Hydroquinone solubility conundrum

[martian bachelor]

I have an old pound of Kodak hydroquinone which I thought I'd use up

some of to mix up a batch of custom developer. Unfortunately it

didn't seem to want to dissolve very well and I'm wondering what's

going on.<P>

 

My chemistry handbook says hydroquinone's solubility is 60gm/liter (at

15°C) but I'm only trying to get 18gm/liter to dissolve at

35+°C, so it shouldn't be a problem.<P>

 

Another reference I have says hydroquinone oxidizes readily in air

(and therefore should be kept in an airtight container - which it has

but for a long time), but doesn't say what it oxidizes into so I can't

check to see if whatever that is isn't very soluble. The stuff

*looks* the same as it ever has: needlely white crystals, very

"fluffy" and of a fairly low density. From filtering the suspension

of what resulted a few days after the crime I'm guessing only about

half or 2/3rds of what I added actually dissolved. At the time there

was already 6gm metol and 36gm sodium sulfite in the ~750ml of

solution; bumping things all the way up to 1000 ml didn't seem to help

clear the solution very much. Nor did keeping it warm and stirring it

alot over several hours, or adding sodium carbonate and potassium

bromide either.<P>

 

Anybody have any ideas as to what experiment I really did here?<P>

[conrad_hoffman]

A quick look at some formulas shows a maximum of about 7g/l of hydroquinone. An exception is D-82 high energy developer with 14g/l, but it's also got wood alcohol in it. My guess is that you can't dissolve that much hydroquinone in the presence of the other chemicals without some additional solvent. It's only a guess, as the D-82 also uses a whopping 52.5g of sulfite and 14g of Metol. It would probably dissolve in pure hot water. I've also got a pound of the stuff that's probably older than I am, and it seems to work fine. What in the world are you making with that much hydroquinone?

[patrick_gainer]

Hydroquinone will get brown with oxidation. I have made 10% solutions of it in alcohol or glycol, glycol being better for long term storage. It is not vary soluble in cold water, but quite soluble in hot water. Perhaps that is why most commercial powder mixes that contain hydroquinone specify 125 F for mixing.

[martian bachelor]

Thanks for the helpful responses. There was a slight error in my original post -- it should be 72gm of sodium sulfite in the mix, not 36gm. I don't think that matters any.<P>

 

I hadn't thought of adding alcohol... The lack of discoloration of the chemical makes me think the stuff is still OK. (If anything it's the metol which is showing a slight tan...) Did anyone check a chem handbook to confirm the 6 parts in 100 solubility value (@15°C) from mine? The solubility at other/higher temps would be nice to have in any event.<P>

 

I wouldn't think the presence of a little metol and some very soluble salt (sulfite) would affect the ability of the hydroquinone to dissolve very much, but I could be wrong.<P>

 

As to what's it all for... it's just designed to be a general purpose (mostly) paper developer, nothing fancy: when diluted 1:5 it should be similar in composition to Dektol 1:2½ -- a bit more metol and a bit less hydroquinone (they're in a 1:3 rather than a more standard 1:4 ratio). Printing 16x20's (from 4x5 negs) has me going through a lot of developer; I prefer a one-shot approach and it takes 24 or 25 ounces minimum just to reasonably cover a piece of paper that large in a standard 17x21 tray.<P>

[chris_waller]

Hydroquinone should dissolve easily in warm water. Try warming the water to 45-50 C.

[rowland_mowrey]

Chris;

 

My handbook says HQ dissolves in 14 parts of water.

 

I have found in practice that it oxidizes rapidly and dissolves slowly, and therefore I always add the other ingredients first such as sodium sulfite and sodium carbonate. This will assist in dissolving the HQ by forming the sodium salt which is more soluable, and by preventing oxidation.

 

Ron Mowrey

[martian bachelor]

A web search turned up several mentions of 7 parts per 100 at 25°C, which seems about right given the value in my handbook.<P>

 

I thought the order of adding the chemicals -- metol, sodium sulfite, hydroquinone, sodium carbonate, potassium bromide -- was standard. But there was plenty of undissolved hydroquinone still floating around by the time the sodium carbonate was all in solution...<P>

 

The problem w/heating the solution at this point and trying to get what I filtered out to dissolve back in is that it turned virtually black on the filter paper as it dried... I think I'll try and weigh it anyway to get a rough idea of what the balance is and therefore how much is actually in the soup. I'm more concerned with reproducability (i.e., being able to make another batch of basically the same thing in the future) than hitting some target formula. Some paper test strips exposed to full room light developed rapidly and to a nice color just slightly on the warm side of neutral, so it's basically doing what I intended.<P>

[martian bachelor]

In case anyone was wondering how it all turned out, my weighing of what I filtered out of the solution came to only about 3 1/2gms. Meaning about 80% of the 18gms went into solution. It certainly *looked* like a lot more didn't.

[patrick_gainer]

The amount of hydroquinone you want to dissolve will do so quite easily if you add about 6.5 grams of sodium hydroxide to the mix. You can in fact make a concentrated PQ stock with 85 grams of sodium sulfite, 18 grams of hydroquinone, 0.5 grams of phenidone and 6.5 grams of sodium hydroxide in enough water to make 500 ml. This solution, diluted 1+50, will develop HP5+ to normal contrast in 8 minutes at 70 F. You can doctor it up many other ways for use on paper. As Ron said, the sodium salt of hydroquinone is formed and that is much more soluble. If you use p-aminophenol in place of hydroquinone, you can leave out the phenidone for developing film. Use it like Rodinal. The solution will keep longer if you add some excess of hydroquinone or p-aminophenol. I believe the way that works is that aerial oxidation causes the pH to rise which converts some of the undissolved stuff to form the sodium salt and dissolve.