acetylenic hydrocarbons are removed from a c 4 - or c 5 - hydrocarbon mixture containing a c 4 - or c 5 - diolefin respectively . the feedstock is extractively distilled to remove paraffins and mono - olefins in the raffinate , using acetonitrile , dimethyl formamide , furfural , acetone , dimethylacetamide or n - methyl - 2 - pyrrolidone mixed with 0 - 12 weight percent water as the extraction solvent . the bottoms from this first extractive distillation is subjected to a second extractive distillation in which virtually acetylenes - free solvent is used . isoprene is withdrawn as the distillate with substantially reduced acetylenes content . the bottoms of the second extractive distillation is split three ways . two streams are handled conventionally . the third is stripped free of acetylenes so that it may be used as solvent in the second extractive distillation .