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MeSynth
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DRY HYDROGEN CHLORIDE GAS
Olah..
Standard method of producing HC is sulfuric acid on sodium chloride. When I do this I get foaming problems.
I remember doing an experiment where I poured sulfuric acid onto sodium hydroxide (crystals) in a glass I bought from goodwill. I placed a few table
spoons in the glass and then poured sulfuric acid on top and swirled with my bare hand.
As I thought about swirling it again it went off with a huge cloud of white gas shooting skyward.
All that was left was a white mass of sodium sulfate with residual sulfuric acid and a cracked glass due to the heat.
The amount of gas that was produced makes me think that this would be a good way to produce HC for experiments.
I haven't done this since due to the reaction this had on me. I did however try sulfuric acid on a sodium hydroxide solution. The reaction is instant
when the sodium hydroxide is in solution.
This produces HC right?
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MeSynth
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I was wrong! The cloud of gas was steam...
I found a better method of producing it though! Dehydration of HCL with calcium chloride. No foam will be produced I'm sure! PLUS calcium chloride is
cheaper than sulfuric acid and HCL can be found at home depot.
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bbartlog
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HCl plus CaCl2 is what I plan to use in making an HCl generator. However, I think that you want to have two compartments of CaCl2 - one that actually
mixes with the aqueous HCl and drives the HCl gas out of solution, and a second one (dry) that the gas passes through, to absorb moisture/steam. Even
then, you would want further drying (via H2SO4 or some such) if you needed *really* dry HCl. For my purposes (haloalkane synthesis from alcohols)
absolute dryness is not essential, though.
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redox
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1. Were you suggesting that sulfuric acid and sodium hydroxide produced hydrogen chloride?
H2SO4 + NaOH -/-> HCl + ????????????
Maybe I read your first post wrong, but... What?!
You corrected yourself, fine, but what were you thinking?
2. Also, why is the title in all caps? 
3. This shouldn't be posted in the organic chemistry forum. This should be in general chemistry or beginnings.
[Edited on 15-8-2011 by redox]
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chemx01
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Are you nuts?!
Mixing conc. H2SO4 with solid NaOH, what kind of idea is that??
I remebered about 6-7 years ago when I started being interested in chemistry I saw interesting experiment how HCl is mixed with NaOH and the resulting
solution is salty water which can be drunk.
Of course I tried with conc. HCl and solid NaOH, the effect was spectatular huge cloud os steam and NaOH sprayed everywhere, my father has fear of
chemistry ever since :-)
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MeSynth
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The "Molar mass" of calcium chloride is 110.98 g/mol and for water (H2O) it's 18.01528(33) g/mol. So this means that 110.98 grams of calcium chloride
(anhydrous) can absorb 18 grams of water. I forget how HCL works and there is no point in me trying because I can't find the info that I'm looking
for.
What I do know is that no mater what concentration I use a good rule to follow is 18 grams of HCL per 110 grams of calcium chloride. To prevent steam
and the need for a drying tube I could place the flask containing the calcium chloride in an ice bath and very slowly drip in the HCL but that will be
boring so I will use a drying tube.
(drying HC with oleum will not work)
Quote: Originally posted by redox  | 1. Were you suggesting that sulfuric acid and sodium hydroxide produced hydrogen chloride?
H2SO4 + NaOH -/-> HCl + ????????????
Maybe I read your first post wrong, but... What?!
You corrected yourself, fine, but what were you thinking?
2. Also, why is the title in all caps?
3. This shouldn't be posted in the organic chemistry forum. This should be in general chemistry or beginnings.
[Edited on 15-8-2011 by redox] |
This was posted without thinking very hard obviously. When I did the sodium hydroxide and sulfuric acid experiment a while back I searched online to
find out what happened and for a second last night I remembered reading that it was HC that was evolved. silly me.. How can HC be evolved when there
is no chloride to begin with. I may have remembered the experiment wrong however but this is not likely.
Sulfuric acid reacts instantly with sodium chloride right? If you replaced the sodium hydroxide in my first post with salt the results would not be
the same and would proceed slower. Correct?
[Edited on 16-8-2011 by MeSynth]
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MeSynth
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| Quote: Originally posted by bbartlog | HCl plus CaCl2 is what I plan to use in making an HCl generator. However, I think that you want to have two compartments of CaCl2 - one that actually
mixes with the aqueous HCl and drives the HCl gas out of solution, and a second one (dry) that the gas passes through, to absorb moisture/steam. Even
then, you would want further drying (via H2SO4 or some such) if you needed *really* dry HCl. For my purposes (haloalkane synthesis from alcohols)
absolute dryness is not essential, though.
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I never passed it through sulfuric acid as a second drying stage. I must try this now. As always when being told something I didn't know I had an
idea. After reading your post I had the idea to use oleum in the second drying stage. Crude oleum is easy and cheap to make and would totally own any
water that tries to pass through..
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Bot0nist
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How do you make your 'crude oleum" easily. Thermal decomposition of a sulfate salt and bubble SO<sub>3</sub> through
H<sub>2</sub>SO<sub>4</sub>?
[Edited on 15-8-2011 by Bot0nist]
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Bolt
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SO3 + HCl --> SO3HCl, aka chlorosulfuric acid.
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smaerd
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If you can't understand why sulphuric acid and sodium hydroxide will NEVER generate HCl gas, then do not attempt this...
edit - This should not be in organic? This should not be attempted by a beginner. There are already a lot of threads on this...
To make anhydrous HCl gas here is what I do. DO NOT DO THIS OUTSIDE OF A FUME-HOOD IF YOU LIKE YOUR LIFE AND THE METAL/ELECTRONTIC THINGS NEARBY.
I use a 500mL vacuum filtration flask with the bottom lined with CaCl2 granules(drive-way de-icer 99% CaCl2). I use the appropriate sized rubber
stopper, and drill a TINY hole in it with a drill-press on the frozen stopper. Then I insert an 18gauge syringe needle through the hole(which is hard
to do and should be making an air-tight fit).
I connect a hose to the vacuum out-let, and lead it through a gas-wash bottle. Once the apparatus is assembled and sealed properly, I place a 10mL
syringe body fixed with concentrated hydrochloric acid onto the needle. I then slowly add a couple mL's of HCl through the syringe into the flask, and
out comes very corrosive and dangerous gas.
Disassembly after the gas has been generated must be done with the utmost of care(goggles, gloves, respirator, fume-hood). Obviously there will be HCl
gas inside of the vacuum flask and tubing and wash bottle. If you needed me to tell you this, you should think harder...
The rubber stopper has started to ''deform''(not in a serious or un-managable way) and the needle will surely need replacement eventually. Though this
is a simple low-tek way, without the use of 24/40 ground glass addition funnels, flasks, a gas-outlet, etc.
This also works for CO2 gas(decent for a cheap, dodgy, ''inert atmosphere'' for some reactions), etc.
[Edited on 16-8-2011 by smaerd]
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Magpie
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| Quote: Originally posted by smaerd |
...Once the apparatus is assembled and sealed properly, I place a 10mL syringe body fixed with concentrated hydrochloric acid onto the needle. I then
slowly add a couple mL's of HCl through the syringe into the flask, and out comes very corrosive and dangerous gas. ....
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What you are saying is that
HCl (aq) +CaCl2 -----> HCl (g) + CaCl2*xH2O
correct?
Is this a superior method to that shown in Brauer where H2SO4 would be used in place of your CaCl2? Your apparatus is certainly simpler.
The single most important condition for a successful synthesis is good mixing - Nicodem
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bbartlog
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I'm guessing that Brauer's method results in somewhat drier HCl. So far as the reaction is concerned, CaCl2 tends to drive HCl out of solution even if
both are aqueous, i.e. this (mostly) works even if there is so much water present that you aren't forming a solid hydrate of CaCl2. Which should be a
caution for anyone who wants to build a Kipp-style generator based on the reaction... I believe that it would be easy to end up dissolving some CaCl2
and then ending up with a supersaturated solution of HCl that continued to evolve gas even after gas pressure had forced the liquid and solid apart.
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smaerd
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I can not say if it is superior to other methods or means, as this is the only way I have tried. It is kind of ghetto I have to admit but I don't own
a lot of nice equipment, at least not yet. Yes magpie that is what I am saying. If there are other products, I have no idea what they could even be
hehehe. edit - anhydrous CaCl2 when dissolved in water is pretty damn exothermic hence it's double use in drive-way de-icer(freezing point depression
as well).
It does release enough pressure to bubble cleanly for 20 minutes or so with a hose submerged completely in a 100mL edit - graduated cylinder filled to
the 100mL mark with distilled water(this is how I purify yellow dirty hard-ware store HCl for dilute solutions).
I have not witnessed suck-back, but I have only injected 5mL of conc. HCl at a time.After the bubbling has slowed to a minimal rate(A bubble every
minute or so), raise the tube out of the water to allow the pressure to equalize, remove the syringe(carefully) then reload it with more HCl(if more
gas is needed). Shake the filtration flask, so fresh dry CaCl2 can be put underneath the syringe, and it's good to go again.
The reason why I never tried the H2SO4 method was, why deal with two strong acids when you can deal with one? The downside is the syringe size
probably. So it's probably not practical for all applications(drying lewis acid hydrates under an HCl stream, etc).
If you would like I could take a photograph of it in action tomorrow?
edit - why would it be more dry? Couldn't someone fill the gas-wash bottle with a little conc. H2SO4 instead of CaCl2 to get an equivalent level of
dryness?
[Edited on 16-8-2011 by smaerd]
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Magpie
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Yes, post a picture, if convenient.
In the not too far distant future I plan to make some HSO3Cl, chlorosulphonic acid. For that I will need a stream of controlled, dry HCl.
The single most important condition for a successful synthesis is good mixing - Nicodem
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smaerd
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Ah, then this is likely not the set-up you're looking for but hell, I'll post a picture in-case it helps someone else out on a search or something.
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MeSynth
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The "Molar mass" of calcium chloride is 110.98 g/mol and for water (H2O) it's 18.01528(33) g/mol. So this means that 110.98 grams of calcium chloride
(anhydrous) can absorb 18 grams of water. I forget how HCL works and there is no point in me trying because I can't find the info that I'm looking
for.
What I do know is that no mater what concentration I use a good rule to follow is 18 grams of HCL per 110 grams of calcium chloride. To prevent steam
and the need for a drying tube I could place the flask containing the calcium chloride in an ice bath and very slowly drip in the HCL but that will be
boring so I will use a drying tube.
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MeSynth
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(drying HC with oleum will not work)
[Edited on 16-8-2011 by MeSynth]
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DJF90
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I have a paper describing this method. I'll post it up when I get home to my computer early next week.
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bbartlog
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| Quote: | | So this means that 110.98 grams of calcium chloride (anhydrous) can absorb 18 grams of water. |
It doesn't mean any such thing. CaCl2 can absorb more than one equivalent of water. Dihydrate, tetrahydrate, and hexahydrate all exist (others too
IIRC). Now, as it happens, I would expect that excess CaCl2 will help dry the evolved gas (aqueous HCl goes to the bottom, evolved gas has to pass
through granules of CaCl2 on its way out). So your rule of thumb is not a bad one, it's just not based on theory the way you seem to think.
Also, you don't need anhydrous CaCl2 for this.
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Lambda-Eyde
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See attachment
Attachment: A Convenient Way To Generate Hydrogen Chloride.pdf (868kB)
This file has been downloaded 2152 times
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Magpie
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Thanks for posting this, Lambda-Eyde. I was going to use the Brauer method but would have to cobble some glassware just to get the proper hydraulics.
This will be much easier.
And it is a good time of the year to buy CaCl2 prills as the swimming pool suppliers are, or soon will be, having their sales.
[Edited on 16-8-2011 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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MeSynth
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| Quote: Originally posted by MeSynth | | Quote: Originally posted by bbartlog | HCl plus CaCl2 is what I plan to use in making an HCl generator. However, I think that you want to have two compartments of CaCl2 - one that actually
mixes with the aqueous HCl and drives the HCl gas out of solution, and a second one (dry) that the gas passes through, to absorb moisture/steam. Even
then, you would want further drying (via H2SO4 or some such) if you needed *really* dry HCl. For my purposes (haloalkane synthesis from alcohols)
absolute dryness is not essential, though.
|
I never passed it through sulfuric acid as a second drying stage. I must try this now. As always when being told something I didn't know I had an
idea. After reading your post I had the idea to use oleum in the second drying stage. Crude oleum is easy and cheap to make and would totally own any
water that tries to pass through.. |
| Quote: Originally posted by bbartlog | | Quote: | | So this means that 110.98 grams of calcium chloride (anhydrous) can absorb 18 grams of water. |
It doesn't mean any such thing. CaCl2 can absorb more than one equivalent of water. Dihydrate, tetrahydrate, and hexahydrate all exist (others too
IIRC). Now, as it happens, I would expect that excess CaCl2 will help dry the evolved gas (aqueous HCl goes to the bottom, evolved gas has to pass
through granules of CaCl2 on its way out). So your rule of thumb is not a bad one, it's just not based on theory the way you seem to think.
Also, you don't need anhydrous CaCl2 for this. |
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Magpie
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Today I set up an HCl generator using the procedure cited above by Lambda-Eyde. I wanted to verify my equipment layout and see if I could determine
if the HCl was truly dry. The layout is shown in the picture below.
At first I just loaded the pot (500mL RBF) with 10g of CaCl2 and the P-E funnel with 10mL of muriatic acid. The condenser and 25mL receiver would be
used to collect any condensate. The 500mL 3-neck RBF is a suckback trap. The small beaker contains a couple inches of olive oil, used as a bubbler to
indicate the generation of gas.
The generator worked as advertised generating a slow and steady series of bubbles that turned a wet piece of pH paper red. I even reloaded it with a
second charge of CaCl2 prills and muriatic acid. Since I have an efficient fume hood HCl gas escaping from the bubbler and the reload was not even
noticed. I could see no condensate in the condenser and there was none in the receiver. Therefore the HCl gas does appear to be truly dry.
Something very puzzling does occur, however. When the muriatic acid is added a slight vacuum is created within the system. It even pulled olive oil
into the suckback trap a couple times when I added a lot of acid at one time. This vacuum disappears shortly and gas pressure and bubbling is
restored.
I don't know why the vacuum occurs temporarily upon addition of the acid. Does anyone?
The single most important condition for a successful synthesis is good mixing - Nicodem
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Dr.Bob
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Not sure about the vacuum occurs, that might be some trace of basic impurities in the CaCl2 reacting with the HCl at first. Even is there is only a
trace of CaOH or CaO, it would react fast with the HCl and might reduce the pressure. Also, if the reaction or HCl and CaCl2 was slightly
endothermic, that would cool the air in the flask and make a slight vacuum.
But mostly I wanted to remind everyone that chlorosulfonic acid will attack plastic, rubber and many other materials, so be careful with it,
especially don't try to ever use it in plastic syringes, they are likely to leak or fail and cause a bad accident. So good luck making it, but be
careful, it is nasty stuff. I have used it to make sulfonyl chlorides, and while it works OK, it is very dangerous to work with.
Bob
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watson.fawkes
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You're adding
aqueous HCl to an atmosphere that's (almost) entirely HCl, at least after it runs for a while. Even if it's azeotropic when you add it, it will still
dissolve more HCl in that environment. It's not mixed perfectly when you add it, so the dissolution will continue until ordinary steady-state
conditions are reestablished. The result is to reduce the partial pressure due to HCl, causing an overall pressure drop.
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