Organic Syntheses, CV 5, 791
Submitted by Carl R. Johnson and Jeffrey E. Keiser
1.
Checked by Wayland E. Noland, Leonard J. Czuba, and William E. Parham.
1. Procedure
In a
500-ml. round-bottomed flask equipped with a magnetic stirrer are placed
22.5 g. (0.105 mole) of powdered sodium metaperiodate and 210 ml. of water. The mixture is stirred and cooled in an
ice bath (Note
1), and
12.4 g. (0.100 mole) of thioanisole (Note
2) is added. The reaction mixture is stirred for 15 hours at ice-bath temperature and is then filtered through a
Büchner funnel. The filter cake of sodium iodate is washed with three
30-ml. portions of methylene chloride. The
water-methylene chloride filtrate is transferred to a
separatory funnel, the lower
methylene chloride layer is removed, and the water layer is extracted with three
100-ml. portions of methylene chloride. The combined
methylene chloride extracts are treated with
activated carbon (Note
3) and dried over
anhydrous sodium sulfate (Note
4). The solvent is removed at reduced pressure to yield
13.6–13.9 g. of a slightly yellow oil (Note
5) which crystallizes on cooling. The crude sulfoxide is transferred to a
25-ml. distillation flask with the aid of a small amount of
methylene chloride. After removal of the solvent, a pinch of activated
carbon is added to the distillation flask (Note
6). Simple vacuum distillation (Note
7) of the crude product through a short path still affords
12.7–12.8 g. (
91%) of pure
methyl phenyl sulfoxide, b.p.
78–79° (0.1 mm.), m.p.
33–34° (Note
8) and (Note
9).
2. Notes
1. The periodate oxidation of aryl sulfides to sulfoxides may be carried out at room temperature; however, an
ice bath is necessary to prevent overoxidation of dialkyl sulfides.
3. The checkers used
1 g. of activated carbon.
5. Gas-phase chromatography shows this crude material to be sulfide-free sulfoxide containing a small amount of
methylene chloride.
6. The simple technique of adding a pinch of activated
carbon to the distillation pot affords a more nearly colorless distillate.
7. No fore-run is observed other than a small amount of
methylene chloride which does not condense. The pot is taken nearly to dryness.
8.
Methyl phenyl sulfoxide is extremely hygroscopic. The melting point is best taken by rapid transfer of the easily supercooled oil to a melting-point capillary by means of a finely drawn pipet. The sealed capillary is then cooled to effect crystallization of the sulfoxide.
9. This procedure, with slight modifications depending on the physical properties of the sulfide and sulfoxide in question, has been used to prepare a variety of sulfoxides as illustrated by examples provided in Table I. In the case of very insoluble sulfides, co-solvents such as
methanol or dioxane may be employed. Very soluble sulfoxides are best isolated by continuous extraction with
chloroform or methylene chloride.
3. Discussion
4. Merits of the Preparation
The present procedure is a specific example of the method generalized by Leonard and Johnson.
8 The method employs extremely mild reaction conditions and affords high yields of sulfoxides (Note
9) free of contamination by sulfides or sulfones.
Sodium periodate is easily and safely handled; however, the higher cost of this reagent in comparison to certain other oxidants,
e.g.,
hydrogen peroxide, may prohibit its use in large-scale reactions.
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