Polverone
Now celebrating 21 years of madness
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Zinc chloride
Let's discuss something really mundane, like ZnCl2! Okay, I want some ZnCl2 for making halides from alcohols. Vogel says to use conc. HCl and
anhydrous ZnCl2.
So I react a bunch of post-1981 US pennies with HCl (first using H2O2/HCl to penetrate copper shells) and am left with a bunch of heavy clear liquid
after filtration. The liquid goes into an evaporating dish and lands on the hot plate. Several hours of heating later, the liquid has turned golden
and has a thin skin on top of it. It is a syrupy consistency.
Stirring the liquid with a bamboo skewer, the skewer turns brown and then black. A piece of paper, with a drop of the solution upon it, bubbles and
turns black at the location of the solution when set on the hot plate.
There's a sort of sweet charred scent to the paper afterward, like I'd dripped H2SO4 on it.
What's going on here? Is ZnCl2 a powerful enough dehydrating agent to abstract water from compounds? Something else happening?
And - the real question - how long is this stuff going to heat before I get my anhydrous ZnCl2? Tune in soon for the exciting conclusion.
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Polverone
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The answer to "when will it go anhydrous?!" appears to be "not in this lifetime." Well, it's not quite that bad, but the evaporating dish full of
stuff takes a very long time to lose water. Interestingly, the color has changed again. It's now a dark wine-colored syrup sitting over a layer of
crystals that are tinted rose (presumably by the surrounding liquid). Improvising from household materials instead of buying lab grade certainly does
hold some interesting surprises.
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rikkitikkitavi
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why do you need anhydrous ZnCl2?
The HCl used is about 65 % water, so any anhydrous salt is going to absorb the water anyway?
/rickard
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Polverone
Now celebrating 21 years of madness
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The followup
It was taking so long to dry completely that I eventually abandoned the project altogether. The text specified anhydrous ZnCl2, so that's what I was
trying for. It used a relatively large amount of ZnCl2 and HCl with a small amount of alcohol. Perhaps anhydrous CaCl2, which I have ready access to,
could be used instead.
I still wonder what caused the very interesting tinting of the mixture.
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PHILOU Zrealone
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ZnCl2 is a Lewis acid and is a catalyst of this halogenation of alcohols!
As many catalyst it is specific!
Thus CaCl2 will not help!
Maybe AlCl3 or FeCl3 could help with conc HCl!
For primary alcohols you need catalyst and 100°C!
For secundary alcohols HCl conc and hot will do it and catalyst helps if there!
Tertiary alcohols do it at ambiant temp without catalyst with conc HCl!
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Hjalmar_Poelzig
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ZnCl2 and basic salts
When hydrated ZnCl2 is heated, one is left chiefly with Zn(OH)Cl and HCl.
If you want anhydrous ZnCl2, dissolve raw zinc metal in HCl, add a bit of KClO3 and evaporate the HCl.
The product will still contain a small amount of basic salts, but is usable for most purposes.
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Polverone
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thanks for the tip!
Is there a particular source that you obtained this information from, or is it just one of those things that's stuck in your memory and you
can't recall its genesis?
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solo
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Reductive Dehalogenation of Arylhalides and Alkylhalides with Zinc in THF Saturated Aqueous Ammonium Chloride
Rahim Hekmatshoar,* Sodeh Sajadi
Journal of the Chinese Chemical Society
2008, 55, 616-618
Abstract
A low-cost and highly effective zinc/THF-saturated aqueous ammonium chloride has been developed for dehalogenation of arylhalides and alkylhalides in
aqueous systems.
Keywords: Reductive dehalogenation; Zinc; Aqueous ammonium chloride.
Attachment: Reductive Dehalogenation of Arylhalides and alkylhallides with zinc in THF saturated aqueous ammonium chloride.pdf (64kB)
This file has been downloaded 438 times
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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AJKOER
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Per Atomistry http://zinc.atomistry.com/zinc_chloride.html on ZnCl2, a warehouse of historical recipes, to quote:
"The pure anhydrous salt of Zinc Chloride, ZnCl2, has been prepared by heating 3NH4Cl.ZnCl2 in a current of dry hydrogen chloride. The anhydrous salt
has also been prepared by distilling anhydrous zinc sulphate with sodium or calcium chloride, by the action of heated zinc vapour and hydrogen on
barium chloride, by distilling zinc with mercuric chloride, and by the action of chlorine on zinc oxide. Hydrous zinc chloride partially decomposes on
heating, but the anhydrous salt may be obtained from it by treatment with concentrated hydrochloric acid and evaporation in an atmosphere of hydrogen
chloride. It may also be prepared by adding zinc to molten lead chloride, passing dry chlorine into fused zinc, or by fusing zinc bromide in an
atmosphere of chlorine"
Also:
"A bluish-white mass of zincoso-zincic chloride, Zn3Cl5, results from the solution of metallic zinc in molten zinc chloride. It is very hygroscopic,
rapidly hydrolysed by water, and is probably best formulated as ZnCl.2ZnCl2.
Deliquescent rhombic crystals of the acid salt, 2ZnCl2.HCl.2H2O, separate from a solution of zinc chloride into which hydrogen chloride has been
passed when the density of the liquid at 25° C. is 2. At 100° C. they lose HCl, and anhydrous ZnCl2 is in contact with a concentrated solution of
the salt and hydrochloric acid. If this mother-liquor is treated with hydrogen chloride more crystals separate, and finally, if the liquid is
saturated with hydrogen chloride and cooled to 0° C., long needles of ZnCl2.HCl.2H2O crystallise. These readily lose hydrogen chloride in dry air and
form 2ZnCl2.HCl.2H2O."
A listing of possible double chlorides one may inadvertently create:
"The following double chlorides of zinc have been described: LiCl.ZnCl2.3H2O and 2LiCl.ZnCl2.2H2O; 3LiCl.ZnCl2.10H2O may exist; 2NaCl.ZnCl2.3H2O;
KCl.ZnCl2.2H2O and 2KCl.ZnCl2; 2NH4Cl.ZnCl2; 3NH4Cl.ZnCl2; 2RbCl.ZnCl2; 2CsCl.ZnCl2 and 3CsCl.ZnCl2Cl2; CaCl2.ZnCl2. 5½H2O and 2CaCl2.ZnCl2.6H2O;
SrCl2.ZnCl9.4H2O and SrCl2.ZnCl2; BaCl2.ZnCl2.4H2O; MgCl2.ZnCl2.6H2O; ZnCl2. PtCl4.6H2O."
And finally:
"Compounds of Zinc Chloride with Ammonia
The diammoniate ZnCl2.2NH4 is formed in the active Leclanche cell. It can be prepared by passing ammonia gas into an alcoholic solution of zinc
chloride, or by passing ammonia into a hot concentrated aqueous solution of zinc chloride, and, after cooling to separate the less soluble
tetrammoniate, ZnCl2.4NH4.H2O, crystallising the mother-liquor. The rhombic crystals are stable in air, insoluble in water or alcohol, and soluble in
acids, ammonia, caustic alkalies, and ammonium chloride. Boiling water decomposes them. It can also be prepared by adding ammonia to cold dilute zinc
chloride solution, by dissolving freshly precipitated zinc hydroxide in ammonium chloride, and by heating more highly ammoniated zinc chlorides. It
distils when heated into glassy, hygroscopic monammoniate, ZnCl2.NH4.
The last named is very stable under heat, and is produced when ammonia acts on hot zinc chloride. Water decomposes it into ZnCl2.2NH4 and an
oxychloride of zinc. "
which is perhaps much more than you ever wanted, or need, to know about ZnCl2.
[Edited on 5-9-2015 by AJKOER]
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