[40007-00-9]  · C5H5Cl2N  · Chlorine-Pyridine  · (MW 150.01)

(mild oxidizing agent)

Physical Data: 1 white crystals that decomposed rapidly when the solvent (CCl4) was removed; mp <=47 °C.

Solubility: sol chloroform; insol carbon tetrachloride.

Form Supplied in: not commercially available.

Preparative Methods: although the chlorine-pyridine complex has been isolated,1 the reagent is more conveniently prepared in situ.2

Handling, Storage, and Precautions: the same precautions associated with the use of Chlorine (protective clothing, respirator) should be followed; use in a fume hood.

The chlorine-pyridine complex has been used for the oxidation of alcohols.2 Secondary alcohols are oxidized to ketones, while primary alcohols stop at the aldehyde stage. The faster rate observed for secondary alcohols (~20 min) vs. primary alcohols (~60 min) suggested that chlorine-pyridine might be useful in selective oxidations. In the oxidation of steroid diols and triols, chlorine-pyridine showed moderate to good selectivity (eqs 1-3).2 Other reagents have been shown to be superior in effecting similar transformations.3 However, these results may be misleading due to the problems that attend the oxidation of steroidal alcohols (axial vs. equatorial, adjacent to an angular methyl group, etc.). Thus chlorine-pyridine may be more selective than eqs 1 and 3 suggest. The usefulness of this reagent needs to be investigated further.

1. Williams, D. M. JCS 1931, 2783.
2. Wicha, J.; Zarecki, A. TL 1974, 3059.
3. For other reagents that show selectivity in the oxidation of alcohols, see: Siedlecka, R.; Skarzewski, J.; Mlochowski, J. TL 1990, 31, 2177, and references cited therein.

R. Richard Goehring

Scios Nova, Baltimore, MD, USA

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