4-Octyne, also known as dipropylethyne, is a type of alkyne with a triple bond at its fourth carbon (the '4-' indicates the location of the triple bond in the chain). Its formula is C<sub>8</sub>H<sub>14</sub>.
4-Octyne forms with 5-decyne, 3-hexyne, and 2-butyne a group of symmetric alkynes.
One method for synthesizing 4-octyne is the reaction between acetylene and two equivalents of 1-bromopropane. Acetylene is first deprotonated by a base to give an anion, which then undergoes nucleophilic substitution with the bromopropane. The resulting alkyne is again deprotonated and reacts similarly with a second molecule of bromopropane. This reaction can be carried out in liquid ammonia at âÂÂ70 ðC with sodium amide as the base.
Another synthetic route is the elimination reaction of 4,5-dibromooctane, which can be done in similar conditions.
4-octyne is a colorless liquid at room temperature. Its density at 25 ðC and otherwise stable conditions is 0.751 g/mL. The boiling point is 131âÂÂ132 ðC. The average molar mass is 110.20 g/mol.