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blogfast25
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Isopropyl chloride preparation question
I’ve just finished the first part of a 2-chloro propane preparation I found in a Google book.
It calls for refluxing for about 4 h of a mixture of 140 ml isopropanol (about 2 mol), 200 ml of 37 % HCl (about 2.4 mol HCl) and 100 g of anh.
ZnCl<sub>2</sub> catalyst. I halved everything and refluxed it in a 250 ml RBF with water cooled Allihn condenser for total reflux, for 4
hours. This is the part I just finished.
The preparation then calls for distilling the 2-chloro propane from the mix, followed by fractionation of that distillate for maximum purity.
What I don’t understand is, assuming the substitution reaction more or less took place, why doesn’t the 2-chloro propane just separate out, as it
is only very sparingly soluble in cold water? My reaction product mix certainly smells somewhat of chlorinated solvent and not much of HCl. The recipe
seems to imply that it shouldn’t separate out because there’s not a separation funnel in sight…
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deltaH
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...140 ml isopropanol... and 100g of anh. ZnCl2 "catalyst"
Hint hint, nudge nudge 
The numbers suggest stoichiometric amounts of catalyst was required which suggests stage one forms some stoichiometric intermediate adduct with
ZnCl2 that is soluble, maybe in equilibrium with the product in smaller amounts and the distillation drives it? From the masses, the ratio
of isopropanol to zinc chloride is exactly 2 on a mole basis, that's another suggestive clue IMHO.
[Edited on 20-4-2014 by deltaH]
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aga
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No idea, but here's a thread talking about it
Seems that some separation did happen for them.
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blogfast25
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delatH:
Maybe. I'm distilling tomorrow, so wait and see.
aga: no link?
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S.C. Wack
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The link works. Just no quote. Systematic Organic Chemistry used much less IPA and got separation. Any smell of IPA?
To a well-cooled mixture of 95 g conc. hydrochloric acid and 135 g anhydrous zinc chloride, 30 g isopropyl alcohol are added. The mixture is
vigorously boiled for 4 hours under reflux. The upper layer is separated after cooling, and gently boiled under reflux in a distilling flask with
closed side tube for 30 minutes. A condenser is attached to the side tube and the isopropyl chloride distilled. The distillate is washed with water,
dried over calcium chloride, and redistilled, the fraction boiling at 36-38° being collected separately.
Yield 70% (28 g). Colourless liquid; insoluble in water, bp 37°
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macckone
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Isopropyl chloride is soluble in Isopropyl alcohol.
If too much alcohol is left unreacted then the chloride
will probably not separate.
Also if your cooling is insufficient you will lose substantial
amounts of product. This reaction requires 0C or lower
cooling fluid for reflux.
FYI the zinc chloride need not be anhydrous, but you
have to use more by weight as you have to take into
account the water.
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blogfast25
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@SC Wack:
Thanks, didn't see that link. Orgie distilled first, that obtained separation, from what I understand.
I didn't smell any IPA but bear in mind there's an awful lot of water there.
I've this sinking feeling yield is going to be lousy.
@Macckone:
0 C cooling was not necessary: I used about 19 C water and noted no product loss. For the distillation I'll use about 5 C to cool the Liebig.
Using hydrated ZnCl2 introduces more water into the system, reducing the initial HCl concentration.
[Edited on 21-4-2014 by blogfast25]
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blogfast25
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Refluxing IPA, HCl and ZnCl2 (yesterday):
Simple distillation of refluxed reaction product mix:
The first product started coming over at about 30 C, so that was kind of promising. But temperature started climbing and climbing. At about 70 C there
seemed to be a plateau with distillate coming over at about 1.5 – 2 ml (based on drop count). And then it started climbing again and I stopped at
about 80 C. About 50 ml (visual guess) of distillate had been collected by then. No phase separation was observed, even though it was slightly milky.
I’m really not sure what to do next. Fractionating as the recipe called for would require a 100 ml apparatus which I don’t have. I guess I run a
few test tube tests.
Its odour does, subjectively of course, remind me of halo alkanes.
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macckone
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Quote: Originally posted by blogfast25  | @SC Wack:
Thanks, didn't see that link. Orgie distilled first, that obtained separation, from what I understand.
I didn't smell any IPA but bear in mind there's an awful lot of water there.
I've this sinking feeling yield is going to be lousy.
@Macckone:
0 C cooling was not necessary: I used about 19 C water and noted no product loss. For the distillation I'll use about 5 C to cool the Liebig.
Using hydrated ZnCl2 introduces more water into the system, reducing the initial HCl concentration.
[Edited on 21-4-2014 by blogfast25] |
Yes the 0C is not necessary but it is much easier to avoid product
loss if you use recirculating ice water. I am not saying you can't
use warmer water. In theory you can use water 2C less than the
BP of the product. In reality most people don't have a condenser
that efficient. One trick with this reaction is to hook up
a graham condenser and collect anything that escapes.
Allowing the chloride to escape and get condensed in the graham
during the reflux pushes the reaction to the right.
And yes non-anhydrous ZnCl2 introduces more
water into the system. But many people don't have anhydrous
ZnCl2. Bubbling HCl gas into the IPA instead of
of using concentrate HCl solution will also lower water content.
But my understanding is that a certain amount of water is
necessary to properly complex the ZnCl2 with the
IPA. I don't have the reaction mechanism in front of me but it
is ionic.
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S.C. Wack
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JACS 46, 753 (1924), claims 76% yield. Your book seems uninterested in following old literature. The ratio given here is the same used by OS (AV 5 pg
27) on other alcohols.
General Procedure.- A series of experiments with isoamyl alcohol led to the conclusion that the most satisfactory results were obtained when the
reaction was carried out with a mixture of the alcohol, concd. hydrochloric acid and zinc chloride in the molecular ratio of 1 to 2 (HCl) to 2,
respectively.
The method of procedure was the same in all cases except those noted below, and can, be illustrated by a description of an experiment with isoamyl
alcohol. One-quarter mole of the alcohol was used in each experiment. The weights in the case of isoamyl alcohol were alcohol 22 g., concd.
hydrochloric acid 47 g., anhydrous zinc chloride 68 g. The zinc chloride was dissolved in the cooled acid to prevent loss of hydrogen chloride; the
alcohol was then added and the mixture was refluxed for one hour. The mixture was then distilled as long as an insoluble oil passed over...
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macckone
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S.C. Wack,
That is an interesting link.
It implies that there are two mechanisms for forming the chloride.
The first when no water is present that has very low yield and
proceeds through dehydration and the second that involves
a ZnCl2 ionic complex of some kind. That has a higher
yield. The method described involves collecting product
without intermediate attempts to separate it.
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blogfast25
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| Quote: Originally posted by S.C. Wack | JACS 46, 753 (1924), claims 76% yield. Your book seems uninterested in following old literature. The ratio given here is the same used by OS (AV 5 pg
27) on other alcohols.
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Looks like I'll have to start all over again, this time using these alcohol/HCl/ZnCl2 ratios. It makes sense to have a much larger excess of HCl.
Does OS stand for 'org synth'? I'm not used to using that resource. Any chance you dig up that link? [Edit@ got it. For n-butyl]
@Macckone:
I don't have a Graham condenser but that set up could be achieved with an Allihn plus still head plus Liebig. I'll consider it. I like the idea of
pulling the equilibrium to the right.
[Edited on 22-4-2014 by blogfast25]
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S.C. Wack
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Wow, I looked at OS again and noted the date (1925) and everything else this time, and the references.
OS retroactively changed/deleted the entry, which was a submission from Norris checked by Marvel. Wow. That is not AV5, 27 (1925) at the site like it
says, it's CV1 142 (1941). Norris died in 1940. He's dead to OS, too. Wow.
"The method described above is based on a recently published study.4"
4. Whaley and Copenhaver, J. Am. Chem. Soc. 60, 2497 (1938).
Wow. OS says they have no preparations of isopropyl chloride. I wonder how many other deletions there are.
Since you can't get the original submission from the collective volume or the site, and it does include the isopropyl chloride that Whaley and
Copenhaver don't (OS was the reference for Cumming I posted first), here it is.
Attachment: os_5_27_1925.pdf (136kB)
This file has been downloaded 738 times
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macckone
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OK now I am glad I have files with the old OS infos.
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Magpie
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I looked for this prep in my Cumming (4th Ed), 1950. It's not there. I wonder why it was pulled?
The single most important condition for a successful synthesis is good mixing - Nicodem
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macckone
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The prep listed is driven to the right by distilling off the product.
I don't know why they don't include isopropyl chloride other than
they didn't do the experimental. I think it is wrong for them to
overwrite the reference lookup for vol 5 pg 27.
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blogfast25
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SC:
What I found at OS (AV 5 pg 27) is the n-butyl chloride prep, with reactive distillation.
The *.pdf you link to seems much older and relies only on refluxing, followed by separation and distilling the product over H2SO4.
My best bet (I think?) is to adapt the OS (AV 5 pg 27) prep for isopropyl chloride, with reactive distillation.
I’m really looking for just about any practical chloro alkane but a supplier let me down on t-butanol (for t-butyl chloride) and I don’t like
failure. So I’ll try and bite the bullet for the isopropyl chloride.
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S.C. Wack
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The sulfuric acid part of that in OS above was after the ... in the JACS article quote, which said it was not used in the case of isopropyl chloride.
In neither article did Norris really say there was two layers formed in the case of isopropyl chloride, Cumming just used the illustrated
experimental.
Is there a butyl or other chloride prep instead? There isn't in the 3rd. Vogel 3rd and 5th also used the original OS prep, just not for the propanols.
Presumably practical reasons rather than any kind of calling BS.
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Magpie
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Cumming's 4th has an ethyl chloride prep using ZnCl2, absolute ethanol, and gaseous HCl. Yield: almost theoretical. References are: A., 150, 216;
174, 372; Z. Ch., 1871, 147.
There are no propyl, iso-propyl, or butyl chloride preps.
The single most important condition for a successful synthesis is good mixing - Nicodem
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blogfast25
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58 ml of isopropanol (1.2 mol), 200 ml of HCl 37 w% (2.4 mol) and 332 mol of ZnCl<sub>2</sub> (anh.) (2.4 mol) were loaded into a 500 ml
round bottom flask (RBF) and connected to the set up below (bad photo, sorry!):
Left: sand bath with electrical hot plate, 500 ml RBF, Vigreux column 500 mm active length, still head with thermocouple.
Middle: Liebig condenser active length 400 mm with cooling circuit (about 10 C water temperature).
Right: 100 ml measuring cylinder, with iced water, acting as distillate receiver.
This ‘reactive fractionation’ went surprisingly smoothly and was over in less than 30 minutes. Distillate started coming over at 33.3 C and stayed
stable for quite a while, with distillate coming over too fast to count drops. All the while HCl fumes came over too (see Note 1).
About 20 minutes in head temperature started dropping slowly, distilling rate slowed down and eventually the flasks content more or less stopped
boiling altogether.
45 ml of distillate had been collected by then. This was worked up more or less (to scale) as OrgSynth’s preparation for n-butyl chloride but minus
the H2SO4 treatment (because I’m not sure what its purpose is). Two washes with 25 ml cold water, here’s what it looked like after the first one:
Clear separation between an organic phase and water can be seen. The wash water stank of chlorinated hydrocarbon, very similar to dry cleaning fluid
(perchloroethylene). Then I cooled the separation funnel again and washed with 6 ml of 10 % Na2CO3: a small amount of CO2 bubbles evolved.
The organic phase has now been placed in a Simax reagent bottle with 5 g of CaCl2 (anh.) in the refrigerator.
I have to decide now whether or not to distil this product. It’s intended for a Friedel Crafts alkylation of benzene (which I’ve yet to prepare!)
Any advice on further work up is welcome.
Note 1: the OrgSynth preparation called for a device to capture the HCl fumes. I didn’t bother with that and found good ventilation to be
sufficient. But considerable scale up would probably necessitate such a device. The OrgSynth preparation was for 5 moles of n-butanol.
Note 2: I had kept the distillate from the first run. Although it smells more faintly, its odour is very reminiscent of the distillate of this run. It
probably contains 2-chloropropane too, just much less.
[Edited on 27-4-2014 by blogfast25]
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deltaH
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Congrats and nice write up. Are you going to be making your own anh. aluminium chloride for your F-C alkylation?
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blogfast25
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| Quote: Originally posted by deltaH | | Congrats and nice write up. Are you going to be making your own anh. aluminium chloride for your F-C alkylation? |
Yes. I would like to test both homemade AlCl3 and SnCl4 as catalysts for FC alkylation. My first choice would have been t-butyl chloride but a
supplier let me down (on t-butanol). Hence the 'messing' with IPA. I'm waiting on some n-butanol, so I might try and chlorinate that as well.
[Edited on 26-4-2014 by blogfast25]
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Amos
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Thought I'd give this a try, but I wonder, do you absolutely require anhydrous zinc chloride? Couldn't one just use a hydrate formed easily from
hydrochloric acid and zinc metal, and just end up with a lower yield?
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DraconicAcid
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| Quote: Originally posted by Amos | | Thought I'd give this a try, but I wonder, do you absolutely require anhydrous zinc chloride? Couldn't one just use a hydrate formed easily from
hydrochloric acid and zinc metal, and just end up with a lower yield? |
You need the alcohol to coordinate to the zinc for the zinc to be catalytic; if there's water coordinated there already, the alcohol won't displace
it.
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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CuReUS
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here is a good link for preparing alkyl chlorides using TCCA
http://www.sciencemadness.org/talk/viewthread.php?tid=2726#p...
if you want to do an F.C,why not make the bromide instead. AlBr3 is easier to make compared to AlCl3
also,HBr(from NaBr) and H2SO4 is used to make alkyl bromides from alcohols .why cant HCl and H2SO4 be used
?
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