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 Preparation of 2,3-Dimethyl-1,3-butadiene
  • Preparation of 2,3-Dimethyl-1,3-butadiene
  • 2,3-Dimethyl-1,3-Butadiene (CAS NO.: 513-81-5), which is also known as 1,3-Butadiene, 2,3-dimethyl-, could be produced through the following synthetic routes.

    Preparation of 2,3-Dimethyl-1,3-butadiene

    In a 2-l. round-bottomed flask, surmounted by a packed fractionating column, is placed a mixture of 354 g. (3 moles) of Pinacol and 10 ml. of commercial 48% hydrobromic acid. A few boiling chips are added, and the flask is then heated slowly with a colorless flame about 3 in. high. The distillate is collected until the thermometer reads 95°; this requires about 2 hours when the rate of distillation is approximately 20–30 drops per minute. The upper, non-aqueous layer is washed twice with 100-ml. portions of water, 0.5 g. of hydroquinone is added, and the liquid is dried overnight with 15 g. of anhydrous calcium chloride. It is then fractionated as below, using the same column but a 1-l. flask.


    Yield

    Fraction

    B.P.

    Grams

    Per Cent


    2,3-Dimethylbutadiene

    69–70.5°

    135–147

    55–60

    Intermediate

    70.5–105°

    10–15

    Pinacolone

    105–106°

    66–75

    22–25

    Residue

     

    7–8



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