sbreheny
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Carbon Tetrachloride and Iron -> Ferric Chloride?
Hi all,
I recently was able to obtain a bottle of carbon tetrachloride. It was still sealed despite probably being about 20 years old. When I removed the
plastic shrinkwrap around the plastic cap and unscrewed it, a fair amount of brown debris fell out. Underneath the brown debris was a plastic plug
which seemed to be intact.
The brown debris is mildly attracted to a magnet and it exudes a very staining yellow liquid which is very reminiscent of ferric chloride, which I
have often seen and used as a copper etchant.
I have a bottle of a different reagent from the same company, which was also sealed, and when I removed its cap, there was a steel bottle cap, like a
beer bottle, crimped onto the mouth of the glass bottle. Under the crimped cap was another plastic stopper.
I think that there was originally a steel cap on the CCl4 bottle but it corroded into brown debris. I would normally think that maybe it just rusted
but the yellow liquid is not typical of rust.
Does anyone know if CCl4 will react with iron under normal, benign conditions to form FeCl3? If it does, it is still a bit of a mystery to me how the
CCl4 got out through the intact plastic plug.
Sean
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blogfast25
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Quote: Originally posted by sbreheny  | Does anyone know if CCl4 will react with iron under normal, benign conditions to form FeCl3? If it does, it is still a bit of a mystery to me how the
CCl4 got out through the intact plastic plug.
Sean
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Not at room temperature.
Your yellow liquid may be a bit of low concentration colloidal ferric hydroxide (it has a tendency to peptise). It's also possible that acidic lab
fumes caused the corrosion over years, that could result in part of the iron being solubilised as ferric salts.
One way to find out is to check the liquid for significant presence of chlorides, e.g. using silver nitrate.
[Edited on 22-2-2014 by blogfast25]
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AJKOER
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OK, not Iron but Ferric oxide with time may work as per this partial extract from Atomistry.com on TiCl4 (http://titanium.atomistry.com/titanium_tetrachloride.html ) to quote:
"as well as by leading the vapour of carbon tetrachloride or chloroform over the heated dioxide"
where TiO2 is the referenced dioxide forming TiCl4. Now, replacing Titanium dioxide with Fe2O3 and mild heat (and/or any sunlight) with sufficient
time may behave similarly and is the actual path to the observed FeCl3 formation.
--------------------------------
Actually came across a full text reference "Reductive Dechlorination of Carbon Tetrachloride Using Iron(II) Iron(III) Hydroxide Sulfate (Green Rust)"
at
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&cad=rja&ved=0CE4QFjAI&url=http%3A%2F%2Fwww.researchgate
.net%2Fpublication%2F231291150_Reductive_Dechlorination_of_Carbon_Tetrachloride_Using_Iron(II)_Iron(III)_Hydroxide_Sulfate_(Green_Rust)%2Ffile%2F50463
520a8e505023e.pdf&ei=bukIU7ezMOPhsASk3oLQDg&usg=AFQjCNG75ZbDAZ7dXSw6Q4nCXtEDGZ-BSA where CCl4 is reduced with so called green rust.
Interesting, a mention of the transformation of CCl4 with zero valence iron as well.
[Edited on 22-2-2014 by AJKOER]
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blogfast25
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AJ:
CCl4 (and other chlorinated solvents) have been used as chlorinating agents of metal oxides. It requires high temperatures and isn't relevant to this
simple case.
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AJKOER
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Blogfast:
I would agree with your comment if I haven't read the paper. Here is a partial quote from the first page:
"The reductive dechlorination of CCl4 and CHCl3 in the
presence of the synthetic sulfate form of green rust (GRSO4),
FeII4FeIII2(OH)12SO4yH2O, at pH 8 and room temperature
was investigated. Reduction of CCl4 produces CHCl3 and C2Cl6
as main chloroaliphatic products, while GRSO4 is oxidized
to magnetite (Fe3O4). The formation of C2Cl6 indicates a coupling
reaction between trichloromethyl radicals in the suspension.
...The transformation of CCl4 by GRSO4 can be described by
pseudo-first-order reaction kinetics with respect to formation
of chloride."
Also, with respect to Iron(0), the author states on page 310:
"However, reduction of CCl4 appears to be in the same order
of magnitude for systems containing either iron(0) or iron(II) in GRs. Hitherto,
the role of GRs for reduction of CCl4 when iron(0) comprises
the initial reductant has not been recognized. However, GRs
form as intermediate corrosion products of cast iron (1, 32-
36) and thus also should form where iron(0) is used for
remediation. Green rusts are also expected to form in nonacid
hydromorphic soils, sediments, and landfills which often
contain substantialamountsof iron. In all these environments
GRs may actively participate in the reduction of CCl4."
The cited explanation by the author is also interesting citing a surface interaction. To quote:
"The reaction mechanism between a highly nonpolar
compound such as CCl4 and a polar layered mineral such as
GRSO4 is not completely understood. Reactive sites located
at the GR mineral surface probably initiate the reaction.
Interestingly, the rate of CCl4 reduction observed here is close
to the rates of nitrate reduction by GRSO4 (8). It was found
that nitrate reacted only at outer GRSO4 particle surfaces,
whereas much higher reduction rates could be obtained when
nitrate had access to interlayer positions (9). Carbon tetrachloride
probably cannot penetrate the GR interlayer, as
reduction rates then would be much higher. Increasing the
reactive surface area by decreasing particle sizes or opening
up the GR interlayers by amphiphilic molecules should greatly
enhance the rate of reduction."
The author postulates the following Equations (2) and (3) on page 309:
FeII4FeIII2(OH)12SO4 + CCl4 --> 2Fe3O4 + CHCl3 + Cl- + SO4 2- + 3H+ + 4H2O (2)
FeII4FeIII2(OH)12SO4 + 2CCl4 --> 2Fe3O4 + C2Cl6 + 2Cl- + SO4 2- + 4H+ + 4H2O (3)
I would add, in the current context of Ferric chloride formation, the reaction:
Fe3O4 + 8 HCl --> FeCl2 + 2 FeCl3 + 4 H2O
Also, it is possible for a cast iron bottle cap to contain Sulfur (see Wikipedia http://en.wikipedia.org/wiki/Cast_iron ), which, over time, could be oxidized to sulfate and to the instrumental so called green rust.
[Edited on 23-2-2014 by AJKOER]
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sbreheny
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I have saved most of the brown debris and some of the liquid and when I get a chance I will try testing for chloride ions using silver nitrate as
suggested. Thanks!
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sbreheny
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Hi all,
Well, I finally got a chance to do the test for chloride using silver nitrate. It does look like there are chloride ions in the mystery material.
I took some of the brown debris, ground it up in a mortar, and added distilled water. I then gravity filtered it through Whatman #1 filter paper. The
resulting liquid looked a little cloudy. I let it sit for about 24 hours and it looked no different. I then vacuum filtered it through a much finer
glass fiber filter (1.5 micron size). A little better but still not 100% clear so it looks like there are suspended particles smaller than 1.5
microns. This is the test tube on the left of the attached image. You can see through it to the plastic post behind it but it is a bit cloudy.
The second part of the image, just to the right, is the test tube a few minutes after I added 1 gram of silver nitrate and stirred. It turned milky,
with a tinge of yellow/brown, right away. The third section of the image (next one to the right), is the test tube after about 2 hours. There is a
precipitate but there is still something suspended and it is much more white and much less yellow. The final section to the right is the result after
sitting overnight. Almost clear liquid with a whiteish-brown precipitate.
It occurred to me that there are still multiple reasons why there could be ferric or ferrous chloride in this sample. Another poster here said that
maybe the iron corroded due to exposure to acid fumes in the area where it was stored. If so, those could have been HCl fumes.
Any ideas?
Thanks,
Sean
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blogfast25
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| Quote: Originally posted by sbreheny | It occurred to me that there are still multiple reasons why there could be ferric or ferrous chloride in this sample. Another poster here said that
maybe the iron corroded due to exposure to acid fumes in the area where it was stored. If so, those could have been HCl fumes.
Any ideas?
Thanks,
Sean
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The bottle was quite old, IIRW. Certainly acid fumes could cause gradual corrosion over prolonged periods of time. I think it's a far saner
explanation than direct reaction of iron with CCl4 at RT.
It could also be that the bottle was stored under a fume hood during some synthesis or other. Strong HCl fumes lead very quickly to corrosion of Fe
and Al, even at fairly short exposure times.
If you're worried about the integrity of the CCl4, I wouldn't be.
Tip: when you had trouble filtering, the usual remedy is to pass the filtrate multiple times over the same filter, until it runs clear. Filters,
somewhat paradoxically, really only work well when their pores are partly blocked.
[Edited on 2-3-2014 by blogfast25]
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sbreheny
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| Quote: Originally posted by blogfast25 |
The bottle was quite old, IIRW. Certainly acid fumes could cause gradual corrosion over prolonged periods of time. I think it's a far saner
explanation than direct reaction of iron with CCl4 at RT.
It could also be that the bottle was stored under a fume hood during some synthesis or other. Strong HCl fumes lead very quickly to corrosion of Fe
and Al, even at fairly short exposure times.
If you're worried about the integrity of the CCl4, I wouldn't be.
Tip: when you had trouble filtering, the usual remedy is to pass the filtrate multiple times over the same filter, until it runs clear. Filters,
somewhat paradoxically, really only work well when their pores are partly blocked.
[Edited on 2-3-2014 by blogfast25] |
Thanks, blogfast, I didn't realize that about filtering, I will try that next time I encounter the same problem.
I also agree that HCl or other Chlorine-containing vapors from outside the bottle are the likely culprit.
I also noticed that the top layer of the precipitate turned very dark gray after exposure to daylight through the window this morning, just as you
would expect for silver chloride!
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