Re: Gallic Acid/Pyrogallic acid ?

eml@gate.net
Thu, 7 Mar 1996 09:47:39 -0500 (EST)

Peter Marshall
>
> In-Reply-To: <Pine.SUN.3.91.960306013511.10812A-100000@panix2.panix.com>
>
> These two are different
>
> Gallic acid = 3,4,5-tri-hydroxybenzoic acid
> Pyrogallol = 1,2,3-trihydroxybenzene (AKA pyro and pyrogallic acid)
>
> Both readily available from chemical suppliers. Pyrogallol is normally in
> fine feathery white crystals. In a chunkier crystal from it used to be
> called pyraxe - there is no chemical difference.
>
> Gallic acid is soluble around 1% in cold water and 33% in boiling.
>
> Pyrogallol is pretty soluble. It also oxidises very rapidly, especially in
> solution, and sodium sulphite is often dissolved in water before adding the
> pyro to prevent this.
>
> While we are on the pyros, should also mention:
> pyrocatechin (1,2-dihydroxybenzene) also used as a developer,
> pyroligneous acid (crude ethanoic acid - acetic acid to the non-chemist),
> pyroxyline - gun cotton or collodion cotton (fun stuff to make and work
> with but please don't try this at home.)
>
> Peter
> petermarshall@cix.compulink.co.uk
>
While on the subject of Pyro and the undesirability of stain in
alternative processes, a derivative, which used to be marketed as
Rubinol comes to mind. It acts exactly like Pyrogallol, but does
not produce a developer stain. I don't have an empirical chemical
formula for it, but one handbook that I have describes it as
"Tertiary Butyl Pyrogallol". I would assume that this means the
substitution of a butyl radical for the H atom on the position 3
OH.

Also, you have hit a soft spot in my heart with the mention of
Pyrocatechin, which I use quite a bit. This material is VASTLY
less toxic than Pyrogallol, according to the material safety
data sheets, and even substantially safer than Hydroquinone.

I use it as a compensating developer with low sulfite, and as
a substitute for Hydroquinonen some developers. It is a developing
agent which has been little exploited in the U.S., but it is
much cheaper than Pyro or Chlor-Hydroquinone, yet has properites
of both and can to a degree substitute for either.

I have not had the chance, and won't have before I move, to find out
if Pyroccatechin is superadditive with Safranin-O dye (a cheaper
replacement for Phenosafranin) in the same manner as is Hydroquinone.
Back in the '30's, someone found that the presence of a small
amount of Phenosafranin greatly accelerated the action of Hydroquinone.
The effect was so strong, in fact that it was possible to completely
eliminate Metol (Elon, Monomethyl Paraminophenol Sulfate) and use
only cheap hydroquinone in developers. It's my hope that this
will work as well with Ortho as well as Para compounds, and that I
can produce a soft-working, rapid, staining developer.

Sorry to go on at such length, but I suggest that anyone who has
not used Catechol read up on it.

Edward M. Lukacs, LRPS
Miami, Florida, USA

-- 


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