Dimethylbutadiene

Dimethylbutadiene

Names
IUPAC name 2,3-Dimethyl-1,3-butadiene
Other names Biisopropenyl; Diisopropenyl; 2,3-Dimethylbuta-1,3-diene; 2,3-Dimethylbutadiene; 2,3-Dimethylenebutane
Identifiers
CAS Number	513-81-5
ChemSpider	10124
Jmol 3D model	Interactive image
PubChem	10566
InChI InChI=1S/C6H10/c1-5(2)6(3)4/h1,3H2,2,4H3 Key: SDJHPPZKZZWAKF-UHFFFAOYSA-N InChI=1/C6H10/c1-5(2)6(3)4/h1,3H2,2,4H3 Key: SDJHPPZKZZWAKF-UHFFFAOYAQ
SMILES CC(=C)C(=C)C
Properties
Chemical formula	C6H10
Molar mass	82.15 g·mol^−1
Density	0.7222g / cm^3[1]
Melting point	−76 °C (−105 °F; 197 K)
Boiling point	69 °C (156 °F; 342 K)
Vapor pressure	269 mm Hg (37.7 °C)
Hazards
Main hazards	Flammable and irritant
GHS pictograms
EU classification (DSD)	F Xi
Flash point	−1 °C (30 °F; 272 K) [2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Dimethylbutadiene, formally referred to as 2,3-dimethyl-1,3-butadiene, is an organic compound with the formula (CH₃)₂C₄H₄. It is colorless liquid which served an important role in the early history of synthetic rubber. It is now a specialty reagent.

Synthesis

Dimethylbutadiene is readily prepared by an acid catalyzed dehydration reaction of pinacol:^[3]

3 C₆H₁₄O₂ → C₆H₁₀ + 2 C₆H₁₂O + 4 H₂O

The current industrial route involves dimerization of propene followed by dehydrogenation.^[4]

Applications

In 1909, Fritz Hofmann and a team working at Bayer succeeded in polymerizing dimethylbutadiene. It was then called methyl isoprene because it has one more methyl group than isoprene. Their polymer was the first synthetic rubber.^[5] The polymer had a number of deficiencies relative to natural rubber.^[6] The Bayer synthesis of dimethylbutadiene involved the dehydration of pinacol, as described above.^[4]

Reactions

Dimethylbutadiene readily undergoes Diels-Alder reactions and reacts faster than 1,3-butadiene. Its effectiveness in this reaction is attributed to the stabilization of the cis-conformation owing to the influence of the methyl groups on the C2 and C3 positions.

Diels-Alder reaction using 2,3-dimethyl-1,3-butadiene and N-ethylmaleimide

References

1. Haynes, W. M.; Lide, D. R. (2012). CRC Handbook of Chemistry and Physics 93rd Ed. CRC Press/Taylor and Francis. ISBN 1439880492.
2. "CSID:10124". Retrieved 19 October 2012.
3. C. F. H. Allen, Alan Bell, L. W. Newton, and E. R. Coburn (1942). "2,3-Dimethyl-1,3-butadiene". Org. Synth. 22: 39.; Coll. Vol. 3, p. 312
4. Griesbaum, Karl; Behr, Arno; Biedenkapp, Dieter; Voges, Heinz-Werner; Garbe, Dorothea; Paetz, Christian; Collin, Gerd; Mayer, Dieter; Höke, Hartmut (2000), "Hydrocarbons", Ullmann's Encyclopedia of Industrial Chemistry (Weinheim: Wiley-VCH), doi:10.1002/14356007.a13_227.
5. The Moving Powers of Rubber, Leverkusen, Germany: LANXESS AG: 20.
6. "A Poor Substitute". Retrieved 18 October 2012.