Dimethylbutadiene

Dimethylbutadiene
Names
	Preferred IUPAC name 2,3-Dimethylbuta-1,3-diene
	Other names Biisopropenyl; Diisopropenyl; 2,3-Dimethylbutadiene; 2,3-Dimethylenebutane
Identifiers
CAS Number	513-81-5 ;
3D model (JSmol)	Interactive image;
ChemSpider	10124;
ECHA InfoCard	100.007.430
EC Number	208-172-0;
PubChem CID	10566;
UNII	61TUU25HCO ;
CompTox Dashboard (EPA)	DTXSID2022046 ;
	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	82.146 g·mol−1
Density	0.7222g / cm3
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
	Occupational safety and health (OHS/OSH):
Main hazards	Flammable and irritant
	GHS labelling:
Pictograms
Flash point	−1 °C (30 °F; 272 K)
	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]

HO(CH₃)₂C−C(CH₃)₂OH → CH₃(CH₂=C−C=CH₂)CH₃ + 2 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.

References

^ Haynes, W. M.; Lide, D. R. (2012). CRC Handbook of Chemistry and Physics 93rd Ed. CRC Press/Taylor and Francis. ISBN 978-1439880494.
^ "CSID:10124". Retrieved 19 October 2012.
^ C. F. H. Allen, Alan Bell, L. W. Newton, and E. R. Coburn (1942). "2,3-Dimethyl-1,3-butadiene". Organic Syntheses. 22: 39{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 3, p. 312.
^ ^a ^b 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, ISBN 3527306730.
^ The Moving Powers of Rubber, Leverkusen, Germany: LANXESS AG: 20.
^ "A Poor Substitute". Retrieved 18 October 2012.

[1] Haynes, W. M.; Lide, D. R. (2012). CRC Handbook of Chemistry and Physics 93rd Ed. CRC Press/Taylor and Francis. ISBN 978-1439880494.

[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{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 3, p. 312.

[Ullmann-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, ISBN 3527306730.

[5] The Moving Powers of Rubber, Leverkusen, Germany: LANXESS AG: 20.

[6] "A Poor Substitute". Retrieved 18 October 2012.

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