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n‐Butyl mercaptane reacts with acetylene in the presence of [K(18‐cr‐6)SBu] as catalyst to give n‐butyl vinyl sulfide. In toluene the reaction is of zeroth order with respect to BuSH and first order with respect to [K(18‐cr‐6)SBu]. The reaction rate depends on the solvent in the following order: toluene > triglyme ≈ BuSH ≈ dioxane ≫ BuOH. In toluene, BuOH added in equimolar amounts accelerates the reaction indicating a complex formation [K(18‐cr‐6) (BuOH)SBu] with a higher catalytic activity. [K(18‐cr‐6)SBu] is monomeric in the solid state with d(K–S) = 3.051(2) Å. Potassium is displaced out of the mean plane defined by the six oxygen atoms of the crown ether by 0.626(3) Å. [K(18‐cr‐6)SBu] is a strong electrolyte in alcohols but practically no electrolytic dissociation takes place in solvents with low dielectric constants such as toluene and n‐butyl mercaptane. From the results a reaction mechanism is derived with the addition of non‐dissociated [K(18‐cr‐6)SBu] to acetylene as the rate‐determining step.