hippo
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Alkyl Chloride preparation without anhydrous zinc chloride?
Is the presence of zinc chloride absolutely necessary for forming R-Cl from R-OH and HCl? I have been meaning to prepare n-Butyl Chloride and all the
preparations I've seen require anhydrous zinc chloride which I don't currently have access to.
Also, is it necessary for the ZnCl2 to be anhydrous? Can a hydrated form be used?
Regards,
hippo
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clearly_not_atara
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I really don't understand why you would need anhydrous ZnCl2 when you are going to drop it right into an aqueous solution. Seems pretty silly to me. I
think the real goal is just to decrease the water content of the rxn mixture as much as possible. This can be accomplished by adding zinc metal to
hydrochloric acid and then passing additional HCl gas into the solution. HCl suitable for this purpose can be produced by the thermal decomposition of
hydrated zinc chloride, which reduces the precursor burden.
Or maybe you can just use zinc sulfate, which is easy to dry.
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hippo
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The Wikipedia article states that:
| Quote: |
Hydrochloric acid alone reacts poorly with primary alcohols and secondary alcohols, but a combination of HCl with ZnCl2 (known together as the "Lucas
reagent") is effective for the preparation of alkyl chlorides.
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Although it doesn't state what part it has to play, every preparation I have seen thus far has stated that you need ZnCl2 present for the HCl to react
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XeonTheMGPony
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Step one: Get galvanized pipe or nails
Step two: Add hydrochloric acid
Step 3: watch it fizz
Step 4: Isolate your fresh Zinc Chloride from any iron salts.
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hippo
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It needs to be anhydrous I think
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Sigmatropic
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Simply refluxing butanol with HCl or in aqueous HCl is not going to afford butyl chloride. The affinity of water, or butanol, for HCl is simply too
low. This means the concentration of Cl- is nowhere near high enough to establish a favorable equilibrium between butyl alcohol and butyl chloride.
Certain Lewis acids are usually employed to aid this. Zn is typically used but I don't see why Fe or Al wouldn't work.
The chlorides of these materials do not necessarily have to be anhydrous as they are added to concentrated but still aqueous HCl. Instead their
oxychlorides may be employed. These oxychlorides are usually poorly defined and are thus not encountered in scientific literature. These oxychlorides
are, however, obtained when one dries the aqueous chloride salts to (almost) dryness.
So no it does not need to be anhydrous yet the synthesis will not work when it is omitted entirely.
Good luck and report your findings!
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hippo
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Thanks Sigmatropic!
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Melgar
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Butanol forms an azeotrope with water that's about 50/50, so you should just be able to boil a solution of ZnCl2, water, and butanol, until
chlorobutane starts coming over with it. Then just redistill whatever you collect. The chlorobutane should be the lowest-boiling component by quite
a lot.
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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unionised
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Chlorobutane and water will definitely form an azeotrope. That will have a lower boiling point than either component.
It''s possible that a ternary azeotrope will form with an even lower BP.
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MeshPL
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In the Vogel's Handbook of Practical Organic Chemistry (7 or 5ed., I don't remember) you can find a procedure for cyclohexyl chloride from
cyclohexanol, HCl and CaCl2. The zinc is therfore not necessary for some alcohols, but 1-butanol may need it as it is primary. I think that zinc may
increase the amount of Cl- in solution as ZnCl2 to move the reaction forward is insanely soluble in water: 432g per 100g of H2O.
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zed
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Well, if copper doesn't interfere, the U.S. penny might be a good source of Zinc.
Modern pennies are 97.5 % Zinc. Copper plated, they are.
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ninhydric1
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You can always melt the penny and remove then remove the copper casing using a gas burner or even a kitchen stove. The zinc will drip out of the
casing if you scratch or rub the copper layer off the penny.
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A Halogenated Substance
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For the exact mechanism for ZnCl2 helping the reaction, on the 11th page of this pdf, it shows ZnCl2 as attaching to
the oxygen of the alcohol and helping it become a much better leaving group.
https://crab.rutgers.edu/~alroche/Ch11.pdf
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SWIM
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Quote: Originally posted by MeshPL  | In the Vogel's Handbook of Practical Organic Chemistry (7 or 5ed., I don't remember) you can find a procedure for cyclohexyl chloride from
cyclohexanol, HCl and CaCl2. The zinc is therfore not necessary for some alcohols, but 1-butanol may need it as it is primary. I think that zinc may
increase the amount of Cl- in solution as ZnCl2 to move the reaction forward is insanely soluble in water: 432g per 100g of H2O.
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I've seen this reaction described in later sources as the 'exceptional behavior' of cyclohexanol as opposed to other secondary alcohols.
So I wouldn't count on it working for too many other secondary alcohols.
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byko3y
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Cyclohexanol can be converted into cyclohexyl chloride with concentrated HCl at room temperature with perfect yields (90%+). Usual secondary alcohol
require distillation temperature, large excess of azeotropic HCl-H2O, and still this yields only 50% of theory.
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SWIM
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| Quote: Originally posted by byko3y | | Cyclohexanol can be converted into cyclohexyl chloride with concentrated HCl at room temperature with perfect yields (90%+). Usual secondary alcohol
require distillation temperature, large excess of azeotropic HCl-H2O, and still this yields only 50% of theory. |
Thanks for the details.
Even with the low yield that's still an attractive sounding way to make isopropyl chloride given how cheap and easy to get the reagents are. (But I'd
certainly use the zinc chloride for more expensive alcohols)
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OrganoLeptic
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I can confirm that isopropyl chloride can be prepared from isopropyl alcohol with the use of 31% HCl(aq) and anhydrous CaCl2.
I got a 50 - 56% yield.
You can check out the video of the procedure here:
https://www.youtube.com/watch?v=KyeDmo0yOeA
I haven't yet used the isopropyl chloride I produced. But the boiling point of the product is in good agreement with the literature.
I don't know if this procedure would work for a primary alcohol.
I would be interested to hear if anyone had any success using HCl(aq)/CaCl2 on primary alcohols.
I will probably try it out myself in the next couple of weeks using a low boiling primary alcohol (probably n-propanol).
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byko3y
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You will not succeed with HCl+CaCl on saturated-chain primary alcohols. High pressure (2-5 atm) and high temperature needed.
Benzyl alcohol reacts with slight heating; activated benzyl alcohols e.g. methoxybenzyl easily reacts at r.t.; activated aliphatic primary alcohols
like ethylene glycol only slowly react at reflux temperature.
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OrganoLeptic
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Thank you byko3y. Do you know this from personal experience or from an article? I know it is somewhat common knowledge
that primary alcohols require more vigorous conditions. But that is part of the problem since it is difficult (at least for me)
to find any data on the issue. (+ people usually don't publish negative results)
My previous post does not reflect this but I also think that I will not succeed. That is why trying this out is of low priority.
The thing is, I was unable to find any data on anybody trying this with removing the product from the reaction mixture as it is formed.
I don't know if removing it by distillation even makes a difference. The solubility of the products (alkyl chlorides) is typically very low
and one could argue that the formation of a second layer is already removing the product from the reaction mixture and thus pushing the reaction
forward.
If that is the case, removing the product by distillation shouldn't really make much of a difference.
As far as I know the CaCl2 has no other function than to increase the concentration of chloride ions in the reaction mixture.
(If you have any data to the contrary I would like to hear about it.)
By this logic I would be content to see that someone tried to run the reaction with concentrated hydrochloric acid and removing
the product from the reaction mixture by distillation and failed miserably.
Byko3y if it isn't to much trouble I would also like to see a reference for the high pressure/high temperature
and the one for the activated aliphatic primary alcohols. I haven't seen any references like that, but I would like to.
Thank you.
[Edited on 7-9-2017 by OrganoLeptic]
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