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How To Make Copper Salicylate For Whistling Blue Rockets




Okay, here's how I made my fourth batch.

First I'll give an overview, then my procedure. Keep in mind that I only had high school chemistry (though it was a great course!) and that was 29 years ago (!) so please bear with me as I mutilate Good Scientific Procedure.

If my stoichiometry is correct, the mixing ratio of anhydrous copper chloride (CuCl) (#CH8091) to sodium salicylate (Na salicylate, in my notes) is 1:1.2. Here's the reaction:

CuCl + NaC7H5O3 = NaCl + CuC7H5O3

The C7H5O3 group is salicylic acid; we're transferring it from the sodium to the copper. Cu salicylate is far less soluble than NaCl, so it will precipitate out. As will the NaCl, if the solution is hypertonic. Solubility vs. temperature and such I know nothing about.

I start with 200 grams of CuCl and 240 grams of Na salicylate. This is very convenient, as the mixing ratio of Cu salicylate to ammonium perchlorate (AP) is--again, if my stoichiometry is correct (I'm terrible at lower math!)--1:3.96 or simply 1:4. So 200 grams Cu salicylate + 800 grams AP = 1 kilo of composition. I've ball milled two batches of the composition for two hours. That's too long--it cakes on the bottom of the jar and turns green.

Why does it turn green, you ask?

Cu salicylate appears to have at least 2, maybe 3, stable isomers at room temperature. The one I like the best, because it's pretty, is sky-blue fine-needled crystals. The other is a tarry, taffy-like forest green form. The possible third one is an ochre-colored fine powder.

The reaction of CuCl and Na salicylate must be done cold, or you'll get a big wad of the green tar. First time I did it this way--did the reaction hot, and got a nice green tar ball. I put the tar ball in the freezer then a coffee grinder. When I washed it with cold water, it turned to the sky-blue phase. If it gets warm again, as during ball milling, it turns green again. This shouldn't affect performance, but then all three batches I've made to date have turned green from getting warm at some point during processing, so I really don't know yet.

I tried drying some of the Cu salicylate in the oven at 225 deg. F, and it turned ochre, but still seemed to burn just fine. That may be a third isomer.

So: We want to keep our Cu salicylate cold or at least room temperature at all times, if we can.

The tarry phase is also evil for another reason: We need to wash out the NaCl (common table salt) that is the other product of our reaction. Sodium has a strong yellow emission line that will turn our blue flame white, if we don't eliminate it. We want a fine powder, not a tar ball, for this washing process. (Though, for all I know, the tarry phase may effectively exclude the sodium. I'm just too ignorant to know anything about that.)

Other comments: This process *should* be pretty non-toxic. The precursors aren't too evil, and the (main) products are common table salt and a form of blue aspirin. Desultory research on the Internet reveals that both Cu salicylate and Na salicylate have been used as analgesics, so I figure they can't be that toxic. Don't know about any other reaction products, though. Oh, and hot CuCl solution ate the plating right off the metal spoon I used to stir it the first time. And the liquid resulting from the reaction attacks stainless steel rather fiercely, so I recommend using all plastic implements in this process.

Our goal is to do this reaction cold, then wash the result to remove the NaCl, while maintaining our pretty blue crystals. With this in mind, this is how I proceeded on my fourth try:
  • Dissolve 200 grams CuCl in ~1 cup boiling water.

  • Dissolve 240 grams Na salicylate in ~2 cups boiling water.

  • Cool both to ~50 deg. F in an ice water bath (quickly, to avoid precipitation).

  • Pour the CuCl solution slowly into the Na salicylate solution, stirring constantly. See the pretty green tarry phase form instantly!

  • Stir constantly with a large plastic spoon for ~3 minutes.

  • For the first few minutes, the solution will stay a very dark forest green. Then a phase transition takes place, possibly even before you finish stirring in the CuCl solution. The blue crystals form rather rapidly. As this happens, the mixture goes from a liquid solution to fairly dense sky-blue slurry. (Really cool to watch--have the family gather round!) If the slurry becomes too dense to stir, just add more water, which also helps to wash out the NaCl

    [Then it was late, so I put it in the fridge overnight.]

  • Pour a bunch of the slurry into a coffee filter cone with standard coffee filter paper. Let it drip for an hour or so.

  • Remove the filter paper and semi-solid slurry and place it on a sequence of folded-up paper towels, replacing each paper towel when it is soaked.

  • When the paper towels stop absorbing water, dump the filtrate back into your reaction vessel and wash with ~1 liter or quart of cold water. Wash at least twice.

  • If you want to maximize your yield, you could skip the washing. If you want to intensify your blue, you might want to do several washings to get rid of that sodium.

  • Repeat the filtering process and allow the Cu salicylate to air-dry for as long as it takes.

  • Then you can mill up some comp!
The paper towels are my conjectured cheap hillbilly chromatography; an effort to draw the NaCl out of the Cu salicylate in a process akin to how they make weapons-grade plutonium, only different. I may be completely full of it with this step, but what the heck; "seems like a good idea."

Have fun, and please trade notes and improvements to this hillbilly process of mine!

Materials Needed
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