Endimion17
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Complex compound synthesis procedures dump site
Judging by the search tool, it seems these procedures are scarce and dispersed, so I thought it would be cool to have a place for dumping the
preparative procedures for all to see.
Complex compounds are usually easy to prepare if you have the proper ingredients. There's usually some mixing, precipitating and filtering involved,
and the products can be a real eye candy.
I'll start with an example, and I encourage others to join. However, it would be nice if you used UPPERCASE BOLD when starting with
the procedure, to point it out visually.
Also, one post per procedure is a good way to avoid cluttering.
And now onto the procedures...
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Endimion17
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SYNTHESIS OF POTASSIUM TRISOXALATOFERRATE(III) TRIHYDRATE
K<sub>3</sub>[Fe(C<sub>2</sub>O<sub>4</sub> <sub>3</sub>]×3H<sub>2</sub>O
equipment:
- two beakers (100, 250 cm<sup>3</sup>
- small graduated cyllinder or a pipette with 0.1 cm<sup>3</sup> precision
- Büchner funnel with filter paper, hooked up to a Büchner flask
- vacuum pump with rubber tubing
- thermometer (-10 °C - 150 °C or similar)
- glass rod
chemicals:
- Mohr salt
- sulphuric acid, 2 mol dm<sup>-3</sup>
- aqueous solution of oxalic acid dihydrate, 10%
- potassium oxalate monohydrate
- ethanol, conc.
- distilled water
- acetone
- hydrogen peroxide, 20%
procedure:
Dissolve 2 g of Mohr's salt in 7 cm<sup>3</sup> of hot distilled water acidified with ~0.35 cm<sup>3</sup> of 2 M sulphuric
acid.
Add 9.8 cm<sup>3</sup> of oxalic acid solution. Heat carefully to the boiling point. Stop the heating and wait for the yellow iron(II)
oxalate to settle down. Decant the water and add 7 cm<sup>3</sup> of hot distilled water. Mix thoroughly and repeat the decanting.
Prepare a hot aqueous solution of potassium oxalate monohydrate (put 1.3 g of the salt in 4.5 cm<sup>3</sup> of water).
Add it to the iron(II) oxalate precipitate and mix the suspension.
Slowly add 4 cm<sup>3</sup> of hydrogen peroxide drop by drop while mixing with a thermometer, ensuring the temperature doesn't exceed 40
°C.
After that, heat to the boiling point and add 2.6 cm<sup>3</sup> of the oxalic acid solution. The precipitate should dissolve.
Add 0.7 cm<sup>3</sup> more, drop by drop, while maintaining the temperature close to the boiling point.
Filter the hot solution and let it cool down.
Start adding 5 cm<sup>3</sup> of ethanol, drop by drop. If crystals do not form, reduce the volume by boiling in the dark or leave it in
the dark for several days.
Filter off the crystals using a Büchner funnel and wash them with a 1:1 solution of ethanol and water. Repeat the washing using acetone.
Store it at a dark place (black plastic bottle).
reactions involved:
Fe<sup>2+</sup> + C<sub>2</sub>O<sub>4</sub><sup>2-</sup> ->
FeC<sub>2</sub>O<sub>4(s)</sub>
2FeC<sub>2</sub>O<sub>4(s)</sub> + 6K<sup>+</sup> +
4C<sub>2</sub>O<sub>4</sub><sup>2-</sup> + H<sub>2</sub>O<sub>2(l)</sub>
+2H<sup>+</sup> + H<sub>2</sub>O -> 2K<sub>3</sub>[Fe(C<sub>2</sub>O<sub>4</sub><sub>3</sub>]×3H<sub>2</sub>O<sub>(s)</sub>
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bbartlog
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Not sure I understand. In general, if you have performed an interesting synthesis, you should put it in the Prepublication thread (if you are willing
to do a good writeup) or just some thread devoted to that compound (otherwise). If you've just found a description of an interesting synthesis that is
online somewhere, you can link it for discussion... but generally I would think that absent something interesting to say or some intent to do the
synthesis, it doesn't make much sense to just paste it here. Now, if you have a procedure from some book or paper that *isn't* available online, that
would actually make sense to put here. But the example compound you've chosen is not a particularly obscure synthesis, rather it appears to be a
common lab exercise at the university level, so... why?
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blogfast25
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Quote: Originally posted by bbartlog  | | Not sure I understand. In general, if you have performed an interesting synthesis, you should put it in the Prepublication thread (if you are willing
to do a good writeup) or just some thread devoted to that compound (otherwise). |
I agree. Specific threads on intresting systhesis (whether found or tried and tested) are of much greater value than generic threads about
'interesting compounds'.
I don't know if there is an existing thread on the potassium ferric oxalate complex on SM but there is a very detailed uni procedure available on the
net. I can't remember the site but I found it searching for K3Fe(CN)6. If your method is based on an existing text then please provide a reference to
it.
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Endimion17
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bbartlog, it's just one of the many syntheses. Do you know a place on the Web where lots of these syntheses are systematically brought together?
I don't. I know where to find such info, but it's scattered, so I've thought it would be good to have one dumping place at a place where lots of home
chemists wander around.
Some people never even heard of some complex compounds, and this might spark some interest in the subject.
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Endimion17
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SYNTHESIS OF POTASSIUM TETRAPEROXOCHROMATE(V)
equipment:
- Erlenmeyer flask, 100 cm<sup>3</sup>
- small graduated cyllinder
- water-ice bath
- beaker, 100 cm<sup>3</sup>
- glass rod
- Büchner vacuum filtration set
- watchglass
chemicals:
- hydrogen peroxide, 30%
- aqueous solution of potassium hydroxide, 25%
- potassium chromate
- ethanol, conc.
- distilled water
procedure:
Fill the flask with 10 cm<sup>3</sup> of water and the equal volume of potassium hydroxide solution.
Add 2.5 g of finely ground potassium chromate. Mix thoroughly.
Drop by drop, add ~15 cm<sup>3</sup> of hydrogen peroxide and don't stop mixing. The reaction mixture froths with oxygen. Ensure the
reaction temperature doesn't get over 40 °C.
The yellow solution should turn dark brown.
If it doesn't, add likewise 10-15 cm<sup>3</sup> of the peroxide and keep the temperature above room temperature but below 40 °C. Cooling
it down will reduce the reaction rate.
Let it settle and cool down for 5 hours at room temperature.
Filter off the crystals, wash them with ethanol and let them dry on a piece of filter paper.
In case you spot any nonreacted pieces of yellow potassium chromate, wash the product with a small amount of ice cold water, and then with ethanol.
reactions involved:
2K<sub>2</sub>CrO<sub>4(s)</sub> + 2K<sup>+</sup> + 2OH<sup>-</sup> +
9H<sub>2</sub>O<sub>2(l)</sub> -> 2K<sub>3</sub>[Cr(O<sub>2</sub><sub>4</sub>]<sub>(s)</sub> +
10H<sub>2</sub>O<sub>(l)</sub> + O<sub>2(g)</sub>
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Neil
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| Quote: Originally posted by Endimion17 | bbartlog, it's just one of the many syntheses. Do you know a place on the Web where lots of these syntheses are systematically brought together?
I don't. |
I do
http://library.sciencemadness.org/library/index.html
People aren't likely to read through a thread filled with random (sources-less?) synthesis for the same reason that people never bother to read blocks
of texts in posts where the poster has written up a reply or question in the form of a massive uninterrupted block of textual monotony. Individual
threads with meaningful discussion provide a means of agglomerating large amounts of data under a filing system which enables the discussion of each
topic without creating a situation where excessive research digging is needed.
Further to that end, an individual thread with ensuring discussion and sources provides reason for the manufacture of different chemicals where as a
thread of synths without meaning is a bit like hoveland's spam threads of random reactions... that is to say, it is just random...
If you are going to go through all the effort or typing them up, then why not go a bit further and add sources and get them popped into the
publication forum?
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Endimion17
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Well, I do have the sources and references, as I'm actually translating and copying the stuff from some old books.
I've got a ton of this stuff here. Inorganics and organics.
It would be useless to scan them because they aren't written in English.
My intention was not to put online everything I have, but complex salts only. Maybe some organics in the future, too.
I disagree with the statement that people wouldn't check it out. For example, I do that. If I see a nice set of experiments and have the time, I get
down on them. Few days later, my shelf has few compounds more, and my lab book has less empty pages.
So what do I actually have to do?
[Edited on 15-10-2011 by Endimion17]
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Nicodem
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| Quote: Originally posted by Endimion17 | Well, I do have the sources and references, as I'm actually translating and copying the stuff from some old books.
...
So what do I actually have to do? |
The answer is quite obvious: Adhere to the scientific method.
You have the reference for the original source, but you don't want to share it? If so, it is at least your duty to explain why, else the procedures
remain untraceable (no references!) and/or unverified (no experimental and analytic data bound to the responsibility of an author!).
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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BromicAcid
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There was a time when I was dreaming of something similar although not limiting the scope specifically to complex compounds. More or less a database
with a record set updateable by anyone where one would enter the reagents used in the experiment, a short description of the experiment, and the
outcome. The purpose of which would be to categorize all experiments, especially the ones that did not work or didn't give the expected results.
This is especially important because if an experiment doesn't give expected results many people will just dismiss it, otherwise this forum would be
completely flooded with those types of questions instead of the trickle we see.
So, for example, you might search something common like potassium permanganate and see dozens or hundreds of experiments people had done with results
like 'No Reaction' or 'It spattered purple everywhere' or 'Strange precipitate that deflagerates on heating'. It would function as a initial check on
a given experiment to act as a heads up.
At the time I put a lot of effort into getting this started but alas after talking to several people I found that it likely wouldn't achieve the
critical mass necessary to be a useful tool.
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fledarmus
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@ BromicAcid - that database of reactions that didn't work is something I've been wishing for for years in organic chemistry. It's fairly easy to do
structure searches and find all the compounds people have made and the reactions that have worked, but almost impossible to find out what sorts of
reactions and conditions people have tried that didn't work. Only a very few get published, and they are not usually searchable.
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blogfast25
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I put Endimion’s procedure for potassium trioxalo ferrate (III) trihydrate to the test today with good results.
I scaled up by a factor 10, synthesised the potassium oxalate from KOH and oxalic acid and used 35 % H2O2 (quantity adjusted) instead of 20 %.
Temperature control during oxidation wasn’t as stringent as recommended because the oxidation reaction is highly exothermic. To really control
temperature better, icing would be required, IMHO. But it made not a jot of difference: after adding the last drops of oxalic acid solution, the
solution/suspension cleared up wonderfully from a ferric oxide style deep red-brown to a perfectly clear emerald green solution (100 ml) of potassium
trisoxaloferrate (III). After filtering (not even really needed!) and cooling, alcohol (50 ml) was slowly added and the first green crystals appeared
almost at once. The solution is now being kept overnight in my lab fridge, a nice crop of crystals has already formed. After further washing the
product will be dried and yield determined and used in this thread.
Interesting to see a green ferric complex…
Update:
The crop of crystals was first washed several timed with chilled 1:1 water/alcohol, then with several aliquots of acetone. After leaking out on
filter, it was gently dried in the dark on a low setting hot plate to constant weight. About 18.3 g of K3Fe(C2O4)3.3H2O was obtained, about 73 %
actual yield based on 20 g of Mohr’s salt:
[Edited on 22-10-2011 by blogfast25]
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