Question about home made "Rodinal"

[David Lyga]

I understand that it is possible to make a film developer similar to Rodinal with easily obtained ingredients. Namely, those chemicals are acetaminophen (easily purchased even at the dollar store), sodium sulfite, anhy, and sodium hydroxide (drain cleaner lye).

The standard literature for Rodinal states that no sodium carbonate can be added to Rodinal because doing so will "attack the base", I am not a chemist so I do not really know what that means, but i interpret it to mean "don't do it".

However, isn't sodium hydroxide simply sodium carbonate "on steroids" in that it does the same thing (accelerates the developer) but does it much faster? If so, in rough terms, why is sodium carbonate a "no no" but sodium hydroxide is not only permitted, but NEEDED in the formula.

In common sense terms my question seems eminently rational, but there is something that I am really missing here. Please respond in readily accessible vernacular, in order to placate my undernourished brain. Thank you. - David Lyga

 

[Luckless]

Hopefully someone can expand on what the phrase "attack the base" actually means in this case, as I'm also curious about learning more details on the chemistry we're using.

Is this referring to 'attacking the core of the chemistry we need for photo-development reactions', or does sodium carbonate react with other more alkali entries on the ingredients list to do unhelpful things?

Another point that might be helpful, being able to explain why Na2CO3 [Sodium carbonate] is the less 'aggressive' compound than NaOH [Sodium hydroxide] given that NaOH has less sodium for reactions to play with.

 

[Martin Rickards]

I can't help you much with the specifics but acetominophen (paracetamol) is not the same as para-aminophenol (real Rodinal) and may react differently to different alkalis

 

[Donald Qualls]

In Parodinal, the sodium hydroxide also manages the conversion of n-acetyl-p-aminophenol (paracetamol, acetaminophen) into p-aminophenol (our intended developing agent). Sodium carbonate won't do that job; as I understand it (as a non-chemist) it takes a high enough pH to cleave the acetyl group off the original molecule. Further, sodium carbonate will reduce the activity (by buffering down the pH) and may allow recombination of the acetyl with the p-aminophenol (not sure about that last).

If one wants it badly enough, it ought to be possible (no, I don't know how) to separate out the p-aminophenol from the Parodinal, or produce it with fewer hangers-on, and convert it to n-methyl-p-aminophenol sulfate, aka metol.

 

[Anon Ymous]

I can't help you much with the specifics but acetominophen (paracetamol) is not the same as para-aminophenol (real Rodinal) and may react differently to different alkalis

Paracetamol is converted to p-aminophenol in a process called base hydrolysis using sodium hydroxide. That's what is used in Parodinal.

 

[David Lyga]

In Parodinal, the sodium hydroxide also manages the conversion of n-acetyl-p-aminophenol (paracetamol, acetaminophen) into p-aminophenol (our intended developing agent). Sodium carbonate won't do that job; as I understand it (as a non-chemist) it takes a high enough pH to cleave the acetyl group off the original molecule. Further, sodium carbonate will reduce the activity (by buffering down the pH) and may allow recombination of the acetyl with the p-aminophenol (not sure about that last).

If one wants it badly enough, it ought to be possible (no, I don't know how) to separate out the p-aminophenol from the Parodinal, or produce it with fewer hangers-on, and convert it to n-methyl-p-aminophenol sulfate, aka metol.

I can relate to the carbonate 'reducing' the alkalinity in view of the sodium hydroxide. - David Lyga

 

[BradS]

....isn't sodium hydroxide simply sodium carbonate "on steroids"....

in a very limited sense, I guess that's true but...

They're like totally different molecules, man (think Jeff Bridges' character, The Dude in The Big Lebowski )

I mean, for example, Sodium carbonate has a carbon atom where as Sodium hydroxide has no Carbons...and Sodium hydroxide has a Hydrogen atom!

Just think of the difference between water (H2O) and hydrogen peroxide (H2O2)...chemically the only difference is one oxygen atom...but you'd be in a world of hurt if you drank a liter of hydrogen peroxide.

In a nutshell, and as others have said, the Sodium Hydroxide is doing more than just lowering the PH of the solution. It is actually necessary to convert the available-over-the-counter, slow acting, self administered human poison to a chemical that can be used to develop film (by reducing silver?) .

 

[David Lyga]

in a very limited sense, I guess that's true but...

They're like totally different molecules, man (think Jeff Bridge's character, The Dude in The Big Lebowski )

I mean, for example, Sodium carbonate has a carbon atom where as Sodium hydroxide has no Carbons...and Sodium hydroxide has a Hydrogen atom!

Just think of the difference between water (H2O) and hydrogen peroxide (H2O2)...chemically the only difference is one oxygen atom...but you'd be in a world of hurt if you drank a liter of hydrogen peroxide.

In a nutshell, and as others have said, the Sodium Hydroxide is doing more than just lowering the PH of the solution. It is actually necessary to convert the available-over-the-counter, slow acting, self administered human poison to a chemical that can be used to develop film (by reducing silver?) .

OK, this is exceptionally well defined and I thank you, except for the fact that you should be aware that sodium hydroxide RAISES the pH, not lowers it. -David Lyga

 

[BradS]

OK, this is exceptionally well defined and I thank you, except for the fact that you should be aware that sodium hydroxide RAISES the pH, not lowers it. -David Lyga

Thank you !

 

[Andrew O'Neill]

It's moments like this where I miss PE!

 

[reddesert]

Hopefully someone can expand on what the phrase "attack the base" actually means in this case, as I'm also curious about learning more details on the chemistry we're using.

Is this referring to 'attacking the core of the chemistry we need for photo-development reactions', or does sodium carbonate react with other more alkali entries on the ingredients list to do unhelpful things?

Another point that might be helpful, being able to explain why Na2CO3 [Sodium carbonate] is the less 'aggressive' compound than NaOH [Sodium hydroxide] given that NaOH has less sodium for reactions to play with.

Okay, I am not PE, nor a chemist, but will attempt to explain.

Acids and bases are strong or weak depending on how completely they ionize in water, producing a lot of free H+ or OH- ions (for acid and base respectively). Sodium hydroxide, NaOH, is a strong base because it ionizes completely. Thus NaOH solution alone has a high pH. It's the amount of OH- produced by reactions of the ions with water that makes the alkaline solution, not the amount of sodium.

A weaker acid or base can be used to "buffer" the pH of a solution. This is because it doesn't ionize completely and make hydroxides by reacting with the water, so effectively it has some reserve capacity. If you put a weak base like sodium bicarbonate (NaHCO3) in water, some of the bicarbonate ionizes to make HCO3- ions. But there is some left unionized. (The power of collective bargaining agreements!)

That means that if you put either a little bit of acid or of base into the bicarbonate solution, some of the bicarbonate will react with the newly introduced H+ or OH-, and it will go back to the equilibrium of a weak base. That's buffering. For more technical information, https://en.wikipedia.org/wiki/Buffer_solution and https://en.wikipedia.org/wiki/Buffering_agent

The net effect of this is that if you add a weak base to a strong base, you don't get an even stronger alkalinity. You are likely to get a weak alkaline, unless you overwhelm the buffer by dumping in a lot of strong base, in which case the weak base is irrelevant. Sodium carbonate is stronger than bicarbonate but much weaker than sodium hydroxide (also why sodium carbonate is less caustic and safer to handle). So it does not add to the alkalinity of the NaOH solution and will likely weaken it.

 

[PhotoJim]

But there is some left unionized. (The power of collective bargaining agreements!)

This is the funniest comment I've seen here in years. Thank you for making me laugh out loud.

 

[Alan Johnson]

In Parodinal, the sodium hydroxide also manages the conversion of n-acetyl-p-aminophenol (paracetamol, acetaminophen) into p-aminophenol (our intended developing agent).
If one wants it badly enough, it ought to be possible (no, I don't know how) to separate out the p-aminophenol from the Parodinal, or produce it with fewer hangers-on, and convert it to n-methyl-p-aminophenol sulfate, aka metol.

Adding acid to PaRodinal (Don't try this at home) does produce a precipitate, very likely p-aminophenol.
Making metol from p-aminophenol is a laboratory synthesis job described here:
:https://archive.org/details/methylationpara00wagngoog

 

[Donald Qualls]

Thanks for the link, @Alan Johnson I'll try to wade through it later. What I've gotten down to so far suggests that the commercial method of manufacturing metol is indeed methylation of p-aminophenol, though I doubt they obtain it by clearing acetyl off acetaminophen (rather, I expect acetaminophen is made from p-aminophenol).

 

[David Lyga]

Okay, I am not PE, nor a chemist, but will attempt to explain.

Acids and bases are strong or weak depending on how completely they ionize in water, producing a lot of free H+ or OH- ions (for acid and base respectively). Sodium hydroxide, NaOH, is a strong base because it ionizes completely. Thus NaOH solution alone has a high pH. It's the amount of OH- produced by reactions of the ions with water that makes the alkaline solution, not the amount of sodium.

A weaker acid or base can be used to "buffer" the pH of a solution. This is because it doesn't ionize completely and make hydroxides by reacting with the water, so effectively it has some reserve capacity. If you put a weak base like sodium bicarbonate (NaHCO3) in water, some of the bicarbonate ionizes to make HCO3- ions. But there is some left unionized. (The power of collective bargaining agreements!)

That means that if you put either a little bit of acid or of base into the bicarbonate solution, some of the bicarbonate will react with the newly introduced H+ or OH-, and it will go back to the equilibrium of a weak base. That's buffering. For more technical information, https://en.wikipedia.org/wiki/Buffer_solution and https://en.wikipedia.org/wiki/Buffering_agent

The net effect of this is that if you add a weak base to a strong base, you don't get an even stronger alkalinity. You are likely to get a weak alkaline, unless you overwhelm the buffer by dumping in a lot of strong base, in which case the weak base is irrelevant. Sodium carbonate is stronger than bicarbonate but much weaker than sodium hydroxide (also why sodium carbonate is less caustic and safer to handle). So it does not add to the alkalinity of the NaOH solution and will likely weaken it.

You are beginning to clarify this. However, it has been my observation that adding sodium bicarbonate to a MQ developer with sodium carbonate always slows down the development. Perhaps this is because the baking soda is a weaker form of alkaline than is the sodium carbonate??? Somewhat like sodium carbonate is a weaker form of alkaline than is sodium hydroxide? - David Lyga

 

[BradS]

You are beginning to clarify this. However, it has been my observation that adding sodium bicarbonate to a MQ developer with sodium carbonate always slows down the development. Perhaps this is because the baking soda is a weaker form of alkaline than is the sodium carbonate??? Somewhat like sodium carbonate is a weaker form of alkaline than is sodium hydroxide? - David Lyga

I’m not certain but I think sodium bicarbonate is slightly acidic.

 

[reddesert]

You are beginning to clarify this. However, it has been my observation that adding sodium bicarbonate to a MQ developer with sodium carbonate always slows down the development. Perhaps this is because the baking soda is a weaker form of alkaline than is the sodium carbonate??? Somewhat like sodium carbonate is a weaker form of alkaline than is sodium hydroxide? - David Lyga

Yes, sodium bicarbonate is a significantly weaker base than sodium carbonate, which is somewhat weaker than sodium hydroxide. For example this table: https://www.aqion.de/site/191 Sodium bicarbonate is the same thing as sodium hydrogen carbonate. For solutions of 10 milli-mol per liter, sodium bicarbonate has a pH of 8.22, sodium carbonate has pH of 10.97, sodium hydroxide has pH of 11.95.
(10 milli-mol is 10/1000 of the atomic weight in grams, so 10 milli-mol of sodium carbonate is 1.0 grams.)

pH is logarithmic so a difference of 1 is a factor of 10 in free OH- ions in solution.

 

[Raghu Kuvempunagar]

The standard literature for Rodinal states that no sodium carbonate can be added to Rodinal because doing so will "attack the base"

Older formulas for Rodinal didn't use Tylenol or its key constituent, acetaminophen. They used either p-aminophenol hydrochloride or p-aminophenol free base which is slightly soluble in water (16g of free base in 1l water). To make p-aminophenol free base more soluble in water, it needs to be converted to the more readily soluble p-aminophenolate salt. For the phenolate salt to form, sufficiently high alkalinity is needed, which is provided by potassium/sodium hydroxide. It's the use of hydroxide that increases solubility of p-aminophenol free base from 16g/l to 80g/l in Gainer's EZ Rodinal giving a highly concentrated developer. If you use carbonate in place of hydroxide, you might not be able to get comparable solubility.

All this chemical jugglery is needed only for making a one part concentrated developer stock. If you have access to p-aminophenol free base, you can make a concentrated solution of it in a suitable organic solvent like isopropanol, glycol or TEA. Sulphite and alkali can be added directly to the working solution.

 

[Athiril]

Ive made parodinal several times in the past, and it is similar enough to Rodinal where a difference isn’t noticeable. I often did it with alcohol (methylated spirits, which is denatured ethanol here) extract of the crushed paracetamol tablets and the filtered, dried and weighed to get a clean and clear version. I’ve also used potassium metabisulphite and potassium hydroxide in adjusted amounts to get potassium sulphite (higher solubility) and potassium hydroxide which would be a bit more active in developer.

I’ve also made it with alcohol as above, but not drying it out, by weighing the alcohol and calculating the amount of dissolved paracetamol and mixing the alcohol straight in wth water, sulphite and hydroxide, my parodinal would have a distinct smell. There’s a few ways to go about it.

Depending on how you go about it you may have to calibrate it, because your 1+25 may end up more like a 1+50 equivalent, as your p-aminophenol concentrate can end up lower.

I remember some discussion how original formula was meant to have no hydroxide excess, only remaining p-aminophenol and sulphite, and hydroxide excess is modern formulas etc.

 

[Donald Qualls]

I remember some discussion how original formula was meant to have no hydroxide excess, only remaining p-aminophenol and sulphite, and hydroxide excess is modern formulas etc.

The original method I read (and the one the OP cited) used a form of titration, adding just enough sodium hydroxide (or potassium hydroxide) concentrated solution to fully dissolve the p-aminophenol precipitate. That would be the way to avoid excess hydroxide, which (in my experience with Parodinal) degrades its storage life.

At some point, I may have to start buying p-aminophenol and making actual Rodinal (ca. 1950 version) to get the longer lasting quality.

 

[Nige]

will "attack the base"

As in the other thread on Parodinal, I have been doing some Covid time wasting with my available household ingredients. Whilst developing one film I had left the leader in some Parodinal (my version) and by the time I'd developed my film, the emulsion on the leader had softened and detached itself from the film base. It was swimming on fluid. I wrangled that onto a piece of RC photo paper and let it dry as ART. Another day I purposely did it to the leader (different film) and it did the same. After pushing that around on the film base I let that dry as ART too. It reminded me of a polaroid emulsion lift, however it ended up looking like ART not a negative. I decided I didn't want to progress my ART in that form!

So although it didn't "attack the base", it certainly did a number on the emulsion. Some of my 'properly' developed (ie diluted Parodinal) negs turned out ok although my recipe didn't like being diluted more than about 1:10

 

[Donald Qualls]

Not surprising if Parodinal concentrate took the emulsion off your film. It'll do the same to your skin, if you leave it in contact long enough, and it'll blind you PDQ if you get it in your eye.

 

[alanrockwood]

I am a chemist, so maybe I can say a few words that might help.

First of all, let's tackle the easy part. Sodium hydroxide is a strong base, which means that when it dissolves in water all of the anions (i.e. negative ions) in sodium hydroxide become free OH-. Note the "-" sign in OH-. It's important because it means that OH- is negatively charged. Basically, OH- is, by definition, a base. (How do you like the play on words in the last sentence?) This more or less repeats what some of the other comments have said.

It becomes more interesting when it comes to the carbonate system. There are three parts to the carbonate system. The first is carbonic acid, H2CO3. It is a weak acid, which means that when it dissolves in water some of the molecules break ("dissociate" is the technical term) into H+ and HCO3-. The rest of the H2CO3 molecules stay intact. (Actually, it more like a dance, where at any instant some of the H2CO3 is breaking apart into H+ and HCO3- and some of the H+ and HCO3- is getting back together to form H2CO3. This is called "dynamic equilibrium".)

The next in the carbonate system is bicarbonate, HCO3-. When sodium bicarbonate (NaHCO3) dissolves it releases free bicarbonate into the water. Bicarbonate is "amphoteric", which means that it can act as either an acid or a base. It can react with water to form OH- plus H2CO3, or it can dissociate to form H+ plus CO3--. As it turns out, the reaction to form OH- plus CO3-- tends to predominate, so on balance bicarbonate is considered a weak base.

The third item in the carbonate system is carbonate itself, CO3--. It is a base because it can react with water to form OH- and HCO3-. However, when sodium carbonate dissolves, not all of it reacts to form OH-, so although CO3-- is a base, sodium carbonate is not nearly as strong of a base as sodium hydroxide. It is, however, a stronger base than sodium bicarbonate.

You can make solutions that are intermediate between the items in the carbonate system. For example, you could make a system containing H2CO3 and NaHCO3 by dissolving some baking soda into selzer water. The solution would then contain some H2CO3 and some free bicarbonate ions, HCO3-. This solution will act as a buffer, which means that it tends to resist changes in pH upon the addition of either H+ or OH-. This buffer system helps keep you alive because it is an important one in your blood. If your blood becomes too acidic or too basic then you die. The H2CO3/HCO3- buffer system in your blood helps prevent that from happening.

You can make another buffer by making a solution from sodium carbonate and sodium bicarbonate. The solution will contain both CO3-- and HCO3-. This CO3--/HCO3- buffer is more basic (i.e. has a higher pH) than the first buffer system I mentioned. It is also much less basic (i.e. has a lower pH) than sodium hydroxide.

What happens when you start adding sodium carbonate to a sodium hydroxide solution? As far as pH is concerned, not much will happen.

However, if you add sodium bicarbonate to a solution of sodium hydroxide it gets more interesting. At first the bicarbonate will react with the hydroxide (HO- is hydroxide) to make CO3-- while reducing the amount of OH- in solution. This lowers the pH, i.e. makes the solution more basic.

If you add more bicarbonate to the sodium hydroxide solution you will eventually get to the point where you have neutralized all of the OH-, and you now have a solution of pure sodium carbonate.

If you add even more bicarbonate you will have a solution containing both HCO3- and CO3--. That solution will be a buffer. At first it will have more CO3-- than HCO3-, the pH will be high, and the buffering capacity will be weak, i.e. the ability to resist changes in pH will be weak. If you add enough bicarbonate so that there are equal amounts of CO3-- and HCO3- then the buffering capacity is at it's maximum. Also, the pH of the solution will be at the same value as something called pKa for bicarbonate, which is 10.3. (I am simplifying the discussion because there are other effects, such as "ionic strength" that can shift the values somewhat from their theoretical values through changing something called "activity coefficients".)

If you add more bicarbonate then you will have a solution with more HCO3- than CO3--, and the pH will be lower, and the buffering capacity will be weak. It will, however, still be on the basic side of the pH scale.

Another way to more or less the same end is to add carbonic acid to a solution of sodium hydroxide. You can convert it to a solution that is a mixture of sodium hydroxide and sodium carbonate, and adding even more will make a solution of pure sodium carbonate. Adding even more than that will get to you a mixture of sodium bicarbonate and carbonic acid ( a buffer). Add more carbonic acid and you get a solution of pure sodium bicarbonate. Keep adding carbonic acid and you get a mixture of bicarbonate and carbonic acid (a buffer at a lower pH).

If you add CO2 to water it makes carbonic acid. (There are some subtleties about that I won't discuss here.) Natural air has a little bit of CO2 in it. One consequence of this is that if you leave a solution of sodium hydroxide exposed to air it will eventually be converted to sodium carbonate, with a corresponding drop in pH. (In principle, it could even react further to make sodium bicarbonate.) Therefore, if you make sodium hydroxide solutions you need to keep them capped. Otherwise, you will lose sodium hydroxide by conversion to sodium carbonate and the pH of the solution will drop.

Anyway, shifting gears a bit, if you add an acid to a solution of sodium hydroxide and para aminophenol, you will eventually drop the pH of the solution enough so that the para aminophenol (which is a negative ion in highly basic solution) becomes a neutral molecule. The neutral molecule is less soluble than the ionic form, and you may get precipitation of the para aminophenol. Adding more acid will eventually convert para aminophenol to positive ions, and then it will dissolve again.

 

[Donald Qualls]

I am a chemist, so maybe I can say a few words that might help.

[snip]

Anyway, shifting gears a bit, if you add an acid to a solution of sodium hydroxide and para aminophenol, you will eventually drop the pH of the solution enough so that the para aminophenol (which is a negative ion in highly basic solution) becomes a neutral molecule. The neutral molecule is less soluble than the ionic form, and you may get precipitation of the para aminophenol. Adding more acid will eventually convert para aminophenol to positive ions, and then it will dissolve again.

Which is the exact reverse/other end of what happens in the classic Rodinal production process -- the step where you add the potassium hydroxide solution, a little at a time, until the precipitate just dissolves, and then stop, follows combining p-aminophenol hydrochloride (the hydrochloric acid salt/ester of p-aminophenol) and sodium sulfite in what, at that point, is an acidic solution. Then you'd add the KOH (or NaOH) until you have just enough alkalinity to redissolve the precipitated p-aminophenol -- which leaves you with Rodinal concentrate (ca. 1930s version, IIRC).

 

[David Lyga]

I do have more questions regarding this "do it yourself" Rodinal. First why is it called "PA" Rodinal? Second, why must is be left untouched for 72 hours after mixing and before use? And, today, I bought 24 caplets at the Dollar Tree for $1. Each caplet has 500mg of Acetaminophen PLUS 25mg of Diphenhydramine HCI. Does this second ingredient do anything positive or negative to the Rodinal experiment? - David Lyga