Sulfonation

The sulfonation is a reaction in which a sulfonic acid group (-SO ₂ -OH group, and -SO ₃ H group), or sulfo group, in an organic compound is introduced. The reaction products are referred to as sulfonic acids , intermediate products can be sultones or anhydrides.

Sulphonations can take place on alkanes , alkenes or aromatics .

In contrast to sulfuric acid esters, the sulfur atom in sulfonic acids is bound directly to a carbon atom.

In general, one uses for sulfonation:

• Oleum in the sulfonation of aromatics such as benzene and toluene in the liquid phase
• Sulfur trioxide in the sulfonation of alkylbenzenes and olefins in the gas / liquid phase

A sulfo group can be introduced indirectly with

• Chlorosulfonic acid in the chlorosulfonation of aromatics
• Sulfur dioxide / chlorine gas mixtures in the radical sulfonation of alkanes , the so-called sulfochlorination

After hydrolysis and neutralization with ammonia or caustic soda , the products manufactured in the technical process are mainly used as surfactants in detergents and cleaning agents .

Sulfonation of aromatics

Synthesis of benzenesulfonic acid from benzene and conc. Sulfuric acid.

In the sulfonation of aromatics , the electrophile is sulfur trioxide (SO ₃ ) in sulfuric acid, pyridine or dioxane or the cation HSO ₃ ⁺ formed by protonation in sulfuric acid :

${\displaystyle \mathrm {SO_{3}+H_{2}SO_{4}\rightleftharpoons H_{2}S_{2}O_{7}\rightleftharpoons HSO_{3}^{+}+HSO_{4}^{-}} }$

The reaction can be accelerated if sulfur trioxide is dissolved in concentrated sulfuric acid ( oleum ). The sulfur trioxide is of decisive importance for the reaction, the sulfuric acid serves as the carrier medium for the sulfur trioxide. Sulfur trioxide proves to be a strong electrophile, as the sulfur atom is very positively polarized due to the strong electron pull of the oxygen atoms (electronegativity difference: 1.2).

Mesomeric boundary structures of sulfur trioxide .

The sulfonation reaction of aromatics is an electrophilic aromatic substitution .

All intermediate steps are reversible. The reaction with sulfur trioxide leads to the formation of a π and then a σ complex in which the aromaticity is canceled. The subsequent abstraction of a proton regenerates the aromatic system. The resulting product, the benzenesulfonic acid , can be treated with dilute sulfuric acid so that the sulfonic acid group is split off again. This mechanism then reacts according to the principle of ipso substitution ; the sulfonic acid group is also a good leaving group because of its high electrophilicity. Sulphonation with SO ₃ can also produce sulphonic acid anhydrides in a side reaction, which have to be hydrolyzed before the products can be further processed into surfactants. Further by-products can sulfones arise.

Sulfonation of alkenes

The sulfonation of alkenes provides a wide range of products from alkenesulfonic acids [α-alkene sulfonates (AOS)], 1,3- and 1,4-sultones, alkene disulfonic acids and sultone sulfonic acids.

In the formation of the sultones , a [2 + 2] cycloaddition of the S = O double bond of the SO ₃ with the C = C double bond of the alkene is assumed to be the first reaction step, which then leads to the 1,3- and 1,4 -Sultone forms. The sultones have to be hydrolyzed to surfactants before further processing of the AOS .

Chlorosulfonation of aromatics

A sulfo group can also be introduced indirectly via chlorosulfonation . Look there.

Sulfochlorination of alkanes

As sulfochlorination refers to the replacement ( substitution ) of hydrogen through the sulfonyl chloride group (SO ₂ Cl) in alkanes . This reaction is a radical substitution and is also known as the Reed reaction .

Individual evidence

1. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 5: Pl-S. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1987, ISBN 3-440-04515-3 , pp. 4053-4054.
2. ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 1366.
3. ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 1364.
4. ^ Author collective, Organikum , 16th edition, VEB Deutscher Verlag der Wissenschaften, Berlin, 1986, p. 307f.
5. ^ Hans Peter Latscha, Uli Kazmaier and Helmut Alfons Klein: Organic Chemistry . Springer, Berlin; Edition: 6th, completely revised edition 2008; ISBN 3-5407-7106-9 ; P. 112.

literature

• Peter Sykes: How do organic reactions work? 2nd edition, Wiley-VCH 2001, ISBN 3-527-30305-7
• Marye Anne Fox / James K. Whitesell: Organic Chemistry, Fundamentals, Mechanisms, Bioorganic Applications , Spectrum, Akad. Verl., 1995, ISBN 3-86025249-6
• Industrial organic chemistry: important preliminary and intermediate products, by Hans-Jürgen Arpe, 552 pages, Wiley-VCH; Edition: 6th, completely revised. A. (January 2007), ISBN 3527315403 , ISBN 978-3527315406 (as Google Book)