Sciencemadness Discussion Board

Calcium acetate, other carboxylic salts

bbartlog - 31-8-2009 at 10:36

Made a little over 100g of calcium acetate (from vinegar and eggshells), with a view towards either making some acetone via dry distillation, or else trying it as a catalyst for biodiesel production (along with barium acetate). Failing that I can make a gel with ethanol to show my kids...
Anyway, after trying some distillation (mason jar in an oil bath) at around 180 deg C, I see that vapor is being emitted, but very slowly. After a couple of hours I have somewhere between one and two grams of distillate, some of which is probably still water of hydration (I did bake off water of hydration earlier, but likely some remained).
Does anyone know what temperature is required to make the reaction proceed at a reasonable rate (like 90% conversion inside an hour)?

Second and more general: the decomposition of calcium acetate is sort of interesting from an organic chemistry point of view - it's asymmetrical, one of the carbon-carbon bonds in one of the acetate anions must get broken in order for the reaction to proceed:

Ca(CH3COO)2 -> C3H6O + CaCO3

Maybe this explains the slow rate of decomposition at relatively low temperature; it may be thermodynamically favorable, but breaking the C-C bond implies a pretty high barrier to cross.
Anyway, does anyone know whether other carboxylic salts of calcium decompose in an analogous way? If I heat calcium formate, will it decompose to formaldehyde and calcium carbonate

Ca(HCOO)2 -> CH2O + CaCO3

...or is there some other reaction that's favored? And what about calcium propionate or butyrate? Will their decompositon result in some ketone plus CaCO3, or does something else happen? This link, at least, suggests that calcium propionate gives carbon monoxide (along with the CaCO3), so I expect some of these products would be disappointing. On the other hand, I see that I'm not the only one who was curious about this: too bad I don't have full access here. Anyone have more information?

vaprizz - 31-8-2009 at 10:51

I think you will need at about 300°C oder more to get some Acetone I think. So use a stronger heating source!
I tried it once with an open gas flame and it worked very nice. It took about 2-3hours. Yield was around 30ml destillate from about 150g dry CaOAc
But the RB flask was a little bended after destillation.





Here some more information:
Quote:

Kinetics and mechanism of thermal decomposition of lithium, sodium, and barium acetates. Yakerson, V. I.; Rubinshtein, A. M. Kinetika i Kataliz, 2 (1961), 172-178.

CA abstract: Prepn. of ketones by thermal decompn. of Li, Na, and Ba acetates and prepn. of CH4 by thermal decompn. of NaOAc are studied.
Prepn. of ketone from NaOAc (at 419-74) and LiOAc (at 352-415°C) occurs in the melt and proceeds by 2nd-order kinetics. Ba(OAc)2 decomps. in the solid phase in accordance with the topokinetic Erofeev equation (CA 41, 4027c). The relation between the rate consts. and temps. is described by the Arrhenius equation. The energy of activation (E) and preexponential factors were calcd. E of prepn. of ketones from the acetates agree with E of vaporphase prepn. of ketone from AcOH on carbonates of the corresponding metals. This fact holds good also in the prepn. of CH4 from NaOAc and from AcOH on Na2CO3. The exptl. results and literature data verify the concept of the formation of a cyclic 4-membered activated complex and of the mol. mechanism of ketone prepn. A scheme is suggested for the prepn. of CH4 from NaOAc with participation of H2O included in the activated complex. A compensation effect exists for both types of decompn. of the studied acetates.
...
General Procedure: The dry distillation was carried out in a 50 mL round-bottomed flask fitted with a 10-cm Vigreux column connected to a microdistillation apparatus and the gas outlet was connected to a gas burette. The flask was heated with a hemispherical heating mantle and the reaction time was started when 350 °C reaction temperature had been reached (after ca. 25 min). Adipic acid (10.0 g, 68.4 mmol) was placed in the flask together with a magnetic stirring bar and the corresponding amount of base. The heating was started and the progress of the reaction was followed by measuring the gas evolution. When no gas was produced anymore, the reaction was stopped, the two phases separated and the organic layer analysed by GC analysis, GC-MS and NMR spectroscopy. The purity of the cyclopentanone was in all cases higher than 99%. Traces of unchanged adipic acid could be detected by 1H NMR spectroscopy. In the case of the re-use of the residue, adipic acid (10.0 g, 68.4 mmol) was placed in the flask together with NaOH (496 mg, 12.4 mmol) and distilled until gas production ceased. A new 10.0 g portion of adipic acid was placed in the flask and the distillation continued. Over seven cycles 36.4 g (90%) of cyclopentanone was obtained as a colourless liquid from 70.0 g of adipic acid. from Eur. J. Org. Chem. (2004) 2036-2039



[Edited on 31-8-2009 by vaprizz]

[Edited on 31-8-2009 by vaprizz]

[Edited on 31-8-2009 by vaprizz]

[Edited on 31-8-2009 by vaprizz]

[Edited on 31-8-2009 by vaprizz]

bbartlog - 31-8-2009 at 11:27

Very interesting. I had been thinking mainly in terms of two carboxylic anions being joined, as in the case of the acetate to acetone; but I see from your info that even in the case of a single anion you can get a self-join. Though adipic acid is dicarboxylic, which surely helps the conversion to a cyclic form. I'm guessing that an anion with one carboxyl group isn't going to behave that way, e.g. I don't think I'm going to get cyclopentane by decomposing sodium hexanoate... but who knows? In any case the general process is appealing in cases where the product is useful, since you can easily regenerate the carbonates.

S.C. Wack - 31-8-2009 at 11:55

430-490C, sweeping with preheated CO2 or nitrogen, is supposed to be ideal.

Nicodem - 1-9-2009 at 00:14

Bbartlog, please use the search engine. There are numerous threads discussing this type of reactions, with plenty of papers, reviews and references posted. Try searching by using ketonic decarboxylation, catalytic–pyrolytic ketonization, pyrolytic ketonization, pyrolysis / thermolysis of carboxylate salts, as keywords.

Find attached the paper you cited above: Thermochimica Acta, 389 (2002) 133-139.

Attachment: Thermal decomposition of the calcium salts of several carboxylic acids.pdf (176kB)
This file has been downloaded 3177 times

Vaprizz, what is the reference claiming the reaction proceeds via the radical mechanism that you depicted?

[Edited on 1/9/2009 by Nicodem]

solo - 1-9-2009 at 02:17

Vaprizz depiction of the mechanism was noted here...,

http://www.chemieunterricht.de/dc2/essig/hac-20.htm

kmno4 - 1-9-2009 at 03:29

Quote: Originally posted by solo  
Vaprizz depiction of the mechanism was noted here...,

http://www.chemieunterricht.de/dc2/essig/hac-20.htm

This mechanism looks unrealistically. This is not reference, just internet page.
I also tried thermal decomposition of calcium acetate, about 400 C, yield of acetone (light yellow) better than 90%. Some calcium reminder adhered to glass permanently :)

tetrahedron - 23-11-2012 at 05:42

Production Of Acetone By Means Other Than Fermentation
Quote:
Calcium acetate when heated at a temperature of about 380° C. decomposes, giving acetone and a residue of calcium carbonate, but at the same time the accompanying calcium salts present as impurities also react and acetaldehyde and various higher ketones are formed together with the condensation products. In addition other impurities (such as dumasin) and tar-like bodies are formed.

Read more: http://chestofbooks.com/science/chemistry/Distillation-Princ...


[Edited on 23-11-2012 by tetrahedron]

Random - 24-11-2012 at 02:55

I have also produced what I think is acetophenone by distillation of calcium acetate and iron (iii) benzoate. It was strong lab smell. Or maybe it was benzophenone, but I'm sure I made something. Just a few drops though, woked on mg scale in test tube.