Sciencemadness Discussion Board - chlorosulfonic acid

chlorosulfonic acid

Magpie - 29-9-2011 at 13:16

Brauer (forum library) provides a method for making chlorosulfonic acid, HSO3Cl, by gassing oleum with dry HCl. A few days ago I did this but with poor yield. Earlier I assumed that the causes for this inefficiency were likely: 1) oleum too weak, and/or 2) HCl not dry enough. Yesterday I know I had very strong oleum (in solid form) and am very confident my HCl was dry. Still the uptake was very slow.

The CaCl2/muriatic acid method I used to generate HCl produces it at a very slow, even rate, ie, about 1 bubble/s. I think that this is part of the problem. At this rate the sparging goes on for hours. Also my sparge tube is only submerged about 8mm. I could solve these 2 problems with a different HCl production method and a better reaction vessel, ie, a long narrow vessel like a test tube. But I think that the main problem is just poor mass transfer. That is, the gas reacts slowly with the oleum.

Now one might say "well sure its going to react slowly with a solid." But this is the state of the oleum that both garage chemist and Peter (versuchschemie.de) used. I would ask Peter about this but I don't speak German. And garage chemist, unfortunately, does not visit this forum much anymore.

This brings me to Picric-A's statement of yesterday:

Quote: Originally posted by Picric-A

I have made chlorosulphuric acid in the past by slowly adding dry sodium chloride to <30% oleum and then distilling. This method is much easier than attempting to dry the HCl gas and can be a one pot reaction.

This is an intriguing method. Upon doing a little reading of a couple of my ancient texts I find that indeed at room temperature the following reaction should occur:

H2SO4 + NaCl ---> HCl + NaHSO4

I think that a key part of Picric-A's method might be that the NaCl is added slowly.

So, I would like to ask Picric-A to give us more details. What kind of equipment did you use? Did the NaHSO4 form a precipitate? If so, was this a problem for the distillation? What quantities were used. What was the yield?

[Edited on 29-9-2011 by Magpie]

AndersHoveland - 29-9-2011 at 13:31

The partial hydrolysis of sulfuryl chloride with water to form chlorosulfuric acid is usually described as:

SO2Cl2 + H2O --> HSO3Cl + HCl

However, one of the members in this forum has alerted me to the observation that chlorine gas seems to result when hydrochloric acid is added to 98 percent concentrated sulfuric acid. I cannot find anything in the literature about conc H2SO4 being able to oxidize HCl at room temperature, but it may be possible. If this is indeed the case, then the partial hydrolysis of SO2Cl2 with water might actually look like this:

(3)SO2Cl2 + H2O --> (2)HSO3Cl + SOCl2 + Cl2

and similarly, although the reaction of chlorosulfuric acid with water is usually described as
HSO3Cl + H2O --> H2SO4 + HCl, the actual reaction of chlorosulfuric acid with a limited quantity of water may look like this:

(2+2x)HSO3Cl + (2+x)H2O --> (2+x)H2SO4 + (x)H2O + (2)HCl + (x)SO2 + (x)Cl2

where x is some fractional molar ratio. water also appears in the reaction products side of the reaction, indicating that pure H2SO4 cannot result.

[Edited on 29-9-2011 by AndersHoveland]

garage chemist - 30-9-2011 at 08:11

I think that your problem is the unsuitable HCl generator.
I tried mixing CaCl2 and conc. HCl myself once and found it entirely worthless as a means of generating gaseous HCl for preparative work. Perhaps it has some value as a "new and safe" HCl generator for semi-microscale chemistry, but certainly not for macroscale preparations.

My favourite way of generating large amounts of gaseous HCl is as follows:
a length of glass tubing with drawn-out pipette tip is attached to the outlet of a pressure-equalized dropping funnel via a short piece of PVC tubing. The length of the pipette tube is such that the tip ends just above the bottom of the two-neck round-bottom flask that the dropping funnel sits on. The dropping funnel and the pipette tube are filled with conc. HCl, and the flask is filled halfway with conc. sulfuric acid.
The H2SO4 in the flask is heated to ca. 100°C, and the HCl is very slowly run in. Dehydration of the aqueous HCl by the H2SO4 is immediate and vigorous, and a brisk stream of HCl is withdrawn at the second neck of the flask and dried in a washing bottle with conc. H2SO4. About equal volumes of HCl and H2SO4 can be employed as reactants.
The bubbles in the washing bottle should be too fast to count.

This apparatus could be improved by using a peristaltic pump to pump the conc. HCl into the pipette tube which is attached to the H2SO4 flask via a quickfit. This would give perfect control over the gas stream, almost as good as with a compressed gas cylinder.

Another good method to generate smaller amounts of HCl gas is to mix equimolar amounts of solid NaHSO4 and NaCl in a flask and heat this directly with a bunsen burner. The mixture slowly reacts from the outside inwards since the reaction is endothermic. Removing the heat source soon stops the gas evolution.
The gas still has to be dried by a washing bottle of H2SO4.
Use a generous amount of NaHSO4 and NaCl since the reaction is not stochiometric and some dehydration of the NaHSO4 to pyrosulfate is unavoidable, evidenced by the water vapor evolution.
I would recommend this method for your setup, Magpie, since it is safer and easier to operate that the first method, which is only recommended for very experienced chemists and larger scale work.

The first method was inspired by the Orgsyn procedure for glycerol dichlorohydrin:
http://www.orgsyn.org/orgsyn/chemname.asp?nameID=33851

Quote:

The most convenient hydrogen chloride generator is that described by Sweeney.1 Concentrated hydrochloric acid is introduced into concentrated sulfuric acid by means of a dropping funnel and a capillary tube leading to the bottom of the sulfuric acid container. It is convenient to use a 3-l. bottle for this container and a 1-l. funnel to contain the hydrochloric acid. The gas is dried by passing through a wash bottle containing concentrated sulfuric acid. An empty catch-flask should be connected between the generator and the absorption flask in case any glycerol tends to suck back at the start of the reaction. About 6 kg. of concentrated hydrochloric acid and 10 kg. of concentrated sulfuric acid are required in one run. The generating flask will have to be recharged every six hours; it should be half filled with sulfuric acid. Aside from this, the apparatus needs no attention.

The reaction of HCl gas with strong oleum, solid or liquid, is immediate, quantitative and highly exothermic. The fact that you isolated unreacted SO3 strongly suggests that you didn't generate anywhere near enough HCl gas.

Magpie - 30-9-2011 at 10:10

Thank you garage chemist. I still have unreacted solid SO3 submerged in the reaction vessel. I will gas it using one of the methods you have described.

You probably already know this but the first method you describe is also shown nicely in Brauer.

Magpie - 30-9-2011 at 19:23

garage chemist, the NaHSO4/NaCl method you recommended did work well, providing a sizeable stream of HCl gas. The limiting factor was foam generation in my con H2SO4 absorber where a fritted sparge tube was used.

The gas stream was sparged into magnetically stirred oleum using a second fritted tube. This produced a continuous cloud in the reaction vessel. I presume this cloud was composed of very small droplets of chlorosulfonic acid. I continued until cloud production ceased.

It is interesting to note that a small chunk of asbestos-like solid SO3 never did fully dissolve.

Magpie - 1-10-2011 at 19:13

Here's the final result of my HSO3Cl synthesis. The yield was 25mL of crude HSO3Cl. Based on the amount of NaHSO4 used this is a 48.5% yield.

The first picture shows my HCl gassing setup using the CaCl2/muriatic acid method. This was later switched to a NaHSO4/NaCl method as recommended by garage chemist.

The 2nd picture shows the final distillation yielding the crude HSO3Cl.

The biggest part of this synthesis, IMO, is learning how to handle SO3 safely. It has many idiosyncrasies. Minimum safety gear is a good fume hood and a pair of nitrile gloves.

Thor - 2-10-2011 at 03:23

Can you comment on the kind of heat needed to produce the HCl gas using the NaHSO4 method? I had planned to use this method to make anhydrous AlCl3. As per the Benzene thread the dry distillation of salts ruined my glass flasks. So I was contemplating using a steel vessel. However im unsure how corrosive the HCl gas, and Bisulfate salt will be, especially at an elevated temperature. Also, congratulations on your synthesis of this obscure acid!

Magpie - 2-10-2011 at 07:53

Quote: Originally posted by Thor

Can you comment on the kind of heat needed to produce the HCl gas using the NaHSO4 method? I had planned to use this method to make anhydrous AlCl3. As per the Benzene thread the dry distillation of salts ruined my glass flasks. So I was contemplating using a steel vessel. However im unsure how corrosive the HCl gas, and Bisulfate salt will be, especially at an elevated temperature. Also, congratulations on your synthesis of this obscure acid!

Thanks Thor. garage chemist had made this acid sometime earlier and provided much help.

Per GC I mixed the NaHSO4 and NaCl powder dry in an equimolar ratio, using 100g of NaCl & some 200g or so of NaHSO4. This was probably way too much. The powder was placed in a 1000mL RBF, on an iron ring with a wire gauze. The flask was heated with a bunsen burner as required to generate a steady, prolific stream of gaseous HCl. The gas was sparged with a fritted glass tube into about 5cm of con H2SO4 to dry it.

Be aware that this will require a pressure of about 10cm H2O in the generation flask. I recommend that at least one greased, tapered glass joint be left unclamped as a safety pressure relief port in the event of overpressurization.

There was no damage to the RBF nor was any expected. In generating benzene I presume you used NaOH or other caustic material and this is known to damage glass when heated to fusion.

Thor - 3-10-2011 at 01:45

Quote: Originally posted by Magpie

Be aware that this will require a pressure of about 10cm H2O in the generation flask. I recommend that at least one greased, tapered glass joint be left unclamped as a safety pressure relief port in the event of overpressurization.

There was no damage to the RBF nor was any expected. In generating benzene I presume you used NaOH or other caustic material and this is known to damage glass when heated to fusion.

There was some visible corrosion to the glass, but in the case of Benzene i believe it is the way the melt contracts upon cooling, which causes the flasks to break. Although different salts will behave differently. However, thanks for the advice, a glass flask will be safer to use than a steel vessel.