SSS rule

The SSS rule is a rule derived from observations for the regioselectivity in substitution reactions such as bromination or chlorination of alkyl- substituted aromatics such as toluene , ethylbenzene or xylene . It states that with alkyl-substituted aromatic compounds the reaction takes place under certain conditions on the side chain and not on the aromatic nucleus. The three S stand for S adiation (or S onne), S iedehitze and S eitenkette.

This can be deduced from the fact that radical substitutions on aliphatic compounds take place at high temperatures (the boiling point of many organic solvents such as toluene is 100 to 200 ° C) and under irradiation. Radiation, from the sun or a UV lamp, is necessary to form radicals . Aromatic rings are not attacked under these conditions.

S eitenkettenchlorierung of toluene at ≥ 110 ° C ( S iedepunkt of toluene: 110.8 ° C) induced by " S may light" (h · ν). The side chain is marked in blue .

The counterpart to the SSS rule is the KKK rule , which deals with electrophilic substitution on the aromatic ring itself, while aliphatic side chains are not attacked.

Individual evidence

1. ↑ Reinhard Brückner : reaction mechanisms . 3rd edition, Spektrum Akademischer Verlag, Munich 2004, p. 218, ISBN 3-8274-1579-9 .
2. ^ Siegfried Hauptmann : Organic Chemistry , 2nd edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, p. 297, ISBN 3-342-00280-8 .
3. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 3: H-L. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1983, ISBN 3-440-04513-7 , p. 2118.