A Photography forum. PhotoBanter.com

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » PhotoBanter.com forum » General Photography » In The Darkroom
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Chelating agent for copper (II) in acidic media



 
 
Thread Tools Display Modes
  #1  
Old November 7th 04, 01:20 PM
external usenet poster
 
Posts: n/a
Default Chelating agent for copper (II) in acidic media

Hello,

I'm looking for a chelating agent, which binds to copper (II) in acidic
media with pH somewhere in the range 1 ... 2. I know of a few chelating
agents for copper (II), but they all tend to be most effective at the
basic side of the pH range.

Does anyone of you know of a chelating agent, suitable for such low pH?
As an added constraint I want to mention, that this compound must be
available for the public at reasonable price. Hence, it should not be
very toxic, unstable, air sensitive, etc.

I intend to use it as part of a photographic toner solution.
Thanks,

Wilco

  #4  
Old November 7th 04, 07:29 PM
external usenet poster
 
Posts: n/a
Default


wrote:
Wilco,
The best chelating agent for copper is EDTA
(ethylenediaminetetraaacteic acid whose di-sodium salt is usually

used.
The best pH for copper chelation is around 2.0. Once the complex is
formed at this pH it is stable in highly alkaline and acidic media.
EDTA is stable, perhaps easily available, non-toxic and stable with
respect to air-oxidation.



Farooq,

I actually have some EDTA-Na2 and EDTA-Na4. Both of these perfectly
chelate with copper (II), but as soon as a few drops of 1 M H2SO4 are
added, then the chelate is destroyed. I tried this, by mixing a
solution of CuSO4 and K3Fe(CN)6. Without EDTA this mixture gives a
precipitate. With EDTA (either -Na4 or -Na2) the solution remains
clear. However, when the solution is somewhat acidified, then a
precipitate is formed again.
One can also see that the complex is destroyed without the
ferricyanide. The complex has a deep blue color. On acidification with
even a small amount of H2SO4, the deep blue color disappears and the
color of plain aqueous Cu(2+) appears again.

As you write, the complex should be stable. Did I miss something?
Should the complex be prepared in a special way? Is the blue complex I
have not the same as what you are referring to?

What I want is that Cu(2+), [VO2](+) and [Fe(CN)6](3-) all are in
solution at the same time. The pervanadyl only can exist at low pH. I
can have the pervanadyl and ferricyanide in solution at the some time,
but adding the copper is a problem. When I manage to have all these
three in solution, I probably would have created a bright orange toner,
which is quite special in photography. If you are interested in this
aspect of chemistry, the idea behind metal-ferricyanide toning is
explained in

http://www.woelen.nl/photo/toner.pdf

which I wrote approximately half a year ago. The second part of this
document may be most interesting for you.

Wilco

  #5  
Old November 8th 04, 01:09 AM
Uncle Al
external usenet poster
 
Posts: n/a
Default

wrote:

wrote:
Wilco,
The best chelating agent for copper is EDTA
(ethylenediaminetetraaacteic acid whose di-sodium salt is usually

used.
The best pH for copper chelation is around 2.0. Once the complex is
formed at this pH it is stable in highly alkaline and acidic media.
EDTA is stable, perhaps easily available, non-toxic and stable with
respect to air-oxidation.


Farooq,

I actually have some EDTA-Na2 and EDTA-Na4. Both of these perfectly
chelate with copper (II), but as soon as a few drops of 1 M H2SO4 are
added, then the chelate is destroyed. I tried this, by mixing a
solution of CuSO4 and K3Fe(CN)6. Without EDTA this mixture gives a
precipitate. With EDTA (either -Na4 or -Na2) the solution remains
clear. However, when the solution is somewhat acidified, then a
precipitate is formed again.
One can also see that the complex is destroyed without the
ferricyanide. The complex has a deep blue color. On acidification with
even a small amount of H2SO4, the deep blue color disappears and the
color of plain aqueous Cu(2+) appears again.

As you write, the complex should be stable. Did I miss something?
Should the complex be prepared in a special way? Is the blue complex I
have not the same as what you are referring to?

What I want is that Cu(2+), [VO2](+) and [Fe(CN)6](3-) all are in
solution at the same time. The pervanadyl only can exist at low pH. I
can have the pervanadyl and ferricyanide in solution at the some time,
but adding the copper is a problem. When I manage to have all these
three in solution, I probably would have created a bright orange toner,
which is quite special in photography. If you are interested in this
aspect of chemistry, the idea behind metal-ferricyanide toning is
explained in

http://www.woelen.nl/photo/toner.pdf

which I wrote approximately half a year ago. The second part of this
document may be most interesting for you.


You need a hard base that sticks around at low pH without reducing the
copper. Cu(II) is substitution labile. Nitrate isn't much of a
grabber. What about hydroxamic acids (react esters with hydroxylamine
to displace the alcohol)? Dimethyl tartrate is available, and the
extra hydroxyls confer water solubility.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
  #6  
Old November 8th 04, 01:09 AM
Uncle Al
external usenet poster
 
Posts: n/a
Default

wrote:

wrote:
Wilco,
The best chelating agent for copper is EDTA
(ethylenediaminetetraaacteic acid whose di-sodium salt is usually

used.
The best pH for copper chelation is around 2.0. Once the complex is
formed at this pH it is stable in highly alkaline and acidic media.
EDTA is stable, perhaps easily available, non-toxic and stable with
respect to air-oxidation.


Farooq,

I actually have some EDTA-Na2 and EDTA-Na4. Both of these perfectly
chelate with copper (II), but as soon as a few drops of 1 M H2SO4 are
added, then the chelate is destroyed. I tried this, by mixing a
solution of CuSO4 and K3Fe(CN)6. Without EDTA this mixture gives a
precipitate. With EDTA (either -Na4 or -Na2) the solution remains
clear. However, when the solution is somewhat acidified, then a
precipitate is formed again.
One can also see that the complex is destroyed without the
ferricyanide. The complex has a deep blue color. On acidification with
even a small amount of H2SO4, the deep blue color disappears and the
color of plain aqueous Cu(2+) appears again.

As you write, the complex should be stable. Did I miss something?
Should the complex be prepared in a special way? Is the blue complex I
have not the same as what you are referring to?

What I want is that Cu(2+), [VO2](+) and [Fe(CN)6](3-) all are in
solution at the same time. The pervanadyl only can exist at low pH. I
can have the pervanadyl and ferricyanide in solution at the some time,
but adding the copper is a problem. When I manage to have all these
three in solution, I probably would have created a bright orange toner,
which is quite special in photography. If you are interested in this
aspect of chemistry, the idea behind metal-ferricyanide toning is
explained in

http://www.woelen.nl/photo/toner.pdf

which I wrote approximately half a year ago. The second part of this
document may be most interesting for you.


You need a hard base that sticks around at low pH without reducing the
copper. Cu(II) is substitution labile. Nitrate isn't much of a
grabber. What about hydroxamic acids (react esters with hydroxylamine
to displace the alcohol)? Dimethyl tartrate is available, and the
extra hydroxyls confer water solubility.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
  #7  
Old November 8th 04, 01:09 AM
Uncle Al
external usenet poster
 
Posts: n/a
Default

wrote:

wrote:
Wilco,
The best chelating agent for copper is EDTA
(ethylenediaminetetraaacteic acid whose di-sodium salt is usually

used.
The best pH for copper chelation is around 2.0. Once the complex is
formed at this pH it is stable in highly alkaline and acidic media.
EDTA is stable, perhaps easily available, non-toxic and stable with
respect to air-oxidation.


Farooq,

I actually have some EDTA-Na2 and EDTA-Na4. Both of these perfectly
chelate with copper (II), but as soon as a few drops of 1 M H2SO4 are
added, then the chelate is destroyed. I tried this, by mixing a
solution of CuSO4 and K3Fe(CN)6. Without EDTA this mixture gives a
precipitate. With EDTA (either -Na4 or -Na2) the solution remains
clear. However, when the solution is somewhat acidified, then a
precipitate is formed again.
One can also see that the complex is destroyed without the
ferricyanide. The complex has a deep blue color. On acidification with
even a small amount of H2SO4, the deep blue color disappears and the
color of plain aqueous Cu(2+) appears again.

As you write, the complex should be stable. Did I miss something?
Should the complex be prepared in a special way? Is the blue complex I
have not the same as what you are referring to?

What I want is that Cu(2+), [VO2](+) and [Fe(CN)6](3-) all are in
solution at the same time. The pervanadyl only can exist at low pH. I
can have the pervanadyl and ferricyanide in solution at the some time,
but adding the copper is a problem. When I manage to have all these
three in solution, I probably would have created a bright orange toner,
which is quite special in photography. If you are interested in this
aspect of chemistry, the idea behind metal-ferricyanide toning is
explained in

http://www.woelen.nl/photo/toner.pdf

which I wrote approximately half a year ago. The second part of this
document may be most interesting for you.


You need a hard base that sticks around at low pH without reducing the
copper. Cu(II) is substitution labile. Nitrate isn't much of a
grabber. What about hydroxamic acids (react esters with hydroxylamine
to displace the alcohol)? Dimethyl tartrate is available, and the
extra hydroxyls confer water solubility.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
  #8  
Old November 8th 04, 12:00 PM
external usenet poster
 
Posts: n/a
Default


wrote:
wrote:
Wilco,
The best chelating agent for copper is EDTA
(ethylenediaminetetraaacteic acid whose di-sodium salt is usually

used.
The best pH for copper chelation is around 2.0. Once the complex is
formed at this pH it is stable in highly alkaline and acidic media.
EDTA is stable, perhaps easily available, non-toxic and stable with
respect to air-oxidation.



Farooq,

I actually have some EDTA-Na2 and EDTA-Na4. Both of these perfectly
chelate with copper (II), but as soon as a few drops of 1 M H2SO4 are
added, then the chelate is destroyed. I tried this, by mixing a
solution of CuSO4 and K3Fe(CN)6. Without EDTA this mixture gives a
precipitate. With EDTA (either -Na4 or -Na2) the solution remains
clear. However, when the solution is somewhat acidified, then a
precipitate is formed again.
One can also see that the complex is destroyed without the
ferricyanide. The complex has a deep blue color. On acidification

with
even a small amount of H2SO4, the deep blue color disappears and the
color of plain aqueous Cu(2+) appears again.

As you write, the complex should be stable. Did I miss something?
Should the complex be prepared in a special way? Is the blue complex

I
have not the same as what you are referring to?


Copper does form a precipitate with [Fe(CN)6](3-). Doesn't the
ferricyanide ion decompose in highly acidic medium to HCN? Na4EDTA is
very alkaline, but using disodium salt is better. Dissolving H4EDTA is
frustating.

I don't think here is a specific requirement for the preparation of its
EDTA complex. Admittedly, I never went below the pH of 2(which is
failry acidic) for the preparation of copper-EDTA , but once the
complex is prepared you can increase the pH to 12 without any signs of
precipitation, even the blue color is not destroyed. Below the
recommended pH of 2, the complex doesn't form at all because EDTA, then
exists totally in protoned form, the six binding sites are "blocked" by
H.

Another thing that might be relevant to your problem is copper-bromo
complex, add few drops of ammonium bromide in a copper solution
acidified with HCl (ie at very low pH~1), the solution becomes
violet...a qualitative test for copper.
There are many organic complexing reagents for copper but most of them
are used in gravimetric analysis, ie the complexes are highly
insoluble. Copper-tartarate requires alkaline medium and perhaps
citrate too.


What I want is that Cu(2+), [VO2](+) and [Fe(CN)6](3-) all are in
solution at the same time. The pervanadyl only can exist at low pH. I
can have the pervanadyl and ferricyanide in solution at the some

time,
but adding the copper is a problem.


I don't know whether Cu-EDTA, pervanadyl ion and ferricyanide can
coexist together. If by chance a better chelating agent is found it
must have very low affinity for vanadium and iron.

Is pervanadyl ion a true peroxy compound- I guess it should be
[VO2](3+), assuming V(+5).

When I manage to have all these
three in solution, I probably would have created a bright orange

toner,
which is quite special in photography. If you are interested in this
aspect of chemistry, the idea behind metal-ferricyanide toning is
explained in

http://www.woelen.nl/photo/toner.pdf

Very well written.


which I wrote approximately half a year ago. The second part of this
document may be most interesting for you.

Wilco


  #9  
Old November 8th 04, 08:01 PM
Muhammar
external usenet poster
 
Posts: n/a
Default

I would recommend trying L-cysteine hydrochloride hydrate (or
L-cysteine; it is the same thing). It is reasonably cheap and nontoxic
- edible. The only disadvantage is that while the stuff is stable as a
solid, the aqueous solutions have to be stored in fridge to slow down
the air oxidation. Oxidized cysteine solution can develop precipitate.
If you add some antioxidant (ascorbic acid!), the solution will keep
longer.

[Also, try to sell your cysteine/ascorbic photo solution to a
nutrition supplement stores as well - the body builders will quaff it
down by a pint]

wrote in message roups.com...
wrote:
Wilco,
The best chelating agent for copper is EDTA
(ethylenediaminetetraaacteic acid whose di-sodium salt is usually

used.
The best pH for copper chelation is around 2.0. Once the complex is
formed at this pH it is stable in highly alkaline and acidic media.
EDTA is stable, perhaps easily available, non-toxic and stable with
respect to air-oxidation.



Farooq,

I actually have some EDTA-Na2 and EDTA-Na4. Both of these perfectly
chelate with copper (II), but as soon as a few drops of 1 M H2SO4 are
added, then the chelate is destroyed. I tried this, by mixing a
solution of CuSO4 and K3Fe(CN)6. Without EDTA this mixture gives a
precipitate. With EDTA (either -Na4 or -Na2) the solution remains
clear. However, when the solution is somewhat acidified, then a
precipitate is formed again.
One can also see that the complex is destroyed without the
ferricyanide. The complex has a deep blue color. On acidification with
even a small amount of H2SO4, the deep blue color disappears and the
color of plain aqueous Cu(2+) appears again.

As you write, the complex should be stable. Did I miss something?
Should the complex be prepared in a special way? Is the blue complex I
have not the same as what you are referring to?

What I want is that Cu(2+), [VO2](+) and [Fe(CN)6](3-) all are in
solution at the same time. The pervanadyl only can exist at low pH. I
can have the pervanadyl and ferricyanide in solution at the some time,
but adding the copper is a problem. When I manage to have all these
three in solution, I probably would have created a bright orange toner,
which is quite special in photography. If you are interested in this
aspect of chemistry, the idea behind metal-ferricyanide toning is
explained in

http://www.woelen.nl/photo/toner.pdf

which I wrote approximately half a year ago. The second part of this
document may be most interesting for you.

Wilco

  #10  
Old November 8th 04, 08:49 PM
external usenet poster
 
Posts: n/a
Default


Muhammar wrote:
I would recommend trying L-cysteine hydrochloride hydrate (or
L-cysteine; it is the same thing). It is reasonably cheap and

nontoxic
- edible. The only disadvantage is that while the stuff is stable as

a
solid, the aqueous solutions have to be stored in fridge to slow down
the air oxidation. Oxidized cysteine solution can develop

precipitate.
If you add some antioxidant (ascorbic acid!), the solution will keep
longer.

This sounds good. Storage is no problem, because the solutions are not
stored. They are prepared, just before use and then they are discarded.
I only wonder if L-cysteine withstands the oxidizing power of copper
(II) or [VO2](+). The latter is a fairly strong oxidizer with a redox
potential (for V(+5) to V(+4) at pH=0) equal to 1.0 V. Using ascorbic
acid as antioxidant does not work, this reduces copper (II) to
copper(I) at once and the pervanadyl is reduced to blue vanadyl
immediately.


[Also, try to sell your cysteine/ascorbic photo solution to a
nutrition supplement stores as well - the body builders will quaff it
down by a pint]

I also have a bottle containing some nice blue VOSO4.xH2O, the ideal
stuff for bodybuilders... I, however, prefer to keep my health :-)

 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
on this page film wins Developwebsites Digital Photography 142 September 15th 04 06:39 PM


All times are GMT +1. The time now is 08:51 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 PhotoBanter.com.
The comments are property of their posters.