Sr, Mg, and Transition Metal Soaps!

Hello,

I've been experimenting with traditional soap-making (NaOH + fat) for a while, and I thought making uncommon soaps from metals such as Pb or Co would be interesting, and I had such good results that I'd like to share in case anyone's interested!

I bought half a pound of stearic acid (CH3(CH2)16COOH) off of eBay to use in making the soaps. However, I also tried the method using traditional soap (see notes below) and copper(II) sulfate.

General Procedure

The procedure is fairly simple. Dissolve the stearic acid in hot, 95% ethanol, followed by the addition of a stoichiometric amount of KOH dissolved in as little H2O as possible, and then adding the water-soluble salt of the metal you wish to make the soap of. The soap precipitates out (1).

Variation

The procedure I used was a variation on the method above. I substituted 50% isopropanol solution (bought from a convenience store) for 95% ethanol because I did this indoors and did not want the horrible fumes going everywhere. I also used NaOH (sold as 100% lye) instead of KOH.

I followed the procedure using salts of Sr(2+), Mg(2+), Pb(2+), Co(2+), Cu(2+), Zn(2+), and Sn(2+), always obtaining the same results.

Synthesis

The quantities used were for making ~5g of the corresponding stearate salt, excess stearic acid was used to make sure no NaOH remained to prevent unwanted side reactions with the metal cations. At the end, pictures of the synthesis for copper(II) stearate are given, but all of the synthesis are pretty much the same.

Strontium Stearate
40mL of 50% isopropanol solution was added to a 50mL Erlenmeyer flask and heated to ~45 C (about 25 degrees short of stearic acid's melting point) and to it, 4.9g of stearic acid was added. After stirring for about a minute, 0.6g of NaOH dissolved in H2O was added, resulting in a clear, colorless solution with left over undissolved stearic acid floating around. This was stirred for another 30 seconds to dissolve it, and then 1.6g of Sr(NO3)2 was added, resulting in a white precipitate that filled up the flask. The precipitate was then washed three times with H2O, melted, and poured out onto a watch glass to freeze.

Magnesium Stearate
The same amount of isopropanol solution was heated to 45 C, and then 5.3g of stearic acid followed by 0.7g of NaOH in H2O, and finally 2.1g of MgSO4*7H2O, yielding a white precipitate. The precipitate was washed with H2O and put onto a watch glass (I did not melt this one).

Lead(II) Stearate
Lead(II) acetate was the salt used for Pb(2+), and was prepared by mixing an arbitrary amount of 3% H2O2, vinegar (5% acetic acid), and adding 3 lead fishing sinkers weighing ~15 grams each. The solution, being cloudy due to chloride impurity in the vinegar, was then filtered (twice) and used.

The isopropanol solution was heated to 45 C, followed by addition of 5.1g of stearic acid and 0.7g of NaOH, and finally lead(II) acetate solution was added until no more of the white precipitate was produced. This was washed with H2O, melted, and poured onto a watch glass.

Cobalt(II) Stearate
The isopropanol solution was heated to 45 C, then the addition of 5.0g of stearic acid followed by 0.7g of NaOH. Finally, 1.9g of CoCl2*6H2O was dissolved in H2O and added to the stearate solution, producing a nice purple precipitate which I felt compelled to show here:

On a side note, addition of NaOH to a regular solution of CoCl2 produces a blue precipitate.

Zinc Stearate
ZnSO4 solution was prepared by dissolving 1.0g of Zn metal powder in 0.8g of drain cleaner H2SO4 diluted with an equal volume of H2O, with excess Zn being used to limit the remaining H2SO4.

40mL of isopropanol solution was heated to 45 C, followed by the addition of 5.0g of stearic acid and then 0.8g of NaOH. The Zn(2+) solution was then added until no more of the white precipitate was produced. This was washed with H2O, melted, and poured onto a watch glass.

Tin(II) Stearate
1.5g of SnCl2 was previously acidified to minimize the hydrolysis of Sn(2+). The amount of NaOH was slightly higher to account for this.

40mL isopropanol solution was heated to 45 C, followed by the addition of 4.6g of stearic acid and 0.6g of NaOH, and finally the acidified SnCl2 solution, producing a white precipitate, which was washed with H2O, melted, and poured onto a watch glass.

Copper(II) Stearate
This one is last to add pictures of the process.

The reagents used were 4.8g of stearic acid, 2.1g of CuSO4*5H2O, 0.7g of NaOH, and 40mL of 50% isopropanol:


The isopropanol solution, following addition of stearic acid with additional stirring, is still quite cloudy:


With the addition of NaOH, the solution goes nearly totally clear and colorless:


Finally, the addition of the CuSO4 solution results in a nice blue precipitate:


After washing it with H2O and melting it, it is easily poured onto a watch glass to freeze:



Notes

Although I did this with stearic acid, I also tried the same procedure using soap prepared by mixing NaOH with canola oil, dissolving it in 95% ethanol, and adding CuSO4, resulting in a blue precipitate. So it should work for 'normal' soap.

I did not try and measure the yield, as the products did not dry quickly and I did not have much time, but from the amounts produced, it sure looked like alot.

Finally, the reference I give mentions that the products can be recrystallized from hot benzene. I was going to use toluene as it's more convenient, but, unfortunately, ran out of time.


Well, that's it. Hope someone finds this interesting . The thing I found interesting about these compounds was that all of them melt easily at low temperatures, something not found in common metal salts!

Reference:
1.“Properties of Molten Carboxylates,” Ekwuriff, M.E., Nwachukwu, M.U., Rinehart, F.P., and Sime, S.J., J.C.S., 1974, 1432

[Edited on 9-3-2008 by kryptic]

UnintentionalChaos,

I do have some reagent grade stearic acid, but the stuff I purchased was probably intended for the candlemaking like you describe. However, the main idea was to make soap, and a mixture of stearic acid and palmitic acid still works well for that purpose

The soaps I made are also not sticky, like not_important's, although when wet they are kind of a hassle to try and transfer between containers...

I was hoping to try other metals like iron and nickel as well, but didn't have the time. They are probably alot more colorful than the metals I tried it with!

how did you go about isolating the oleic soap from the reactants?

[Edited on 10-3-2008 by kryptic]

I thought the cobalt soap is funny looking. Like Papa smurf went out binge drinking all night long and that bright purplish mass is what came out the other end in the morning!

I wanna play too. I have candlemakers stearic acid that I bought to "harden" my cold process soap recipes but maybe I should make some metal stearates.

Pretty Colors

If you think the cobalt one was bad, the magnesium soap was really massive, much more of that one probably because I isolated it better

What variety of metal salts do you have access to? The metals that produce pretty colors (Fe, Ni, etc) might be more interesting than the ones I did, most of those were white!

Random aside: the cobalt soap I have in a plastic bag likes to melt easily, the Pb and Sn not so much

[Edited on 11-3-2008 by kryptic]

Well I just ordered 10 pounds of nickel sulfate because I bought some for myself before but it sells like crazy on ebay! So I needed more. Might actually use some for my experiments

Quote: Originally posted by phlogiston

How about dissolving some Sr or Ba stearate in candle wax together with a chlorine donor (finely powdered chlorate maybe) to produce a red/green flame? I am also curious about the conductivity of the molten salts. If they conduct at all, perhaps it may be possible to produce the metals via electrolysis.

What are you talking about? I prefer barium soap over any other kind, even lead! It is the superior soap by far.

Quote: Originally posted by zts16

What are you talking about? I prefer barium soap over any other kind, even lead! It is the superior soap by far.

Quote: Originally posted by DraconicAcid

I don't think anyone would be silly enough to try using these as soap for washing. The calcium salt, at least, is well-known as "soap scum", and, while non-toxic, is utterly useless for washing (quite the contrary, it's difficult to get off).

Have you guys ever had halide soaps...? I prefer the bromine one, but....
(This soap is known to the state of California to cause cancer... )

Quote: Originally posted by The Volatile Chemist

Have you guys ever had halide soaps...? I prefer the bromine one, but.... (This soap is known to the state of California to cause cancer... )

Quote: Originally posted by The Volatile Chemist

Have you guys ever had halide soaps...? I prefer the bromine one, but....

Quote: Originally posted by blogfast25

Quote: Originally posted by The Volatile Chemist   Have you guys ever had halide soaps...? I prefer the bromine one, but.... What are you talking about?

Hahaha! I was joking!!! I was continuing the joke about using poisonous soaps.
you guys totally took that seriously!!!!!

[Edited on 3-29-2014 by The Volatile Chemist]

Quote: Originally posted by The Volatile Chemist

Hahaha! I was joking!!! I was continuing the joke about using poisonous soaps. you guys totally took that seriously!!!!!