these chemicals was quite a task as they work against each other in different ways.

[Alan Johnson]

In Attridge & Walls book it is noted that with phenidone an unstable intermediate is regenerated and only hydroquinone is used up.With metol some may be adsorbed to `break a trail` for hydroquinone and this is irreversibly sulfonated. I'm not sure that with D23 the oxidation product of metol would have much restraining effect,possibly bromide may provide some fringe effect.Book says bromide may psh to the left the reaction AgBr plus electron -> Ag and Br minus

[rowland_mowrey]

Alan, Jorge;

 

You both raise good points.

 

I agree that a bromide containing version of D76 might be better, but I'm also concerned at the low level of Borate buffer in the developer. However, as stated, the 100 g/l of sodium sulfite makes up for this and is a weak silver halide solvent.

 

And these are only questions regarding B&W MQ developers. Just think of the problems in designing color MQs. These have to be adjusted for diffusion effects and the developability differences between layers. Very complex subject.

 

Grant Haist and Dick Henn were my resources for learning about MQ and Phenidone or Dimezone developers.

 

That brings up another point. I always felt that dimezone (dimethylphenidone) was better than phenidone. Yet, I never see it in the literature anymore.

 

Another topic is antifoggants. I learned that benzotriazole was good, but that nitrobenzimidazole and phenyl mercapto tetrazole were as good or better. Any comments?

 

Ron Mowrey

[jorge_oliveira2]

Ron

 

Regarding dimezone - it's almost impossible to find that stuff retail, so we, homebrewers, have to resort to old phenidone ))-:

 

Re anti foggants - I've started with benzo, and just kept on using it (it was sold as Kodak anti fog 1 tablets...). For paper, I really replace bromide for it, since to my eyes (and papers I use), bromide used to leave a green cast on the print. Benzo gives nice, cool tones I like.

[jordan_w.]

Ron, I once read (somewhere -- probably in Haist) that dimezone has slightly better stability to aerial oxidation than phenidone does. But I was under the impression that Kodak developed dimezone as a way around Ilford's patent on phenidone. As regards antifoggants, it would be interesting to know what the molecular mechanism of the anti-fog effect is in these organic compounds. And as for colour MQ developers: it's always been a wonder to me that colour photographic processes actually work reproducibly :)