50 4 methyl 2 pentanone 50 acetic acid and after a half hour of operation in the 5 3 theoretical plate column to establish equilibrium a mixture containing 50 dmso 50 methyl isoamyl ketone at 85 u00b0 c and 20 ml min was pumped in the rectification was continued with sampling of overhead and bottoms after 1 2 hour the analysis is shown in table 3 and was 23 9 4 methyl 2 pentanone 76 1 acetic acid in the overhead and 8 8 4 methyl 2 pentanone 91 2 acetic acid in the bottoms which gives a relative volatility of 1 25 of 4 methyl 2 pentanone to acetic acid after one hour of continuous operation the overhead was 47 4 4 methyl 2 pentanone 52 6 acetic acid the bottoms was 21 7 4 methyl 2 pentanone 78 3 acetic acid which is a relative volatility of 1 25 the usefulness or utility of this invention can be demonstrated by referring to the data presented in tables 1 2 and 3 all of the successful extractive distillation agents show that 4 methyl 2 pentanone and acetic acid can be separated from their mixtures by means of distillation in a rectification column and that the ease of separation as measured by relative volatility is considerable without these extractive distillation agents little improvement will occur in the rectification column the data also show that the most attractive agents will operate at a boilup rate low.