Swarts reaction

What is Swarts reaction?

In 1892, Swarts (University of Ghent) was the first to report a reaction known as the Swarts reaction or Swarts fluorination. It involves the partial fluorination of nonpolar organic polyhalides, mostly aliphatic, using antimony trifluoride SbF3 with antimony pentachloride SbClor chlorine Cl2 present. The mixture of antimony trifluoride SbF3 and chlorine Cl2 is also called the Swarts reagent or Swarts mixture.

Swarts reaction - general reaction scheme - SbF3 and Cl2 - Swarts reagent - Swarts mixture
Swarts reaction

R = alkyl, aryl (see list of acronyms)

The Swarts reaction is a common exchange reaction between an organic halide and an inorganic fluoride, but it only occurs with activated organic halides.

The Swarts rule states that only aryl halides with more than one electron-withdrawing group on the aromatic ring can react with fluoride ion.

Swarts reaction is only partial, and it does not occur under reduced pressure. The resulting fluoride has a lower boiling point than the corresponding chloride, and each fluorine atom contributes almost equally to the decrement of boiling point, which is also known as the Swarts rule.

The chlorine atom attached to the atom rather than carbon can also be replaced by fluorine. For example, the chlorine attached to phosphorus or silicon can be replaced by fluorine.

References

  • Swarts, F., Bull. Acad. Roy. Belg., 1892, 24, 309
  • Swarts, F., Bull. Acad. Roy. Belg., 1892, 24, 474
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