Dimethylbutadiene

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.

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
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.007.430
UNII
Properties
C6H10
Molar mass 82.146 g·mol−1
Density 0.7222g / cm3[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
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

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". Organic Syntheses. 22: 39.CS1 maint: multiple names: authors list (link); Collective Volume, 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.
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