jwarr
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Anhydrous IPA + HCl
I'm trying to prepare an anhydrous IPA + HCl solution.
My current idea is generate HCl(g) by dripping a 34% aqueous solution of HCl over concentrated H2SO4. To get rid of the residual water in the gaseous
HCl I will be piping it through a drying tube filled with CaCl2 or CaSO4. The HCl(g) will be bubbled into anhydrous IPA stirring, on ice bath.
OK, so a couple questions here. First of all, any recommendations on which drying agent to use for the HCl(g) w/ residual H2O and IPA, which will
probably be obtained at 90 or 99%? Asuming the IPA is dried previously and stored properly, should the receiving flask be evacuated before starting
in order to prevent water from interfering at the time of the reaction? Am I missing anything blatantly obvious here?
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bbartlog
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How anhydrous do you want it? What are you trying to do?
MgSO4 would work as a drying agent for the IPA as long as you don't need it super dry.
I don't like the sound of your HCl gas scheme. You want to drip the HCl *on top* of the H2SO4? This will mean that as it is dehydrated, it will
evaporate at some point well before all the water is removed. At a minimum, I'd try to introduce it at the bottom of the denser H2SO4; however, even
this would probably result in some fairly wet bubbles of HCl+H2O gas. Unless H2SO4 is a scarce commodity for you, you could just go with NaCl+H2SO4 to
generate the HCl.
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woelen
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I think it is better to drip the conc. H2SO4 in the 34% HCl. The first few drops may only result in small amounts of HCl, but soon the reaction
proceeds smoothly. This is much safer than dripping 34% on conc. H2SO4. Such drops immediately cause boiling and splattering and formation of
excessive heat and you'll drive more water vapor out of the flask, together with the HCl.
I think that drying the HCl with CaCl2 is suitable. The IPA should be dried before HCl is bubbled into it. IPA can be dried with MgSO4 (anhydrous),
silica or molecular sieve (3A). After drying you can decant the liquid from the drying agent and the drying agent can be recovered by letting adhering
IPA evaporate and then heating. I'm not sure about suitability of CaCl2, it might be that this is somewhat soluble in IPA, please lookup info on that.
Sodium metal definitely should not be used, this reacts with IPA.
When the reaction is carried out, then all connections to the outside air (never build a completely closed system!!) should be through tubes with
CaCl2, such that moisture from outside air cannot enter the system. With such precautions you'll have almost perfectly dry IPA/HCl, but the last
traces of water may be hard to remove and each time you open that bottle in contact with air, new traces of water will get inside the bottle (you can
see this, the bottle becomes 'frosty' around the rim when it is opened, also a little bit inside). This is something which is really hard to prevent
when working with anhydrous HCl.
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bbartlog
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| Quote: | | I think it is better to drip the conc. H2SO4 in the 34% HCl. |
So this will actually work? Does it require aggressive stirring? Mentally, I'm picturing this as a situation where the H2SO4 removes water from the
HCl/H2O mixture, until the latter reaches a state where it has a high enough vapor pressure to gas off. And that point would be reached (at room
temperature) around the 50/50 mark, HCl and water.
However, if the H2SO4 and aqueous HCl are actually well mixed I can imagine that my mental picture is in error, since then the binding of the water by
the sulfuric acid would be something that happens everywhere at the same time, and in that case I could imagine dry HCl coming off while the water was
held back by the sulfuric acid.
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jwarr
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bbartlog,
I would like it very dry. This will be used to precipitate a salt of a weak organic base out of an organic solvent. Any water will obviously solvate
some of my product and ultimately lead to lower yields.
H2SO4 is not scarce by any means, but I would hate to be wasteful. How close is the yield w/ NaCl + H2SO4 to theoretical? Also, the literature I've
seen suggests the NaCl + H2SO4 method is much harder to clean up?
woelen,
would it be worthwhile to evacuate the system before beginning? I figure after that I could seal the system and not worry any pressure build up
beyond a significant percent of atmosphere.
[Edited on 12-2-2010 by jwarr]
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woelen
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I personally have done the dripping of H2SO4 in conc. HCl and this works smoothly after an initial period in which only small quantities of HCl are
formed. Of course the HCl produced in this way is somewhat humid. I did not drip HCl in conc. H2SO4 but the other way around. I only used occasional
swirling of the bottle with my hand. If you have a stirrer, then things become even better.
I also have made HCl from conc. hydrochloric acid and anhydrous CaCl2 and have reported on this method over here. This method works fairly well and
only requires the cheap and common CaCl2 besides conc. hydrochloric acid. The only problem is that the mix has a tendency of strong foaming.
I also have been playing around with NaCl/H2SO4 but I do not really like that reaction. It also has a very strong tendency of foaming and the reaction
soon becomes very slow after the first few percents of reactants have been used up. After that, you need heating.
If I were to do the making of HCl in IPA, then I don't think I would evacuate the system before starting the reaction. Just assure that the connection
with the outside air is through a tube of CaCl2 and you can slowly blow some air through that tube with a little pump in order to drive away the air
inside and replace that air with the dried air from the pump. So, you must have a setup with two tubes of CaCl2. One which is connected to the
receiving flask which contains the IPA in which the HCl is dissolved and the other between the HCl-gas generator and the flask with the IPA.
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bbartlog
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Small bubbles (as from a capillary tube) from below the surface make sense to me - even if the bubble has some H2O in it when first formed, the H2SO4
can remove that so long as the ratio of surface area to volume is large and the trip to the surface is long enough.
p 280 of Brauer also shows a capillary tube leading HCl to the bottom of H2SO4. Mind you, he then shows a *second* bottle of H2SO4 to dry the HCl
coming out of this arrangement. There's also a second arrangement that involves dripping both H2SO4 and HCl solutions into a tube filled with silica
or glass beads, which again seems to me to have the feature of allowing extended contact of the H2SO4 liquid with the HCl even after it passes into
the vapor phase.
Rather than achieve very dry HCl, it might be easier to accept some water mixed in with your HCl gas, and just dry the IPA with MgSO4 *after* you've
added the HCl. It shouldn't react.
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bahamuth
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I am in the same situation soon.
Also need it fairly dry. My route will be to dry the IPA with either CaO or small amounts of Na metal and distill it.
HCl gas generated by dripping sulfuric acid into fuming HCl and drying the gas with CaCl2 before bubbling this into the solvent worked well before,
but did not do it with IPA but Benzene or Xylene, cant remember, may even have been Toluene.
Also, had one cold finger in ice water before the CaCl2 drying, not sure if it helped alot, but IIRC some water droplets formed in the cold finger.
Remember ALOT of white noxious fumes when I did this before...
Hate to breath HCl gas, one of my least favorite things to do...
Any sufficiently advanced technology is indistinguishable from magic.
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Lambda-Eyde
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Pardon me for my lack of knowledge, but wouldn't HCl chlorinate IPA? Does this only happen in the presence of a lewis acid? Or does this only apply to
primary alcohols? (cf. EtOH + HCl in presence of ZnCl2)
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Sedit
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Chlorination as I understand it would proceed very slowly if at all without the presence of the catalyst.
The HCl generation scheem to me seems like its going to provide you with issues if dry is your goal. Might I suggest generating the HCl using NaCl
since you already have H2SO4 just drip this only NaCl that has been dampened with (aq)HCl and you will get HCl gas so dry that it can not be seen but
only in damn air. If you need it further dryed then run it thru a CaCl drying tube but I have always found it dry enough.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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jwarr
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Quote: Originally posted by bbartlog  | | Rather than achieve very dry HCl, it might be easier to accept some water mixed in with your HCl gas, and just dry the IPA with MgSO4 *after* you've
added the HCl. It shouldn't react. |
This was what I was hoping for, but I wasn't sure if there would be some sort of interaction between the drying agent and the HCl in solution. So I
should just be able to gas the semi-dry HCl into IPA and then dry with MgSO4, filter and finish?
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jwarr
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ah, so simple gravity filtration it is.
So, as it stands I believe I will be dripping conc. H2SO4 over HCl (aq), gas into 99% IPA. Dry IPA with MgSO4, gravity filter and we're done!
Any one see any issues with this? Ideas on theoretical efficiency?
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anotheronebitesthedust
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I've always preferred using both NaCl as well as 37% HCl. Just pour in HCl until the NaCl is completely covered, a bit extra HCl won't hurt, and use
an addition funnel to drip in H2SO4. There is no foaming and over time the NaCl slowly will disappear.
Use a ice water bath to keep the generator cool, and drierite drying tubes for inline drying. Even after multiple gassing sessions, I haven't needed
to regenerate the drierite yet, which goes to show that the gas is pretty damn dry. There's just a tiny bit of pink near the entrance to the tube.
http://www.drierite.com/catalog3/page7.cfm
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bbartlog
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| Quote: | | wouldn't HCl chlorinate IPA? |
Speaking as someone who has *tried* to chlorinate IPA with rather mixed results, I can assure you that this doesn't just happen by itself. At room
temperature and without a catalyst, there won't be a reaction.
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jwarr
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I could have swore I read somewhere that indicating drierite should not be used with HCl as there is some sort of reaction with the indicator. Am I
just imagining things here?
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Ozone
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The concentration of 2-chloropropane should be low (much tower than say t-butanol, which yields the corresponding chloro-compound at yields exceeding
85% at rt; 1<<2<3) at equilibrium.
Aside, we use acetyl chloride with methanol to make methanolic HCl (anhydrous). The corresponding amount of methyl acetate does not seem to interfere
with the behavior of the reagent wrt. methylating, say, fatty acids, etc.
I am not sure how IprOH will behave, in this case, but I'd expect the kinetics (addition of the -OH to the CO(H+)Cl, the acid supplies both the
nucleophile and the catalytic proton) to be much slower than with an unhindered primary hydroxyl (e.g. methanol).
Anyway, no water is introduced into the system.
[Edit]
In further investigation, I found the attached paper. Regardless of actual HCl/IprOAc yield, the material prepared from acetyl chloride was just as
effective a catalyst as that prepared using anhydrous HCl.
[Edit]
Cheers,
O3
[Edited on 13-2-2010 by Ozone]
Attachment: Esterification with Isopropanol_Frank et al 1979.pdf (199kB)
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