octyne

Octyne refers to any algebraically unsaturated hydrocarbon containing the formula C8H14 and possessing one or two carbon–carbon triple bonds. The simplest members are the terminal (1‑octyne, 2‑octyne, 3‑octyne) and internal (1,4‑octadiyne) alkynes, as well as the enyne variants that combine alkyne and alkene groups. The compound is part of the larger alkynyl family, which includes ten‑, twelve‑, and fourteen‑carbon analogues.

The most common isomer, 1‑octyne, is a colourless liquid with a mild odor that boils at approximately 34 °C. 2‑Octyne is similar in appearance but boils slightly lower, around 33 °C, while higher‑order isomers such as 3‑octyne are still liquids at room temperature. When cooled, some internal alkynes may solidify owing to increased crystallinity. The molecules are linear or slightly branched, giving them characteristic boiling points between 30 and 40 °C and densities near 0.82 g cm⁻³.

Commercial octynes are produced mainly by dehydrohalogenation of 1‑bromooctane or by cross‑coupling reactions such as the Glaser or Sonogashira couplings, which join two alkyne fragments. Laboratory-scale synthesis often uses the base-catalyzed elimination of β‑haloalkanes or the alkylation of acetylene with alkyl halides under phase‑transfer conditions.

Octynes undergo typical alkyne chemistry. Electrophilic addition reactions, such as halogenation or hydrohalogenation, convert the triple bond to the corresponding halide or dihaloalkane. Hydrogenation over metal catalysts yields the saturated octane. Nucleophilic additions, notably with organometallic reagents (e.g., Grignard or organolithium), afford homoallylic alcohols after protonation. In addition, alkynes participate in cycloaddition reactions such as the Diels‑Alder with dienophiles after activation.

These properties make octynes useful intermediates in the synthesis of fine chemicals, pharmaceuticals, and polymer additives. They also serve as model substrates for studying reaction mechanisms. Octynes can irritate skin and mucous membranes; adequate ventilation and protective equipment are advised during handling.