Sciencemadness Discussion Board - Al acetate from Al metal and acetic acid

Al acetate from Al metal and acetic acid

wg48 - 17-2-2018 at 16:42

I attempted to make Al diacetate hydroxide (or any soluble Al acetate) by dissolving Al metal in a 50/50 solution of acetic acid and water. The small scale seemed to work ok with a drop of HCl and a small crystal of copper sulphate added to the solution before adding the Al metal. I then heated it on a water bath to about 100C.

So I moved on to a larger scale 60g of Al (cut up Al sheet) added to 220g of acetic acid and 220g of H2O. However its impractically slow. I estimate less than 6g has dissolved in about 20 hours. All the Al is a grey color suggesting no passivation.

I guess I will have to convert the Al to the hydroxide first. I was surprised how unreactive the Al is in hot acetic acid/water.

I just noticed crystals are growing on a piece Al sticking out of the solution. Suggesting a saturated solution of an Al mono/di/tri/acetate. Perhaps I should try adding more water I only need a dilute solution. I should check my mass calulation too.

Interestingly the thermal decomposition of Al diacetate produces acetic anhydride.

Here is pic. Sorry about the crap quality.

[Edited on 18-2-2018 by wg48]

RawWork - 17-2-2018 at 17:37

I will do that reaction before spring comes, just subscribe to my yotutube channel so you don't miss it first

: https://www.youtube.com/channel/UCPmTPa2-8PM2lDdIt9SHw0g

clearly_not_atara - 17-2-2018 at 17:53

Can you confirm the anhydride production? IIRC this was in an old reference but attempts to recreate the procedure failed.

wg48 - 17-2-2018 at 18:33

Quote: Originally posted by clearly_not_atara

Can you confirm the anhydride production? IIRC this was in an old reference but attempts to recreate the procedure failed.

No I cannot confirm anhydride productions by experiment. I read it when researching the thermal decomposition of the acetate.

From wiki:

On heating, aluminium triacetate decomposes above 200 °C in a process similar to that of aluminium formate.[3] The process begins with loss of acetic anhydride (Ac2O) between 120 and 140 °C[1] to form the a mixture of the basic oxide acetates such as Al2O(CH3CO2)4 and Al3O(CH3CO2)7,[30] which are ultimately transformed to Al2O3 (alumina), first as an amorphous anhydrous solid and then through other solid phases (γ-, δ-, and θ- crystal forms) to ultimately become polymorphic α-Al2O3:[3]

[Edited on 18-2-2018 by wg48]

clearly_not_atara - 17-2-2018 at 19:15

Sometimes a salt loses the equivalent of acetic anhydride as a mixture of carbon dioxide and acetone. Note that the equation (MeCO)2O >> Me2CO + CO2 is balanced.

Two equivalents of acetic anhydride can react to give acetic acetoacetic anhydride and acetic acid by an enol acylation. Acetic acetoacetic anhydride then transfers an acetyl group to acetic acid to release acetoacetic acid, which decarboxylates to acetone. So Ac2O can catalytically decompose. In particular this happens when protons are present, because this catalyzes enolization. But aluminium diacetate (AcO)2AlOH always has a proton available, so the chance of Ac2O being obtained from this salt is poor. Because acetic acid has a proton the decomposition is "autocatalytic" and can be "ignited" by a small amount of catalyst.

Aluminium triacetate might release Ac2O on decomposition if it is rigorously dried beforehand. But it is very hygroscopic. Zinc acetate releases a 25% yield of acetic anhydride and decays to zinc oxyacetate. Silver acetate works if it is dry in a dry atmosphere. Copper (II) acetate decomposes (likely involving oxidation of acetate) but copper (I) acetate might work well.

Edit: https://en.wikipedia.org/wiki/Aluminium_triacetate

I bet you could make aluminium triacetate by heating aluminium in GAA containing an alternative drying agent like sodium pyrosulfate, metaphosphoric acid, etc.

[Edited on 18-2-2018 by clearly_not_atara]

Waffles SS - 17-2-2018 at 22:12

Aluminium triacetateAl(O2CMe)3,can be prepared by heating AlCl3 or al powder with a mixture of acetic acid and acetic anhydrid

Chemistry of aluminium, gallium, indium, and thallium

http://books.google.com/books?id=v-04Kn758yIC&pg=PA158&a...
By Anthony John Downs

I have experience on making Aluminium Acetates.Aluminium Triacetate is not stable in aqueous solution

[Edited on 18-2-2018 by Waffles SS]

wg48 - 18-2-2018 at 23:57

I have experience on making Aluminium Acetates.Aluminium Triacetate is not stable in aqueous solution

[Edited on 18-2-2018 by Waffles SS][/rquote]

I was hoping the diacetate would precipitate out as its only about 6% soluble in water and the least soluble of the three acetates. I could then recover it by filtering. I could then redesolve it to make a dilute water solution that would be stable for sufficient time (5 minutes) to apply it to ceramic insulation to bind that insulation as it dries and ultimately is heated 1200C. Its to fix a heating element in MgO powder

A small quantity of a white precipitate did form. I have not tested it yet. Do you expect that to be the hydroxide ? Does the solubility of the dicacetate increase significantly with temperature and decrease in acetic acid solutions?

Waffles SS - 19-2-2018 at 00:36

Infact Aluminium Triacetate lead to Aluminium hydroxide acetate hydrate in aqueous solution.it will precipitate out after a while.

AJKOER - 19-2-2018 at 10:15

Quote: Originally posted by wg48

A similar (but perhaps improved) electrochemical cell approach as detailed above (research, for example, 'bleach battery' on SM including my observations and comments at http://www.sciencemadness.org/talk/viewthread.php?tid=33247#... ) would be Al/Cu in acetic acid and a good dose of NaCl (raising the 'activity coefficient' of the dilute acidic acid in addition to functioning as an electrolyte and possibly removing any passive layering on the aluminum itself, see “REACTION OF ALUMINIUM WITH DILUTE NITRIC ACID CONTAINING DISSOLVED SODIUM CHLORIDE: ON THE NATURE OF GASEOUS PRODUCT”, by Vladimir Petrusevski, et al, at Chemistry Education in New Zealand, May 2011, p. 7., at https://www.researchgate.net/publication/215904100_REACTION_...).

Jump start the reaction in a microwave.

[Edited on 20-2-2018 by AJKOER]

wg48 - 23-2-2018 at 17:03

Quote: Originally posted by wg48

I attempted to make Al diacetate hydroxide (or any soluble Al acetate) by dissolving Al metal in a 50/50 solution of acetic acid and water. The small scale seemed to work ok with a drop of HCl and a small crystal of copper sulphate added to the solution before adding the Al metal. I then heated it on a water bath to about 100C.

So I moved on to a larger scale 60g of Al (cut up Al sheet) added to 220g of acetic acid and 220g of H2O. However its impractically slow. I estimate less than 6g has dissolved in about 20 hours. All the Al is a grey color suggesting no passivation.

The reaction mixture has been left for 7 days. It has continued to bubble at very slow rate.

I had some 11% H2O2 that I did not want to return to the stock bottle so added about 30ml of it to the reaction mixture. It immediately produced some white cloudiness with no fizzing. After about 5 minutes the mixture was vigorously fizzing and hot. The cloudiness is now a dark grey colour and much denser, its impossible to see the Al unless its within a few mm of the glass.

So what might the grey precipitate (I assume) be ?
It’s reminiscent of a fine nickel powder suspension. I strongly doubt its aluminium powder or carbon.

DraconicAcid - 23-2-2018 at 20:15

If you're using aluminum foil, it usually contains silicon as an impurity that gives a grey powder when the aluminum is dissolved.

wg48 - 23-2-2018 at 23:41

Quote: Originally posted by DraconicAcid

If you're using aluminum foil, it usually contains silicon as an impurity that gives a grey powder when the aluminum is dissolved.

The initial reaction of the Al with ~100C 50/50 acetic acid/water did not produce a grey precipitate. The Al surface did turn grey which I assumed was due to its texture but it could have been due to silicon powder adhering to the surface, which slowed the reaction with time.

The Al is from a heat sink. Your suggestion reminded me of the grey precipitate that is produced when I have dissolved Al in NaOH./water. Perhaps the addition of the H2O2 and water produced a sufficiently vigorous reaction that the silicon was dislodged from the surface to produce the grey precipitate.

wg48 - 24-2-2018 at 06:53

Quote: Originally posted by wg48

Quote: Originally posted by DraconicAcid

If you're using aluminum foil, it usually contains silicon as an impurity that gives a grey powder when the aluminum is dissolved.

So on the assumption the Al may be more reactive now, I have reheated the reaction mixture up to ~100C.
Surprisingly the dark grey precipitate has turned light grey and the Al appears to be dissolving again with significant bubbling. Perhaps the fizzing was due mostly to decomposition of the H2O2 in body of the liquid. I think the larger bubbles are due to the small bubbles produced at the surface of Al coalescing as they ascend through the tangle of Al. I will let it remain at ~100C while the Al continues to dissolve.

The surface of the Al now appears darker possibly due to the contrast wrt the now much light grey precipitate.

Does finely divided silicon react with water or acetic acid at ~100C ?

AJKOER - 1-3-2018 at 08:09

It is an interesting fact that uncovering the precise Al alloy employed in a particular aluminum product is not easy. For example, most aluminum foil marketing sites avoid precise metal content or reference Al alloy composition. Here is one site that is an apparent exception http://www.totalmateria.com/page.aspx?ID=CheckArticle&si... .

But why is that so? Perhaps because the other metal(s) added to increase strength or other qualities may not be well received by the consumer is one guess. Per this source https://books.google.com/books?id=dUgzGsEMhoUC&pg=PA353&... , the possible other metal(s) added to alloys used for Aluminum foil, which could meet this criteria, include the likes of Cr, Cu and Mn, where I am ignoring some Al alloys with Sn, Ni, Bi and Pb not used in foil and not likely in food handling.

Try changing your aluminum source (perhaps an aluminum soda can) and see if there are any visible differences. Note, Si (avoid) may be found in aluminum sheet, plate and wire (an application with apparently one of the largest variety of all other possible alloy metals commonly employed with aluminum as does aluminum rods).

[Edited on 1-3-2018 by AJKOER]

wg48 - 4-4-2018 at 10:09

The Al has been left in the acetic acid solution for over 7 weeks now. It continued to react slowly releasing hydrogen as the percipitate increased. About 5 days ago I noticed the once clear solution, above the precipitate and Al pieces, was now cloudy. The following day the solution was opaque but still mobile. It is now turned very thick presumable gelatinous Al hydroxide or basic acetate. The bubbling has almost ceased probably because the solution is now too thick to circulate. It still smells of acetic acid but less strongly than originally.

I speculate that the aluminium would continue to react even if in excess wrt the acetic acid, the acetic acid acting as a catalyst. I adjusted the gama on the pic below to attempt show the difference between the bottom granular precipitate and the thick solution.

alAcOH3.jpg - 5kB

AJKOER - 5-4-2018 at 07:11

wg48: "I speculate that the aluminium would continue to react even if in excess wrt the acetic acid, the acetic acid acting as a catalyst. I adjusted the gama on the pic below to attempt show the difference between the bottom granular precipitate and the thick solution."

Even with the acidified bleach battery (from Al/Cu/HOCl, where the hypochlorous acid employed was from CaCl2 + NaOCl(aq) + CO2 + H2O after removing CaCO3), it just forms Al(OH)3 and Cl2. No AlCl3 present (as if any formed, likely breaks down with water into Al(OH)3 and HCl), but a basic aluminum chloride is possible.

Bottom line, not completely sure if there is any basic aluminum salt present other than just Al(OH)3. To test, extract some precipitate, wash very well and heat to decomposition. If a black sticky mess, acetate was present, else no.

[Edited on 5-4-2018 by AJKOER]