# Chlorsulphonic Acid

1. Nov 22, 2004

### dextercioby

Hello,

I have a question.Can one (theoretically) obtain Chlorsulphonic acid by disolving chlorhydric acid into sulphuric acid like follows:
$$H_{2}SO_{4} +HCl=HSO_{3}Cl+H_{2}O$$.

If not,how can one obtain the Chlorsulphonic acid?

2. Nov 22, 2004

### chem_tr

It is not wrong, as hydrochloric acid is stronger than sulfuric acid, but dehydration spoils the logic behind this; so I recommend that you try thionyl chloride-mediated chlorination of sulfuric acid:

$$SOCl_2+HO-SO_2-OH \longrightarrow Cl-SO_2-OH + SO_2 + HCl$$

There are some alternatives to thionyl chloride, but this is the best. You may also use phosphorus trichloride (which gives phosphite acid, $H_3PO_3$) or phosphorus oxytrichloride (which gives phosphate acid, $H_3PO_4$), or even phosphorus pentachloride (giving phosphorus oxytrichloride and then phosphate acid), etc.

3. Nov 24, 2004

### dextercioby

Okay,thenx for the info provided.But yet,i have another question:
I remember that sulphuric acid's first acid constant is larger than the chlorhydric's one,and smaller than the ones by iodhydric acid,perchloric and permanganic acids.
So,that,but not only that,should make sulphuric acid stronger than the chlorhydric one,right??

4. Nov 24, 2004

### chem_tr

It is not correct. I am clearly sure that HCl is more powerful than H2SO4[\sub]. Oxygen does not readily give proton away; even if it is attached to an ametal like phosphorus or boron.

5. Nov 24, 2004

### dextercioby

You're right,i've searched through many textbooks upon the various theories for acids and bases,but the numbers,awkwardly,do not match.For instance,the numbers in "Lehrbuch der Chemie" (7 authors,VEB Deutscher Verlag fur Grundstoffindustrie,Leipzig,1971) are $$pK_{S} \sim -3$$ for the sulphuric acid for the reaction
$$H_{2}SO_{4}+H_{2}O\rightleftharpoons HSO_{4}^{-}+H_{3}O^{+}$$
,while for the hydrochloric one $$pK_{S} \sim -7$$,in between which there is a huge gap.In other books (French ones and Pauling's one) the gap between these numbers was smaller,but either way,they stated that the hydrocloric acid is stronger than the sulphuric one.The question ithat arises is this one;
If the hydrochloric acid is stronger than the sulphuric one,why does the chemical equilibrium in the reaction:
$$2NaCl+H_{2}SO_{4} \rightleftharpoons 2HCl+Na_{2}SO_{4}$$ shift leftwards,so that u cannot obtain sulphuric acid from hydrochloric acid and the sulphuric acid's salts???

Last edited: Nov 24, 2004
6. Nov 24, 2004

### chem_tr

The powerful the acid, the eager to be involved in reaction... It is just that simple, I think.

7. Nov 24, 2004

### dextercioby

It ain't that simple.Not only hydrochloric acid's stronger than the sulphuric one.Yet one cannot obtain sulphuric acid from its salts and a stronger acid.There has to be a deeper explanation...I am sure of it.
It's just that i don't see it...

8. Nov 24, 2004

### GCT

In response to the first post,

See if this makes sense to you, assuming that your proposed reaction takes place to a significant yield (relative to the dissociation reaction of each of the strong acids).......we have an acid solution, furthermore by adding sufuric acid (or vice versa) to the solution decreases its pH. It is essentially what your saying, I believe this will not happen. Remember that the acids in consideration have a very strong tendendcy to dissociate in water, increasing pH.