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Org. Synth. 1949, 29, 59
DOI: 10.15227/orgsyn.029.0059
ISOPRENE CYCLIC SULFONE
[Thiophene, 2,5-dihydro-3-methyl-, 1-dioxide]
Submitted by Robert L. Frank and Raymond P. Seven1.
Checked by A. E. Barkdoll and R. S. Schreiber.
1. Procedure
Caution! If peroxides are present in the isoprene, they should be destroyed by washing with 10% acidified ferrous ammonium sulfate before distillation.
A 600-ml. steel reaction vessel (Note 1) is precooled before loading by filling it between one-fourth and one-half full of methanol and Dry Ice. After removal of the methanol and Dry Ice, the autoclave is charged with 120 g. (176 ml., 1.76 moles) of isoprene (Note 2), 113 g. (80 ml., 1.76 moles) of liquid sulfur dioxide, 88 ml. of methanol, and 4 g. of hydroquinone. The vessel is sealed, heated slowly to 85°, and maintained at that temperature for 4 hours. It is then cooled, the sulfone removed, the bomb rinsed with methanol, and the combined product and washings are treated hot with 5 g. of Norite. The filtered solution is concentrated to a volume of 250–300 ml., and the sulfone is allowed to crystallize. The material is filtered and washed with 50 ml. of cold methanol. Recrystallization from methanol (20 ml. per 25 g. of sulfone) yields 140–150 g. of thick, colorless plates. Concentration of the mother liquors raises the total yield to 182–191 g. (78–82%) (Note 3), melting at 63.5–64° (Note 4).
2. Notes
1. A steel reaction vessel of the type used for high-pressure catalytic hydrogenations is satisfactory. The pressure generated is less than 200 lb. For smaller quantities a heavy glass tube can also be used with proper precautions.
2. Commercial isoprene, obtained from Phillips Petroleum Company, should be freshly distilled before use, in order to eliminate isoprene dimers and polymers which are likely to accumulate in storage. If peroxides are present, they should be destroyed before distillation of the isoprene by washing with 10% acidified ferrous ammonium sulfate. As an added precaution, the distillation flask should not be permitted to go dry.
3. The yield of the cyclic sulfone depends upon the purity of isoprene. In one experiment, the checkers obtained the sulfone in 86% yield, using freshly distilled isoprene of 99 mole per cent purity, while the yield fell to 77% with commercial isoprene which had been distilled and stored at 5° for 1 week before use.
4. The checkers consistently obtained a slightly higher melting point (uncor.) in the range 64.4–65.4°. The purified cyclic sulfone serves as an ideal intermediate for the preparation of extremely pure isoprene, since isoprene can be regenerated nearly quantitatively at 135–140°2 Other sulfones that can be prepared by this method and that are useful in the purification of dienes are those of butadiene, m.p. 65.5°,3 and 2,3-dimethylbutadiene, m.p. 135°3 The sulfone of piperylene is a liquid.4
3. Discussion
Isoprene cyclic sulfone has been prepared only from isoprene and sulfur dioxide.2,3,5
This preparation is referenced from:

References and Notes
  1. Work done under contract with the Office of Rubber Reserve, Reconstruction Finance Corporation.
  2. Frank, Adams, Blegen, Deanin, and Smith, Ind. Eng. Chem., 39, 887 (1947).
  3. Staudinger and Ritzenthaler, Ber., 68, 455 (1935).
  4. Craig, J. Am. Chem. Soc., 65, 1006 (1943); Frank, Emmick, and Johnson, J. Am. Chem. Soc., 69, 2313 (1947).
  5. Eigenberger, J. prakt. Chem., (2) 127, 307 (1930).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

Isoprene cyclic sulfone

sulfone of piperylene

methanol (67-56-1)

hydroquinone (123-31-9)

sulfur dioxide (7446-09-5)

Norite (7782-42-5)

butadiene (106-99-0)

ferrous ammonium sulfate (10045-89-3)

2,3-Dimethylbutadiene (513-81-5)

ISOPRENE (78-79-5)

Thiophene, 2,5-dihydro-3-methyl-, 1-dioxide (1193-10-8)