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kryptic
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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]
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guy
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that is very interesting
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UnintentionalChaos
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I have some experience with copper soaps...I made some by mixing copper sulfate solution with saponified olive oil...Am I right that transition metal
soaps are the most evil unholy sticky things you will ever encounter? I might have to make some now to see how stearic soaps behave compared to my
homebrew (mostly oleic) soap. I think I have a bag of stearic acid actually...it's used in candlemaking as a hardener...unless you purchased it as a
reagent, you likely have a blend of stearic and palmitic acids.
I'd be interested to see iron (II) and (III) soaps as well as nickel, chromium, and maybe a rare-earth soap...neodymium stearate?
[Edited on 3-10-08 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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not_important
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I've done Nd, Pr, Dy, Er, and Eu 'stearates' for some glaze experiments. Except for the Nd and Er they were quite pale in colour, those other two
while pastel were more noticeably tinted. Dried by azeotropic distillation in toluene, and crystallised from that. Soft powders, pressure gave soft
waxy flakes.
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UnintentionalChaos
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I'm glad to here the texture is much more tame with a saturated fatty acid. The oleic soaps melt easily in hot water and are extremely sticky and soft
like putty at room temperature. If anyone is looking to try this, for the sake of your sanity make stearates.
Not_important: I imagine the Nd stearate was a pale lavender...what did the Er stearate look like?
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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kryptic
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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]
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UnintentionalChaos
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I never did get it completely dry, but I melted it directly in the beaker I made it in and it all formed a nice melted blob on the surface. I then
poured the entire beaker's contents into a bowl of ice water, let it cool for a moment and fished out the hardened blob of deep green-blue soap. I
re-melted in distilled water and agitated the mass a few times to try to leach as much of the water-soluble contaminants out of the mass as I could
If I wanted very pure I would have gone to azeotropic drying and recrystallization, but it was for a failed project involving coloring a candle's
flame which only needed a crude product.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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JohnWW
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A use of Cu salts ("soaps") of fatty acids, which are soluble in common industrial organic solvents like mineral turpentine and kerosine and gasoline,
is as a preservative of untreated timber, and similar materials like string or rope derived from sisal or New Zealand flax. The most common one is
copper naphthenate, made using the "naphtha" fraction from crude-oil distillation, which is converted into naphthenic acid. However, Cu salts of
long-chain fatty acids of similar weight, derived from saponified tallow or vegetable oils of similar molecular weight, are possible alternatives
which could be tried as a wood preservative. Copper naphthenate is usually sold as a concentrated liquid in hardware stores as "Metallex" or similar,
having an intense green color. After dilution by a factor of 3 or 4, with turpentine or kerosine, it is usually applied to timber by painting or
spraying, although it could easily be used to impregnate dried pine timber right through under pressure, in the same way as creosote or copper
chromate-arsenate. For a colorless wood preservative, Zn is substituted for Cu as the naphthenate.
Also, a cobalt soap, usually the Co naphthenate, magenta in color, is used in small quantities as a catalyst in the polymerization of liquid
unsaturated esters (usually methyl methacrylate), with benzoyl peroxide as an initiator, in the making of glass-fiber-reinforced plastic (GRP, or
fiberglass) articles such as small boat hulls, of which I have personally made some.
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not_important
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| Quote: | Originally posted by UnintentionalChaos
Not_important: I imagine the Nd stearate was a pale lavender...what did the Er stearate look like? |
Nd was that, Er stearate a bit like Mn(II) salts, somewhat pale pink with a purplish tint. Er chloride is more strongly coloured than the stearate.
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chloric1
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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.
Fellow molecular manipulator
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kryptic
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Pretty Colors
| Quote: | Originally posted by chloric1
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! |
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]
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chloric1
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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
Fellow molecular manipulator
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numos
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I made some Copper stearate, and all three items it was in now have copper stearate smudges on the sides. Not stains but physical residue on the
sides. A 100ml 24/40 boiling flask, a 250ml Eryl. flask, and a small poly-prop. funnel.
How would I clean these? Scrubbing worked quite well for the funnel but I can't get inside the flasks, water doesn't dissolve it, and before I waste
any solvents, does anyone have an easy was to remove them?
Not sure whether to start a new topic, it seemed related enough, and I got the methods from this page so it seemed appropriate if others run into this
problem.
[Edited on 3-28-2014 by numos]
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DraconicAcid
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That's very interesting. To clean your flasks, numos, it sounds like a hot organic solvent should remove it. Ammonia might also work- complex the
copper, so pull it away from the stearate, which should be soluble in the basic solution.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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phlogiston
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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.
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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MrHomeScientist
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That's a very interesting idea phlogiston! What is the purpose of the chlorine donor, though? Does that intensify the color? I'd
think the cation (Na, K, etc.) would interfere with the desired color from the Sr or Ba, though. Unless of course you used Sr or Ba chlorate.
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Metacelsus
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The chlorine donor would need to be soluble in molten wax for it to make it into the flame. Alternatively, you could put it in the wick.
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Praxichys
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That's easy. Chlorinated wax is sold as a chlorine donor for fireworks.
http://www.skylighter.com/chlorowax.htm
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blogfast25
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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. |
I doubt if it will work. The most volatile Sr/Ba compounds are, as so often, the chlorides, obviously not the stearates. A candle won't produce enough
heat to volatilise them, never mind excite the atoms to emission. A chorine donor may alleviate things a bit, though.
Molten soaps are likely to decompose, IMHO.
[Edited on 28-3-2014 by blogfast25]
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The Volatile Chemist
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Hahaha, this was a great idea! Slight note though.... I saw some mention of Barium. Do NOT use a barium soap. I'm sure the coloration could be
interesting, but barium salts are horridly poisonous, attacking kidneys and nervous system. They are also slight carcinogens. It's not like it's
strong stuff, you could definitely make it, but washing with it is out of the question, as with a few other of the soaps you made. I'm sure you knew,
but just in case thought I should make it known.
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Texium
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What are you talking about? I prefer barium soap over any other kind, even lead! It is the superior soap by far. 
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DraconicAcid
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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).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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The Volatile Chemist
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| 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... )
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Texium
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Astatine soap anyone?
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blogfast25
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What are you talking about?
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