accelerator added to MQ

[Gerald C Koch]

I am not so sure about the similar properties. I have found some literature stating this, but it seemed like all the authors copied old data from other books.

It is correct that the Ilford Formulae 3rd Edition gives (in the ID-24 recipe) Adurol and CHQ as two possible ingredients which might be interchanged. Adurol, as it seems, has been used for both, BHQ (Schering) and CHQ (Hauff) (source: Edmund Lowe in "What you want to know about Developers - Fine grain and Otherwise" (Chicago 1939) - I got the really lousy reprint "Made in India" from amazon)

Lowe is the only author where I have been able to find more information on BHQ / CHQ other than the very basics given by Eder. According to Lowe the substances show at least one significant difference:

CHQ
Reduction Potential: 7 - Mol. Wt. 144,5

BHQ
Reduction Potential: 21 - Mol. Wt. 189

So this suggests that the two substances will show different behavior of some kind.

I believe that I have seen this table and what is given are relative potentials (unitless) what are called bromide potentials rather than actual ones which would be given in mV. A bromide potential is the relative resistance of a developing agent to bromide concentration. Hydroquine is arbitrarily set at 1. Thus BHQ has 3 times the resistance to bromide than does CHQ. Anyway I though it worth a try.

 

[Gerald C Koch]

Champlin used CHQ is two of his formulations #16 and #17. Lowe mentions #16 in his book. It is the only one that Lowe considered worthwhile.

 

[RauschenOderKorn]

Some companies that claim to use Cl-HQ claim that they made it in-situ by adding HCl to Quinone. Well, this can only work in the absence of Oxygen. Even then it is claimed that the oxidation can be restrained by Sulfite. In the end you get either the results I've attached or you get HQMS (Hydroquinone Monosulfonate). The synthesis of Cl-HQ is actually difficult and expensive requiring the addition of Chlorine gas to Qinone in Benzene at high temperature and pressure. It is difficult to purify even then and samples that I have heard of were not pure due to decomposition.

I'm wondering if what people thought was Cl-HQ was really something else and I'm wondering what benefit they expected.

PE

The reaction you are describing is similar to the following source (sorry, in German):

https://books.google.de/books?id=7o...6AEIQDAH#v=onepage&q=Chlorhydroquinon&f=false

If I read this the right way, you can have two different main reactions when adding concentrated HCL to Quinol:
The first: 2 Quinol + 2 HCL -> 2 CHQ
The second: 2 Quinol +2 HCL -> 1 CCHQ + 1 HQ

plus any secondary reaction which might take place.

According to this source, what happens depends "on the circumstances", not describing these circumstances any further. Both reactions produce a developing agent, therefore - as long as proprietary developers are concerned - it worked in some way. But reproduction of these results seems impossible.

 

[Alan Johnson]

LP Clerc Photography Theory and Practice 2nd ed 1946 p240:
The monochlor and monobrom derivatives of hydroquinone are much more energetic developers than hydroquinone itself, especially the bromine derivative, the reduction potential of which is somewhat greater than that of metol. Both forms are known under the trade name Adurol; they are less oxidizable than hydroquinone and give purer blacks.

 

[RauschenOderKorn]

Anyway I though it worth a try.

+1, I totally agree.

 

[Gerald C Koch]

Here is the list of bromide potentials that I have in my motes.

p-Phenylenediamine 0.3
Hydroquinone 1.0
Glycin 1.6
p-Aminophenol 6
Chlorohydroquinone 7
Catechol 7
Dibromohydroquinone 8
Dichlorohydroquinone 11
Pyrogallol 16
Bromohydroquinone 20
Metol 20
Amidol 20 - 40

 

[Photo Engineer]

It was also used as a plate / film developer, CHQ being the only developing agent (or whatever the companies had synthesized believing it was CHQ).
Check out the Lowe book, there you can find some more data.

I have read many many texts. I did not say it was not used, I said it was rather rare compared to others, and actually might be in texts under proprietary names. It is high activity and low fog, and forms brown to red images, but it is hard to make and hard to get pure. There are substitutes, and most companies have stopped using it.

I don't see any comeback on the horizon.

Oh, and see the synthetic flow chart I posted above. This is a likely sequence of events.

PE

 

[Ian Grant]

Chlorquinol's main use was in warm tone developers particularly those used at high dilutions and longer exposure times ie ID24. Older warm tone papers could give rich red tones purely by development but most of these papers contained Cadmium and disappeared by the early 1990s. Chlorquinol was ideal because of it's increased activity compared to Hydroquinone.

When Ilford say Chlorqinol (or Adurol) they are referring to the Hauff brnded Chloroquinol)

Ian

 

[Rudeofus]

According to this source, what happens depends "on the circumstances", not describing these circumstances any further. Both reactions produce a developing agent, therefore - as long as proprietary developers are concerned - it worked in some way. But reproduction of these results seems impossible.

While Sigma Aldrich may not be overly supportive to photographic amateurs, they do know how to source chemistry, even if it has some incredulous structure and costs >1000€ per gram. If Sigma Aldrich can't provide Chlorohydroquinone in better than 80% purity, we can safely assume that it is exceedingly difficult to do so, at least at price point which we are willing to accept. Which brings me to my second point: we can safely assume, that previous generations of photographic craftsmen didn't have access to 99.9% Chlorohydroquinone either, so whatever these folks Lowe, Champlin used, was probably some mixture of Chlorohydroquinone and a whole host of other compounds.

 

[Rudeofus]

LP Clerc Photography Theory and Practice 2nd ed 1946 p240:
The monochlor and monobrom derivatives of hydroquinone are much more energetic developers than hydroquinone itself, especially the bromine derivative, the reduction potential of which is somewhat greater than that of metol. Both forms are known under the trade name Adurol; they are less oxidizable than hydroquinone and give purer blacks.

Having a greater reduction potential at a given pH does not automatically give us a better development agent. The statement "gives purer blacks" is also barely quantifiable, and may not be applicable to modern photographic materials.

I am very cautious about claims of vast superiority of some odd development agents, especially if these claims predate the adoption of Phenidone in photographic developers. Kodak, Fuji, Agfa and Ilford investigated much stranger development agents, and would certainly not have overlooked Chlorohydroquinone if it had any real promise.

 

[Alan Johnson]

Yes, chlorhydroquinone was in the 1937 Ilford formula book in ID 23 but omitted from the 1953 book.

 

[RauschenOderKorn]

we can safely assume, that previous generations of photographic craftsmen didn't have access to 99.9% Chlorohydroquinone either, so whatever these folks Lowe, Champlin used, was probably some mixture of Chlorohydroquinone and a whole host of other compounds.

I do share this assumption, but it would require some investigation to confirm how the CHQ was produced in the 1930s - 1950s. But anyway, with modern emulsions this will not a magic bullet either. The industry dropped CHQ for a reason, although this reason very well might be of some economic nature rather than aesthetics.

My idea (unfortunately not supported by S-A) was just giving it a try at whatever quality is available. I know I might be able to get CHQ from other sources (or play it the S-A way), but actually I decided to try Polychrome Development as described by Wolfgang Moersch instead (homebrew, not the kit he´s selling). This gives "pure blacks" (got that part working) and should show a deep brown tone (not working yet) without the hassle of CHQ.

 

[Gerald C Koch]

One wonders why CHQ is so expensive as it is a simple molecule. As with many organic chemicals there is more than one starting material for synthesis. One could start with hydroquinone or 2-chlorophenol.

The initial synthesis of azulene an isomer of naphthalene C10H8 required over 50 steps. Both rings had to be built from scratch carbon atom by carbon atom!