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MeSynth
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[*] posted on 14-8-2011 at 19:48
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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[*] posted on 14-8-2011 at 19:56


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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[*] posted on 14-8-2011 at 20:08


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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[*] posted on 15-8-2011 at 05:12


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? :mad:

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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[*] posted on 15-8-2011 at 08:35


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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[*] posted on 15-8-2011 at 09:14


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.

Quote: Originally posted by Bolt  
SO3 + HCl --> SO3HCl, aka chlorosulfuric acid.


(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? :mad:

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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[*] posted on 15-8-2011 at 09:25


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..
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[*] posted on 15-8-2011 at 09:38


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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[*] posted on 15-8-2011 at 10:08


SO3 + HCl --> SO3HCl, aka chlorosulfuric acid.
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[*] posted on 15-8-2011 at 17:25


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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[*] posted on 15-8-2011 at 17:59


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. ....


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.




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[*] posted on 15-8-2011 at 18:14


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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[*] posted on 15-8-2011 at 18:19


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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[*] posted on 15-8-2011 at 18:37


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.




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[*] posted on 15-8-2011 at 18:51


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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[*] posted on 15-8-2011 at 23:09


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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[*] posted on 15-8-2011 at 23:19


Quote: Originally posted by Bolt  
SO3 + HCl --> SO3HCl, aka chlorosulfuric acid.


(drying HC with oleum will not work)


[Edited on 16-8-2011 by MeSynth]
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[*] posted on 16-8-2011 at 05:38


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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[*] posted on 16-8-2011 at 05:44


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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[*] posted on 16-8-2011 at 05:54


See attachment

Attachment: A Convenient Way To Generate Hydrogen Chloride.pdf (868kB)
This file has been downloaded 1653 times





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[*] posted on 16-8-2011 at 08:49


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]




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[*] posted on 16-8-2011 at 09:34


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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[*] posted on 15-9-2011 at 10:32


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?



dry HCl generator.JPG - 103kB




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[*] posted on 15-9-2011 at 13:21


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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[*] posted on 15-9-2011 at 13:26


Quote: Originally posted by Magpie  
I don't know why the vacuum occurs temporarily upon addition of the acid. Does anyone?
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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