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darkflame89
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[*] posted on 18-8-2004 at 02:11
sodium percarbonate


Does anyone have a clue on how to synthesise sodium or potassium percarbonate. The only info i have about it is that it evolves O2 in water, decomposing to the carbonate.



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JohnWW
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[*] posted on 18-8-2004 at 02:37


I remember reading somewhere that percarbonates have a blue color, and are made by electrolysis of alkali metal carbonates (which in solution are alkaline due to hydrolysis) at low temperatures at a voltage sufficient to discharge OH- ions.

John W.
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guy
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[*] posted on 19-8-2004 at 22:11


Na2CO3.H2O2

Maybe it could be made by adding anhydrous soda ash to pure hydrogen peroxide.




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darkflame89
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[*] posted on 20-8-2004 at 02:23


really is that easy?



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JohnWW
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[*] posted on 20-8-2004 at 03:02


I rather doubt it, except in small amounts, because H2O2 is rather too easily decomposed. However, if H2O2 could be cleaved at the O-O bond to form OH radicals, this would have the same effect as the OH radicals formed on discharge of OH- anions in the method for preparation involving electrolysis of Na2CO3 solution.

At least one of the Os in the CO3-- anion has to be replaced with C-O-O, to give CO4-- (similar to Caro's acid and peroxysulfate), or a bridged structure like [O2C-O-O-CO2]-- (similar to peroxydisulfate). If partial discharge of CO3-- anions is significant in the electrolysis of Na2CO3 solution, forming singly charged CO3- radicals, two of them could combine to form the latter (bridged) species.

John W.
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halogen
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[*] posted on 20-8-2004 at 08:57


It comes in the impure form as oxiclean.
(sodium percarbonate)
But even then, it has a lot of carbonate too...




F. de Lalande and M. Prud'homme showed that a mixture of boric oxide and sodium chloride is decomposed in a stream of dry air or oxygen at a red heat with the evolution of chlorine.
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neutrino
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[*] posted on 20-8-2004 at 09:45


Quote:

At least one of the Os in the CO3-- anion has to be replaced with C-O-O, to give CO4-- (similar to Caro's acid and peroxysulfate), or a bridged structure like [O2C-O-O-CO2]-- (similar to peroxydisulfate). If partial discharge of CO3-- anions is significant in the electrolysis of Na2CO3 solution, forming singly charged CO3- radicals, two of them could combine to form the latter (bridged) species.

John W.


Huh??? Sodium percarbonate is just Na2CO3.1.5H2O2, with only standard ions. Acros gives the structure here.

[Edited on 20-8-2004 by neutrino]
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JohnWW
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[*] posted on 20-8-2004 at 12:57


That (with that formula) would not be a true percarbonate at all, but just a double salt, a mixture of sodium and hydrogen carbonate and peroxide, obtained by crystallization from a mixture of carbonate and peroxide, which someone has chosen to call "percarbonate". I am sure that true percarbonates exist, however.

John W.
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neutrino
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[*] posted on 20-8-2004 at 13:48


Well, that's what's sold commercially as percarbonate.
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[*] posted on 20-8-2004 at 19:38
Oxyclean


If I recall correctly, the otc commercial cleaning agent sold as "Oxy-Clean" is a mixture of sodium carbonate and sodium percarbonate.

I know it doesn't help with the synthesis, but a good addition to the search engine nonetheless....

-T
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guy
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[*] posted on 20-8-2004 at 19:44


Percarbonates are not CO4 salts.

My Penguin Dictionary of Chemistry states that percarbonates are:

Carbonates with varying amounts of H2O2 of crystillation are stale as solids.

[Edited on 21-8-2004 by guy]

[Edited on 21-8-2004 by guy]




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[*] posted on 20-8-2004 at 20:53


There has been confusion over the nomenclature for at least a hundred years. There are a few different salts that one could make with, say, K2CO3. For some reason industry calls the one with H2O2 of crystallization percarbonate. From Kirk-Othmer:

"Peroxocarbonates contain the C-O-O- group and should be distinguished from the carbonate peroxohydrates. Although no crystal structures have been determined, the nature of the peroxocarbonates has been deduced from vibrational spectra.

These compounds can be prepared by three general methods: reaction of carbon dioxide and a solution of the metal hydroxide in hydrogen peroxide, anodic oxidation of normal carbonates at low temperatures, and oxidation of aqueous solutions of carbonates with elemental fluorine. Only the peroxocarbonates of the alkali metals are known. Some are peroxomonocarbonates, containing the CO2-4 anion; others are peroxodicarbonates, containing the C2O2-6 anion. Mixed alkali metal hydrogen salts are also known. Those salts that have been reasonably well-characterized include Li2(CO4)·H2O, Na2(C2O6)·nH2O, K2(C2O6), Rb2(C2O6), Cs2(C2O6), NaHCO4·H2O, KHCO4, and RbHCO4.

Sodium Carbonate Peroxohydrate. Known commercially as sodium percarbonate, sodium carbonate peroxohydrate [15630-89-4] does not contain the C-O-O-C group and is not a peroxocarbonate. The stoichiometry is 2Na2CO3·3H2O2. The material is made commercially by three processes: batch crystallization, continuous crystallization, and fluid-bed reaction. The crystallization processes are similar to the processes for making sodium peroxoborate hexahydrate. Solutions of hydrogen peroxide and sodium carbonate are mixed in proportions close to the stoichiometry of the end product. Stabilizers are added and the product is separated by cooling and the use of salting-out agents such as sodium chloride. In the fluid-bed process, hydrogen peroxide solution and sodium carbonate solution are injected into a fluid bed of the product fed by warm air. The bed serves as a combined reactor, granulator, and drier. Stabilizers are usually introduced with the hydrogen peroxide...

Because the compound is alkaline (pH 10-11 in solution) and hydrogen peroxide is unstable in alkali, the hydrogen peroxide liberated from the peroxohydrate tends to decompose as it escapes. The peroxohydrate is storage-stable if dry, but unstable if wet. The ready availability of hydrogen peroxide from the peroxohydrate, often an advantage in synthetic applications, can lead to violent exothermic reactions if the peroxohydrate is mixed with an excess of an oxidizable substance.
When dissolved in water, the solution is identical with that obtained by dissolving sodium carbonate in aqueous hydrogen peroxide. There is some evidence for the presence of the traces of true peroxocarbonate anion, HCO-4, in these solutions. If the peroxohydrate is heated for about an hour at 100°C and then allowed to cool to room temperature, some decomposition occurs and the product effervesces when placed in water...

Sodium carbonate peroxohydrate has been used as an oxidizing agent in synthetic organic chemistry, at least on the laboratory scale. In nonaqueous systems it serves as a source of concentrated hydrogen peroxide and thus can be used to make peroxycarboxylic acids from carboxylic anhydrides, chlorides, or imidazolides. The peroxohydrate does not need high solubility to react. A suspension of sodium carbonate peroxohydrate in tetrahydrofuran, or dichloromethane presaturated with water, can be used. These heterogeneous reactions can be accelerated by ultrasonic radiation."
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darkflame89
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[*] posted on 21-8-2004 at 01:00


Perhaps I am misunderstood, when i wrote potassium percarbonate, i mean K2C2O6. This compound decomposes to potassium carbonate, oxygen in water, and is certainly not potssium carbonate solution with hydrogen peroxide in it.



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[*] posted on 21-8-2004 at 13:38


That would be the bridged dimeric anion [O2-C-O-O-CO2]-- I postulated before, as capable of being formed from the singly charged radical anions CO3- formed in the partial electrolytic discharge of CO3-- anions.

JohnW.
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[*] posted on 21-8-2004 at 15:01
Percarbonates


I buy my sodium percarbonate from www.chemistrystore.com in 2 lb jars. It is great for laundry and I use the powder as a scouring powder for heavy duty scrubbing. Mix this with strong alkali like sodium metalsilicate or trisodium phosphate and this stuff will lift many kinds of dirt and grime. It is excellent for bleaching wood!:cool:



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Mendeleev
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[*] posted on 19-12-2004 at 00:58


Is sodium percarbonate a stronger oxidant that sodium perborate?



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[*] posted on 19-12-2004 at 01:23


Mendeleev

IICR sodium perborate (Na2B2H4O8-is this right?) is a stronger oxidant than sodium percarbonate (Na2CO3).
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Mendeleev
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[*] posted on 19-12-2004 at 08:07


I believe this is because Na2CO3 is sodium carbonate not percarbonate.

[Edited on 19-12-2004 by Mendeleev]
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[*] posted on 19-12-2004 at 13:10
Sorry


Mendeleev

Sorry, I was kind of buzzed last night, didn’t even bother to re-read my post.
Na2CO3-H2O2, Sodium Percarbonate has an active available oxygen content which is equivalent to abotu 27.5% H2O2, (I think).

[Edited on 20-12-2004 by Joeychemist]
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