B.
2,2-(Trimethylenedithio)cyclohexanone. A solution of
3.02 g. (0.0200 mole) of freshly distilled 1-pyrrolidinocyclohexene,
8.32 g. (0.0200 mole) of trimethylene dithiotosylate4 (Note
2), and
5 ml. of triethylamine (Note
3) in
40 ml. of anhydrous acetonitrile (Note
4), is refluxed for 12 hours in a
100-ml., round-bottom flask under a
nitrogen atmosphere. The solvent is removed with a rotary evaporator, and the residue is treated with
100 ml. of 0.1 N hydrochloric acid for 30 minutes at 50° (Note
5). The mixture is cooled to ambient temperature and extracted with three
50-ml. portions of diethyl ether. The combined
ether extracts are washed with
10% aqueous potassium hydrogen carbonate solution (Note
6), until the aqueous layer remains basic to litmus, and with saturated
sodium chloride solution. The ethereal solution is dried over
anhydrous sodium sulfate, filtered, and concentrated on a rotary evaporator. The resulting oily residue is diluted with
1 ml. of benzene then with
3 ml. of cyclohexane. The solution is poured into a
chromatographic column (13 × 2.5 cm.), prepared with 50 g. of alumina (Note
7) and
3:1 cyclohexane–benzene. With this solvent system, the desired product moves with the solvent front; the first 250 ml. of eluent contains 95% of the total product. Elution with an additional 175 ml. of solvent removes the remainder. The combined fractions are evaporated, and the pale-yellow, oily residue crystallizes readily on standing. Recrystallization of this material from
pentane gives
1.82 g. (
45% yield) of white, crystalline
2,2-(trimethylenedithio)cyclohexanone, m.p.
52–55° (Note
8).