Preparation of sulfonyl chlorydes and mechanism of preparation of tosyl chloride After searching about the preparation of sulfonyl chlorides, I couldn't find much. I found that for preparation of tosyl chloride, chlorosulfonic acid can be used, as in:



Can chlorosulfonic acid be used to prepare sulfonyl chlorides in general? What are some other ways to prepare sulfonyl chlorides? If there is any.

The other part of the question, I'd like to know how the mechanism of this reaction would work. Having the equilibrium of the reaction:

$$\ce{3 ClSO2(OH) &lt;=&gt; SO2Cl+ + 2 SO3Cl- + H3O+}$$

How exactly is the $\ce{SO2Cl}$ formed? I didn't quite understand how the $\ce{Cl}$ became a cation. Apparently the benzene attacks that cation in order to form the desired product.
The way to understand this is to think of the autoprotolysis of water:

$$\ce{H2O + H2O &lt;=&gt; H3O+ + OH-} \tag{1}$$

In general autoprotolysis can be represented in the following form (you can recover eq. (1) by setting $\ce{A} = \ce{OH}$):

$$\ce{HA + HA &lt;=&gt; H2A+ + A-} \tag{2}$$

Now set $\ce{HA}$ as $\ce{ClSO3H}$ (or $\ce{(HO)SO2Cl}$, for clarity) and you have

$$\ce{(HO)SO2Cl + (HO)SO2Cl &lt;=&gt; (H2O+)SO2Cl + ^-OSO2Cl} \tag{3}$$

The cation produced in eq. (3) fragments to give water and the reactive chlorosulfonyl cation:

$$\ce{(H2O+)SO2Cl -&gt; ^+SO2Cl + H2O} \tag{4}$$

The water in eq. (4) reacts with a third molecule of acid in an ordinary acid-base reaction:

$$\ce{H2O + (HO)SO2Cl -&gt; H3O+ + ^-OSO2Cl} \tag{5}$$

The combined equation you have is simply the sum of eqs. (3), (4), and (5).