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2.5.12 Sulphonation
Chapter 2
[6, Ullmann, 2001, 15, Köppke, 2000, 16, Winnacker and Kuechler, 1982, 46, Ministerio de
Medio Ambiente, 2003]
For environmental issues and treatment of waste streams, see Section 4.3.2.8.
The direct introduction of the sulphonic acid group to an aromatic system is one of the most
important reactions in industrial organic chemistry. It gives high yields under relatively mild
conditions and usually results in well defined derivatives. Arylsulphonic acids are used chiefly
as intermediates in the manufacture of dyes, insecticides, pharmaceuticals, plasticisers, optical
brighteners, etc. Among the typical raw materials are also halogenated compounds, thus
contributing to the AOX load of waste water streams.
Chemical reaction
Sulphonation is usually carried out with concentrated sulphuric acid in excess of
about 50 to 100 % or using oleum. Due to the fundamental rules of electrophilic aromatic
substitution, the product is a mixture of the target molecule and isomers. The reaction is
reversible, with the yield and isomer distribution depending on the reaction conditions (e.g.
temperature, removal of reaction water by azeotrope distillation or addition of thionyl chloride).
R
H
H 2SO 4
- H 2O
(Oleum)
Figure 2.25: Sulphonation of an aromatic system
SO 3H
Increased temperature and reaction water removal also favour the formation of sulphones as byproducts.
Depending on the reactants (aromatic, H2SO4, oleum) and temperature, the oxidative
effects of sulphuric acid or sulphur trioxide can lead to unwanted oxidation reactions.
Operations
Figure 2.26 shows a typical sequence of operations for sulphonation, possible input materials
and associated waste streams. The reaction is carried out at temperatures of about 60 to 90 ºC in
cast steel or enamelled steel vessels. The sulphonating agent is fed into the vessel, the aromatic
compound is then added, and the reaction is controlled by means of temperature profiles or
metering.
On completion of the reaction, the batch is transferred into water, which causes unconverted
aromatic compounds to be released. The dilute sulphonation mass is cooled, and the free acid is
separated by filtration. For further purification, recrystallisation may be necessary.
If the free acid is too soluble and isolation is not possible in this way, other techniques are
carried out, such as:
• salting out with sodium sulphate or sodium chloride
• temperature controlled crystallisation, or
• reactive extraction.
OFC_BREF Dezember 2005 59
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