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2.5.14 Sulphochlorination with chlorosulphonic acid
[15, Köppke, 2000]
Chapter 2
Sulphochlorination leads to organic sulphochlorides, which act as intermediates for a variety of
fine chemicals, e.g. sulphonamides, sulphono hydrazides, sulphonic esters, sulphinic acids,
sulphones, and thiophenols.
Chemical reaction
Sulphochlorination takes place in a two step reaction as shown:
R
HSO 3Cl
SO 3H
R
(1) (2a)
Figure 2.30: Sulphochlorination with chlorosulphonic acid
HSO 3Cl
- H 2SO 4
OFC_BREF Dezember 2005 63
R
SO 2Cl
Step (1) represents a sulphonation similar to that described in Section 2.5.13. The reversible
second step is a chlorination and is usually carried out with excess chlorosulphonic acid.
Alternatively, thionyl chloride may be used for the second step as shown in the following
equation:
(2b) R – SO3H + SOCl2 � R – SO2Cl + SO2 + HCl
Side reactions:
• formation of sulphones (e.g. 35 % in the case of chloro benzene)
• formation of isomers
• formation of other halogenation products.
Operations
Figure 2.31 shows a typical sequence of operations in sulphochlorination.
The chlorosulphonic acid is introduced into a cast-steel or enamelled-steel vessel and
10 - 25 mol % of the aromatic compound is stirred in at 25 – 30 °C, whereupon sulphonation of
the aromatic compound and HCl formation occur. The exothermic formation of sulphonyl
chloride is initiated by heating the reactants to 50 – 80 °C.
In the case of aromatic compounds that easily take up two sulphochloride groups, e.g. anisole,
monochlorosulphonation is carried out with only a little more than the calculated amount of
chlorosulphonic acid at a low temperature (0 °C) and in the presence of a diluent such as
dichloromethane.
The temperature has to be controlled accurately to ensure the uniform release of HCl gas.
Restarting the agitator after an interruption of the electricity supply is hazardous and may cause
the contents of the vessel to foam over.