Metol, oxidation product

[rowland_mowrey]

Jordan;

 

I got the information personally from Grant. We are personal friends and I worked with him at EK. We hold a couple of patents on thermally processed dye bleach materials.

 

Dimezone is a very good developing agent, especially in color products where it can be adjusted to control individual layers. I get the impression that it is better than phenidone for many purposes, but I agree that it is hard to get. Just like CD3 and CD6 now days.

 

As for antifoggants, they work by adsorbing to the silver halide surface at the site of exposure, and they prevent development. But since a fog site is not 'exposed' they seem to go there first. Therefore they inhibit fog before inhibiting image formation. Now that was a simplistic laymans explanation. I didn't mean to be patronizing, but the actual chemistry is very complex and actually outside my field.

 

In color, it is possible to use mixed antifoggants to work on each layer in a different fashion. This is a critical method of adjusting color developers to make them work and give balanced neutral images.

 

It can be done in the film or in the developer. In color, it can be done in the MQ or the CD step. In can even be done in all 3, film, MQ and CD.

 

See the EK web site for E4 process formulas. It can be an eye opener for those that have never seen color MQ and CD formulas.

 

Ron Mowrey

[jorge_oliveira2]

Could you chemist gents pls explain the meaning of 'adsortion' ?

 

Thanks,

[jordan_w.]

Jorge -- Adsorption generally refers to a process where molecules from a solution or vapour are deposited on a solid particle or surface. No strong chemical bonds are formed where the molecule meets the surface, but a collection of weaker physical-chemical forces keeps it there.

[jorge_oliveira2]

Thanks, Jordan

[Alan Johnson]

I believe the bromide has to be generatd from AgBr in the emulsion during development to provide edge sharpening.I cannot find much agreement or original source on metol oxidation product effect."..phenidone is particularly insensitive to bromide ion"(Attridge&Walls p193) so if it is the bromide that does the restraining this would appear to suggest metol for edge sharpness.

[jorge_oliveira2]

I did not do a compare, but from hearsay metol produces more edge effects than phenidone with hydroquinone.

 

Again, from hearsay, it seems that with ascorbic acid phenidone holds well (ascorbic byproducts are acidic and hydroquinone's are alkali)

[rowland_mowrey]

Alan;

 

You are correct. Bromide must be produced from development to produce an edge effect. Iodide is even more effective than bromide in doing this.

 

Bromide or iodide in the developer has the effect of restraining overall development and reducing fog.

 

In fact, any restrainer released imagewise will enhance sharpness. Any restrainer added to a developer restrains fog and development.

 

Ron Mowrey

[Bill C]

>> [Rowland (Ron)] 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 <<

 

I wasn�t going to bother looking, on the assumption that if Ron didn�t have the info, who would? But today, I got a little free time on my hands and looked around a bit.

 

It turns out that there are brief discussions in both �Photographic Processing Chemistry� (Mason; 1966) and �The Theory of the Photographic Process� (Fourth edition; James, ~1977?).

 

Also, the weather was pretty nice so I took a little walk down to the local library to check their books. They have Mason�s 2nd edition (1975) which seemed to have exactly the same section on metol. Also, they have the THIRD edition of �The Theory of the Photographic Process� (Mees and James; 1966); this did NOT seem to have the pertinent information.

 

Not being a chemist, I won�t try to interpret or explain (I�m afraid Jordan or Ron will catch me on something), but here are a couple exerpts:

 

From Mason,

�Metol is a derivative of para-aminophenol, and most of the reactions described will be characteristic of para-aminophenols in general.�

�

 

Next, some structures are shown with discussion and rough values for K.sub.a and K.sub.b.

�

 

�The oxidation of para-aminophenols can proceed in two one-electron steps, the intermediate semiquinoneimines being somewhat more stable than the semiquinone of hydroquinone. The second step results in a quinoneimine, itself rather unstable:� [structures shown].

�

 

Next, there is a page or so with respect tosuperadditive mixtures with hydroquinone (or its derivatives)

�

 

�Very little other work seems to have been reported on physicochemical investigations of the semiquinoneimine of Metol and allied compounds. Conventional polarography shows a single, two electron step��, etc.

�

 

�Oxidised Metol combines with sulphite as does oxidised hydroquinone, giving a monosulphonate of Metol. This reaction is an essential one in developers in which Metol is the sole developing agent, as certain oxidation products of Metol exhibit a strong inhibiting effect on development. (This is in contrast to the effect of the oxidation products of hydroquinone). The exact mechanism of this reaction with sulphite is still obscure, but the greater reactivity of the semiquinoneimine compared with the quinoneimine suggest the initial reaction is with the former.�

 

[end of my excerpts from Mason]

 

There is more in �The Theory��, but I think it exceeds my ability to clip excerpts. If one of the chemists want to interpret, email me for some snapshots of pages.

[Bill C]

hmmm, all of my apostrophes and quotation marks seem to have turned into garbage characters; they did NOT do this on the preview. Anyone have any ideas why? Also, at the end of various sections, I used three dots (ellipsis?) which also turned into garbage characters.

[Bill C]

hmm, the garbage character issue seems to go back to about the beginning of this year, about the same time I switched to a new machine and IE. But I usually check after posting and I did not notice this problem prior to today. hmm. Maybe it is a browser setting. In the meantime I am avoidng apostrophe and quote characters.

[Bill C]

>> [Jordan] While we're on the subject -- Ron, perhaps you can answer this -- I would love to know what the oxidation product of *phenidone* is.

ﾅ

[Rowland] All of my texts on developers are silent on phenidone which is 1-Phenyl-3-pyrazolidinone.<<

 

I hesitate to start on the phenidone, but both the Metol sources also discuss phenidone. Here is just a bit from [start quote]The Theory of the Photographic Process[end quote].

 

[start quote]Phenidone is oxidized chemically in solution by a one-electron reversible step to form a neutral free radical..[start quote] [ellipsis][start quote]The radical does decay slowly in a second-order irreversible dismutation reaction to form Phenidone and 1-phenyl-3-hydroxypyrazole.[start quote]

 

Jordan, feel free to email me if you want more.

 

 

Test of "in quotes" just to see if it's better.

[Bill C]

Ok, regarding the garbage characters; I normally write my post in MS Word, then copy and paste into this window. With my new machine is a new version of MS Word 2000.

 

The very previous post with "quote test" was done via Notepad; it worked ok, so I guess I will now avoid use of Word for putting these together.

 

I'll also repost my first response thusly!

[Bill C]

* this is a repost with the garbage characters fixe (I hope) *

 

>> [Rowland (Ron)] 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 <<

 

I wasn�t going to bother looking, on the assumption that if Ron didn�t have the info, who would? But today, I got a little free time on my hands and looked around a bit.

 

It turns out that there are brief discussions in both �Photographic Processing Chemistry� (Mason; 1966) and �The Theory of the Photographic Process� (Fourth edition; James, ~1977?).

 

Also, the weather was pretty nice so I took a little walk down to the local library to check their books. They have Mason�s 2nd edition (1975) which seemed to have exactly the same section on metol. Also, they have the THIRD edition of �The Theory of the Photographic Process� (Mees and James; 1966); this did NOT seem to have the pertinent information.

 

Not being a chemist, I won�t try to interpret or explain (I�m afraid Jordan or Ron will catch me on something), but here are a couple exerpts:

 

From Mason,

�Metol is a derivative of para-aminophenol, and most of the reactions described will be characteristic of para-aminophenols in general.�

�

 

Next, some structures are shown with discussion and rough values for K.sub.a and K.sub.b.

�

 

�The oxidation of para-aminophenols can proceed in two one-electron steps, the intermediate semiquinoneimines being somewhat more stable than the semiquinone of hydroquinone. The second step results in a quinoneimine, itself rather unstable:� [structures shown].

�

 

Next, there is a page or so with respect tosuperadditive mixtures with hydroquinone (or its derivatives)

�

 

�Very little other work seems to have been reported on physicochemical investigations of the semiquinoneimine of Metol and allied compounds. Conventional polarography shows a single, two electron step��, etc.

�

 

�Oxidised Metol combines with sulphite as does oxidised hydroquinone, giving a monosulphonate of Metol. This reaction is an essential one in developers in which Metol is the sole developing agent, as certain oxidation products of Metol exhibit a strong inhibiting effect on development. (This is in contrast to the effect of the oxidation products of hydroquinone). The exact mechanism of this reaction with sulphite is still obscure, but the greater reactivity of the semiquinoneimine compared with the quinoneimine suggest the initial reaction is with the former.�

 

[end of my excerpts from Mason]

 

There is more in �The Theory��, but I think it exceeds my ability to clip excerpts. If one of the chemists want to interpret, email me for some snapshots of pages.

[Bill C]

** Sorry, Lex, this is a third try. It looks like Word 2000 used different characters for quotes, etc. I've retyped all those characters in Notepad. Hope this works! **

 

 

>> [Rowland (Ron)] 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 <<

 

I wasn't going to bother looking, on the assumption that if Ron didnﾒt have the info, who would? But today, I got a little free time on my hands and looked around a bit.

 

It turns out that there are brief discussions in both "Photographic Processing Chemistry" (Mason; 1966) and "The Theory of the Photographic Process" (Fourth edition; James, ~1977?).

 

Also, the weather was pretty nice so I took a little walk down to the local library to check their books. They have Mason's 2nd edition (1975) which seemed to have exactly the same section on metol. Also, they have the THIRD edition of "The Theory of the Photographic Process" (Mees and James; 1966); this did NOT seem to have the pertinent information.

 

Not being a chemist, I won't try to interpret or explain (I'm afraid Jordan or Ron will catch me on something), but here are a couple exerpts:

 

From Mason,

"Metol is a derivative of para-aminophenol, and most of the reactions described will be characteristic of para-aminophenols in general."

...

 

Next, some structures are shown with discussion and rough values for K.sub.a and K.sub.b.

...

 

"The oxidation of para-aminophenols can proceed in two one-electron steps, the intermediate semiquinoneimines being somewhat more stable than the semiquinone of hydroquinone. The second step results in a quinoneimine, itself rather unstable:" [structures shown].

...

 

Next, there is a page or so with respect tosuperadditive mixtures with hydroquinone (or its derivatives)

...

 

"Very little other work seems to have been reported on physicochemical investigations of the semiquinoneimine of Metol and allied compounds. Conventional polarography shows a single, two electron stepﾅ", etc.

...

 

"Oxidised Metol combines with sulphite as does oxidised hydroquinone, giving a monosulphonate of Metol. This reaction is an essential one in developers in which Metol is the sole developing agent, as certain oxidation products of Metol exhibit a strong inhibiting effect on development. (This is in contrast to the effect of the oxidation products of hydroquinone). The exact mechanism of this reaction with sulphite is still obscure, but the greater reactivity of the semiquinoneimine compared with the quinoneimine suggest the initial reaction is with the former."

 

[end of my excerpts from Mason]

 

There is more in "The Theoryﾅ", but I think it exceeds my ability to clip excerpts. If one of the chemists want to interpret, email me for some snapshots of pages.

[rowland_mowrey]

Bill;

 

Thanks for the information. I have Mees, but not the Mees and James, nor the Mason. I was over at RIT the other day, but didn't stop at their library. I was in a hurry to get some paper and chemicals at the store.

 

Your note on Metol confirms in detail what my texts say in words. Metol oxidizes in a manner similar to HQ and reacts with sulfite. It does not clarify how powerful a developing agent HQ sulfonate or Metol sulfonate are. I have heard that they are stronger and they are weaker than the parent chemicals. Most reliable data suggest that they are stronger.

 

The reaction of phenidone is new to me but certainly understandable. And, it appears to have no reaction route involving sulfite. Therefore a reaction product is not formed that is a reductant as is HQ sulfonate and (presumably) metol.

 

Thanks for the excellent bit of research. That does a lot of clarification for me.

 

Regards.

 

Ron Mowrey

[lex_jenkins]

Sorry about the garbage characters, folks. It appears that what we have here is failure to communicate. Occasionally photo.net develops hiccups that produce odd reactions. A typical hiccup is for HTML formatting to disappear, leaving only the tags behind, despite the writer having done everything correctly.

 

Just a wild guess, but you might also check the character sets available on your browser and see whether fiddling with any of those options fixes the problem.

[mark_sage]

I have found that a thorough understanding of photochemistry is secondary in importance

to knowing how the appearance of the final print is affected by the inclusion/exclusion

and proportion of the various chemicals within a film developer formula. This is not to say

that an understanding of the chemistry doesn't help in the formulation of hypotheses, but

testing trumps theory. When the criterion is one's aesthetic impression of the final print,

the formulation of developers must, as Ron says, be more art than science.

 

I can say from experience that increasing the level of sulfite (up to a point) increases the

activity of all developer formulas containing metol or p-aminophenol (Rodinal) - I'm

surprised to hear that Haist says otherwise, because it just ain't so. I had assumed (per

Anchell and Troop's comments on D-76) that the silver-solvent properties of the sulfite

increased the accessibility of sensitive sites in the silver crystals, thus increasing the rate

of development. From reading this discussion, it does seem that the sulfite also increases

developer activity by activating the oxidation products of the aminophenol developers. I

believe Anchell and Troop explain this activity as the sulfite retarding the oxidation of the

developing agents during development. However, they are right in the general sense that

the sulfite extends the activity of a given amount of metol.

 

What really interests me about this discussion, and the comments about phenidone, is that

in my experience the inclusion of phenidone (and to a lesser extent hydroquinone) in a

film developer formula has more effect on apparent image definition than the inclusion of

moderate amounts of sulfite. While some believe that the ultimate high-definition film

developer would contain no sulfite, I find the selection of developing agents to just as

important to sharpness as any grain-softening effect of sulfite in moderate concentrations

(below about 40g/L). In fact, because sulfite increases developer activity, increasing

sulfite concentration reduces development times, up to a point, which means that as you

increase the silver-solvent effect of the developer you also decrease the length of time the

film is exposed to the solvent solution. I personally feel that phenidone and hydroquinone

are both undesirable in formulas designed to maximize sharpness. All things considered,

I think neither is a great developer for film (assuming you're only concerned with image

quality). Though the mechanism may be different, it seems that because their oxidation

products do not inhibit development (and in the case of hydropuinone actually increases

developer activity due to increased pH), their inclusion minimizes adjacency effects in a

way which has a similar effect to the combination of metol with higher concentrations of

sulfite. In particular, I believe that in most developers hydroquinone acts to increase

overall contrast at the expense of microcontrast, which is pretty much the opposite of

what I want in a developing formula.

 

Particularly with T-grain films, I feel that the best developers contain ascorbate with metol

or paraminophenol (or both) and a fairly low concentration of Sulfite (10-25g/L). To my

eye, most developers containing hydroquinone or phenidone yield a compromised

impression of detail and/or a cloudy rendering of tonality. If I want a smoother rendition

of tonality I would be more inclined to increase the concentration of sulfite and/or

increase buffering and/or add sodium chloride rather than use either of these developing

agents. Your results may vary.

[jim_appleyard]

Grant, LDS is better.

[eugen_mezei]

On 5/26/2004 at 6:09 AM, tklim said:

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.

I tried to maximise the compensating effect to get non-burned highlights. So I did D23 1+3. Showed some result but not enough. So I did more or less stand development. No improvement.
So the trick is in agitation? That is contraintuitive. What is the explanation?