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CrO3

Maja - 29-6-2006 at 13:42

Ok, Having a lot of pyridine and I don't have anything to do it I decide to prepare some PCC from it, but here is the problem... I don't have any CrO3. I know that is it highly toxic ,but if safety precautions is taken everything is going to be all right. I browsed google, some other forums, vogel 3 & 5 editions, Modern inorganic chemistry, other books and didn't find anything useful. From one thread(I think it's in COCl2 preparation) in this forum I came up with this equation :

H2SO4 + K2CrO4 ---> K2SO4 + H2O + CrO3

Will this work ? And what is the details for this reaction ? Thank you very much for your help.

evil_lurker - 29-6-2006 at 14:30

You can purchase it here:

http://store.hvchemical.com/browse.cfm/4,460.htm

Magpie - 29-6-2006 at 14:44

"Chromium oxide" and potassium dichromate are also available from some pottery suppliers. These are very reasonably priced (pottery grade, of course) and there won't be any hazmat fees.

ethan_c - 29-6-2006 at 16:53

Quote:

Originally posted by Magpie
"Chromium oxide" and potassium dichromate are also available from some pottery suppliers. These are very reasonably priced (pottery grade, of course) and there won't be any hazmat fees.

This is when different oxidation states can be deceitful. The compound available in pottery stores is Cr2O3, not the extremely corrosive and carcinogenic CrO3, better known as chromic acid. Trust me on that.
Wherever you get it, there WILL be hazmat fees. Trying to make it yourself isn't wise for two reasons; first, obviously, it's carcinogenic and likes to react very exothermically and suddenly with almost any organic compound. Second, if you indeed find an appropriate reaction to produce it with more obtainable chemicals (as I did), it is almost impossible to dry- it is probably just about the single most hygroscopic chemical I've had experience with.
The two main uses for CrO3 are for chromium plating baths (any rim- or bumper-plating operations nearby?) and as an antiquated (there are much safer replacements now) yet still frighteningly effective glassware cleaning agent in combination with sulfuric acid. I have personally worked in two labs that still had it around from its cleaning heyday, so you could certainly find some old surplus if you looked hard enough. Else, as I said, there ARE going to be hazmat fees.

neutrino - 29-6-2006 at 18:34

The following thread from RS might prove to be useful:

A review of chromium compound synthesis

Quote:

Chromium trioxide: Add 1 part of a saturated solution of potassium dichromate to 1.5 parts of concentrated sulfuric acid (about 95%). Cool the solution in an ice bath to precipitate crystals of chromium trioxide. Decant off the acid solution and place the crystals on filter paper to absorb the remaining acid and moisture. The drying should be done in a desiccator to protect the crystals from moisture. Chromium trioxide can also be obtained by evaporating a solution of chromic acid to dryness. For high purity chromium trioxide see the procedure for chromium fluoride below.

...

Chromium fluoride: May be prepared by distilling a mixture of lead chromate and fluorspar (calcium fluoride) in concentrated sulfuric acid. The distillation receiver must be cooled to -100 C to condense the chromium fluoride and the entire apparatus must be protected from moisture. Glass will decompose chromium fluoride...

woelen - 29-6-2006 at 23:56

Obtaining K2Cr2O7 (or Na2Cr2O7.2H2O) is MUCH easier than obtaining CrO3, and a mix of the finely crunched dichromate with H2SO4 for most purposes is equally suitable as pure CrO3. One source of K2Cr2O7 is this: www.artcraftchemicals.com. And for K2Cr2O7 there are NO hazmat fees (at least not from this company), I can tell you from experience.

Maja - 30-6-2006 at 01:30

I think I will try the route with pottasium dichromate, because I have a few hundred grams laying around. Ethan_c, "How" hard is to get it dry and can you share with us some practical suggestions "how" to get it dry if you are saying that is "VERY HARD TO GET DRY"

. And I think I won't try to dry it ,because PCC reaction doesn't require anhydrous conditions, so slight excess of it won't hurt. Will post pictures

And yes in pottery suppliers you can get JUST Cr2O3 ,but not CrO3
'
P.S. I have just searched site suggested by evil_lurker
http://store.hvchemical.com/browse.cfm/4,460.htm
1lb costs just 23$ and 10lb just 65$ maybe I will just order it from that e-shop..

S.C. Wack - 30-6-2006 at 02:41

That price seems rather high. And AFAIK the only hazmat chromate is ammonium dichromate. Other chromates are not on the UPS or CFR hazmat tables.

I'm sure that some of the books that I've scanned have some preparation, but it's really so simple that you don't have to measure anything. The solubility of CrO3 goes way down with increasing H2SO4 conc. and decreasing temperature. Bisulfate is more soluble. Its not rocket science. The unrecovered acid is given something to oxidize so as not to freak out the eco-sensitive who somehow missed this thread.

So it figures that if one can get the sodium salt, that would be preferred due to the higher solubility at reasonable temperatures, as adding H2SO4 to hot solutions can be less fun. The adhering H2SO4 is removed with HNO3 in the books and journals, and by other methods in the patents.

I think that the dangers of Cr+6 have been a little popularly hyped in the past 10 years. I'd worry more about dichromate dust when transferring it than CrO3; I've been flamed for mentioning this hazard before, though. Cr+6 is more of a nasal hazard than anything else, as long as you don't handle it particularly recklessly.

(yes I'm aware of the use of Roman numerals)

ethan_c - 1-7-2006 at 00:19

Quote:

Originally posted by Maja
I think I will try the route with pottasium dichromate, because I have a few hundred grams laying around. Ethan_c, "How" hard is to get it dry and can you share with us some practical suggestions "how" to get it dry if you are saying that is "VERY HARD TO GET DRY"

. And I think I won't try to dry it ,because PCC reaction doesn't require anhydrous conditions, so slight excess of it won't hurt. Will post pictures

I, too, have a couple hundred grams of some alkali dichromates just sort of sitting around, and I, too, made some chromium trioxide with sulfuric.
Basically, I have no suggestions for you because I sort of failed. I let it sit under a heat lamp, and the driest it got was a viscous liquid, like old oil-based paint. I put it in a very efficient desiccator at school and that helped just slightly, dehydrating it into sort of more of a paste.
If your reaction doesn't require anhydrous conditions- go for the dichromate oxidation. Dry it as much as is feasible for you (I don't have ether or anything to spare, and I didn't want to use CH3Cl) and that should be fine.
I actually just got my paws on some fairly dry stuff (its slightly wet but at least its a POWDER) just today…anyways, those prices are GOOD as far as I've seen- however, the hazmat fee would certainly provide an incentive to buy whatever you might possibly need from that company in the forseeable future…

kyro8008 - 1-7-2006 at 12:03

I cannot vouch for this as it is currently on my todo list, but the other preps from this book are very good:

PREPARATION 62
CHROMIC ANHYDRIDE, CrO3

The addition of sulphuric acid to a solution of either a chromate or a dichromate liberates chromic acid which is very soluble and can exist in solution in the different forms, H2Cr04, H2Cr207 and CrO3, in equilibrium with each other. With the addition of a large excess of concentrated H2SO4, water is withdrawn from the hydrated forms and the anhydride separates in the shape of red needles.

Materials:
sodium dichromate, Na2Cr2O7-2H2O, 100 grams = 0.33 F.W.
36 N H2SO4, 400 cc

Apparatus:
8-inch porcelain dish.
glass plate to cover the 8-inch dish,
suction filter with glass marble,
glass-stoppered sample bottle,
tripod.
Bunsen burner.

Procedure:
Dissolve the 100 grams of sodium dichromate in 250 cc. of water and filter from any sediment. Add rather slowly with constant stirring about half of the concentrated sulphuric acid
until a slight permanent precipitate of CrO3 is formed. Let the mixture cool for half an hour or longer, then add slowly, while
stirring, the rest of the sulphuric acid. Let the mixture stand over night covered with a glass plate in order that the crystal
meal may become somewhat coarser. In such a crystal meal standing in its saturated solution, the smaller grains dissolve and their material deposits out on the larger crystals. But even now the crystal meal will be rather fine and it will at first run through the filter; if, however, while waiting, the mixture is heated with stirring to 100° and allowed to cool slowly, and this process is repeated once or twice, a more satisfactory product will be obtained.
To collect the crystals, use a suction filter, but place a small glass marble in the funnel instead of the usual plate and
paper. If the red crystals at first run past the sides of the marble, pour the liquid in the bottle repeatedly back on to the filter until finally the filtrate runs clear (see last sentence of Note 3 on page 5). After draining the crystals completely and pressing the surface with the round end of a test tube, stop the suction and pour 15 cc. of 16 N HN03 so as to wash down the sides of the funnel and cover the surface of the product. Stir up the product with this washing fluid for a depth of about half an inch. Suck dry and repeat the operation twice with 10 cc. of nitric acid each time.
Finally drain the red crystals as free of liquid as possible, transfer the crystals to a dry 8-inch evaporating dish and place this on a hot plate to let the nitric acid evaporate. When the product is dry and no longer gives off vapors of nitric acid place it in the glass-stoppered sample bottle.

S.C. Wack - 1-7-2006 at 13:38

I just want to point out the use of the phrase "large excess" in the above. This is a bit too vague (if the directions are not followed) as this can lead to the release of (ozonized, perhaps) oxygen with too large an excess.

chloric1 - 15-9-2024 at 03:43

As per the last procedure, I think the emphasis should be on the concentrated nitric acid wash. Concentrated nitric acid is a solvent for sulfuric acid. I’m absolutely positive that the crude chromium trioxide that initially deposits has concentrated sulfuric acid adhering to it. You will never get this dry! Nitric acid removes the sulfuric acid by solvent action and the chromic acid anhydride has low solubility in it.

Keras - 15-9-2024 at 07:42

I’m not even sure potassium dichromate is available in the EU, btw.
Which would make chromic acid out of reach of any garden variety European amateur chemist, unless you’re prepared to synthesise it yourself starting from chromium or chromium III salt.

[Edited on 15-9-2024 by Keras]

woelen - 16-9-2024 at 02:23

In NL it still is available as sodium dichromate for private individuals: https://www.labstuff.nl/contents/nl/d122.html
They also have potassium dichromate (kalium dichromaat).

Some pottery suppliers still sell sodium dichromate, technical grade.

I'm not sure whether labstuff ships to other EU countries.

Limac also sells dichromates:
https://www.limac.lv/catalog/params/category/100939/item/380...
https://www.limac.lv/catalog/params/category/100940/item/380...

You will have to fill in an end user declaration, but they do sell to private individuals. In the past, I purchased Na2Cr2O7 (anhydrous) from them.

unionised - 16-9-2024 at 02:44

I'm pretty sure PCC is unstable.
How will you keep it, and what will you use it for?

Keras - 16-9-2024 at 08:47

Quote: Originally posted by woelen

Limac also sells dichromates:
https://www.limac.lv/catalog/params/category/100939/item/380...
https://www.limac.lv/catalog/params/category/100940/item/380...
You will have to fill in an end user declaration, but they do sell to private individuals. In the past, I purchased Na2Cr2O7 (anhydrous) from them.

Oh Linards do sell those. Good to know. Thanks for the info.

chloric1 - 27-9-2024 at 21:12

I have a pottery pigment supplier next state over that ships quickly and sodium dichromate is a recent addition to their inventory. They lowered the price recently to $6 per pound!!! I got 3 pounds because I want to prepare other chromium compounds of different valences.

I will probably end up recycling my dichromates using bleach but trouble is the extra ions introduced. So really I would think it will be better to isolate a neutral chromate first before trying to get to the other dichromates. Or alternatively drop most of the hexavalent chrome as slight soluble strontium chromate. Was the precipitate thoroughly and suspended with stirring in a hot solution of desired bisulfate until strontium sulfate change over is complete

Random - 28-9-2024 at 05:18

Chromium can be obtained from Stainless Steel

...

There was this efficient dichromate Synthesis

Was it dichromate

...

It could be prepared also in aqueous solution acvording to my personal memory. Without having to fuse at high temperature.

...

But that is according to my personal memory.

Keras - 29-9-2024 at 11:19

So, I had that chromium III oxide (green powder) left over from my very beginning in home chemistry when I thought I could easily transform it into chromium VI. Of course that was a dud. The chromium oxide I have is a pottery pigment and is heavily annealed.

But, following what we do with manganese dioxide to get potassium manganate, I decided to test this reaction:

Cr₂O₃ + 4 KOH + KClO₃ → 2 K₂CrO₄ + KCl + 2 H₂O

For some reason (read: because I’m dimwitted) I screwed up the coefficients and ended up with half the stoichiometric quantity of potassium hydroxide. Oh well.

So I mixed up 0.2 mol [should’ve been 0.4] (11 g) of potassium hydroxide and 0.1 mol (~ 12 g) of potassium chlorate (from bleach) in a steel crucible. The crucible was put on the smallest burner of my gas hob with the flame at near minimum. When the mixture was fused, I added the green chromium oxide (0.1 mol = 15 g) in four portions with a spatula and mixed to obtain a sort of pasty green compound. I then increased the flame and a few seconds later the paste started to fizz and a very bright orange fusion zone swept through the mix (see picture).

I was left with what appeared to be a disappointing green crust (maybe that’s because I put only half of the needed quantity of hydroxide) but orange traces on the crucible made me think that the reaction had at least partially succeeded. I therefore broke up the crust, put the 'shards' in a beaker, added 150 mL of water and started the magnetic stirring. After a while, all the pieces had dissolved and when I turned stirring off I was left with a definitely bright orange solution, and a slurry of green unreacted chromium oxide at the bottom.

At this point my cheap Chinese vacuum pump decided to quit on me so I was left with gravity filtration only. I didn't want to clog any of my sintered funnels with inert chromium oxide I could probably never have gotten rid of, so I opted for a coarse ceramic funnel with a glass fibre filtering disc. Unfortunately the finest particles of chromium oxide passed through, so I was left with a nice Cr VI solution with like green dust at the bottom.

Since this was a proof of concept, I decided to carry on and boiled the solution until the volume of water had decreased to 50 mL. At which point I cut off the heat and let the solution cool, and an appreciable amount of what I think is potassium dichromate crystallised as the solution cooled.

It is definitely polluted by Cr III oxide dust, there is probably some KCl in it too. Really, I didn't even bother to look at the solubility data, this was done by the seat of my pants. Now I’ll need to recrystallise (→ redissolving, filtering on Celite and maybe precipitate as chromium oxide to separate from KCl) and probably redo the experiment using the correct amount of potassium hydroxide. Nevertheless, it definitely worked to some extent, so it’s possible to get potassium dichromate from pottery grade chromium III oxide.

[Edited on 29-9-2024 by Keras]

chloric1 - 14-11-2024 at 03:15

Quote: Originally posted by Random

Chromium can be obtained from Stainless Steel

...

There was this efficient dichromate Synthesis

Was it dichromate

...

It could be prepared also in aqueous solution acvording to my personal memory. Without having to fuse at high temperature.

...

But that is according to my personal memory.

. Obtaining chemicals from eating utensils. Feasible yet ridiculous in context. I’ve seen the YouTube videos. Although I have pounds of Cr(IV) compounds, I remember that I accidentally dropped a spoon in the garbage disposal. Got chewed up bad so I might make some potassium dichromate with it for shits and giggles

This is my last hurrah with home chemistry. The global elite is gradually tightening its tyrannical grip. Covid was a practice run. They want us to stay home and collect government benefits and take away property ownership. The whole world will be like North Korea.