NOVELTY - In separating crude 4 carbon (C) cut (I) containing butanes, butenes, buta-1,3-diene and small amounts of other hydrocarbons, including 4 C acetylenes (II), buta-1,2-diene and 5 C hydrocarbons (III), first extractive distillation column with (I) feed in middle below selective solvent (IV) feed gives vapor side stream, below (I) feed, of (II) in less than spontaneous decomposition concentration, butadienes, (III) and (IV), and top stream of components less (IV)-soluble than (II).    USE - The process is used for separating a crude 4 carbon (C) cut containing butanes, butenes, buta-1,3-diene and small amounts of other hydrocarbons, including 4 C acetylenes, buta-1,2-diene and 5 C hydrocarbons (all claimed), e.g. a crude 4 C cut from a naphtha cracker.    ADVANTAGE - The 4 carbon (C) acetylene components of 4 C cuts cause problems, as they can foul apparatus and there is also the risk of spontaneous decomposition over a wide range of concentrations. Separation and front end hydrogenation, in which 4 C acetylenes are converted to buta-1,3-diene in a first process stage, is useful but normally uses selective hydrogenation on heterogeneous catalysts, which are costly and often have a short life. The present process for front-end separation of 4 C acetylenes avoids these drawbacks. It is also economical and technically feasible.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of plant for separating 4 carbon (C) cut by extractive distillation.    First extractive distillation column (K I)    Second extractive distillation column (K II)    First side column (SK I)    Second side column (SK II)    Stream of crude 4 C cut (1)    Selective solvent streams (2, 14)    Stream containing 4 C acetylenes (3)    Sump stream, mainly of selective solvent (4)    Top streams (5, 9, 11)    Top stream containing acetylenes (6)    Sump stream containing selective solvent (7)    Uncondensed vapor fraction of top stream (8)    Side stream (10)    Sump streams (12, 13)    Raffinate 1 (15)    Crude buta-1,3-diene (16)