A distillation method, comprising: introducing a raw material comprising compounds represented by Formulas 1 and 2 below and an isomer of the compound into a first supply port of a first distillation column, discharging the introduced raw material to each of a first top stream discharged from an upper section of the first distillation column, and first, second and third bottom streams discharged from a lower section of the first distillation column, introducing the first bottom stream into a second supply port of a second distillation column, discharging the stream introduced into the second supply port to each of a second top stream discharged from an upper section of the second distillation column; and fourth and fifth bottom streams discharged from a lower section of the second distillation column; heat-exchanging the second top stream with the third bottom stream; and isolating the compound represented by Formula 2 from the upper section of the first distillation column, and the compound represented by Formula 1 from the upper section of the second distillation column, wherein Equations 1 and 2 below are satisfied: wherein R 1 is a C 4 to C 12 alkyl group, and R 2 to R 4 are each independently hydrogen or a C 4 to C 12 alkyl group, R 5 is a C 1 to C 4 alkyl group, and n is 1 to 4; T t − 2 − T b − 3 ≥ 8 ° C, P 2 / P 1 ≥ 3.0, wherein T t-2 indicates a temperature of the second top stream, and T b-3 indicates a temperature of the third bottom stream, and P 1 indicates a pressure of the upper section of the first distillation column (kg/cm 2 g), and P 2 indicates a pressure of the upper section of the second distillation column (kg/cm 2 g). introducing a raw material comprising compounds represented by Formulas 1 and 2 below and an isomer of the compound into a first supply port of a first distillation column, discharging the introduced raw material to each of a first top stream discharged from an upper section of the first distillation column, and first, second and third bottom streams discharged from a lower section of the first distillation column, introducing the first bottom stream into a second supply port of a second distillation column, discharging the stream introduced into the second supply port to each of a second top stream discharged from an upper section of the second distillation column; and fourth and fifth bottom streams discharged from a lower section of the second distillation column; heat-exchanging the second top stream with the third bottom stream; and isolating the compound represented by Formula 2 from the upper section of the first distillation column, and the compound represented by Formula 1 from the upper section of the second distillation column, wherein Equations 1 and 2 below are satisfied: wherein R 1 is a C 4 to C 12 alkyl group, and R 2 to R 4 are each independently hydrogen or a C 4 to C 12 alkyl group, R 5 is a C 1 to C 4 alkyl group, and n is 1 to 4; T t − 2 − T b − 3 ≥ 8 ° C, P 2 / P 1 ≥ 3.0, wherein T t-2 indicates a temperature of the second top stream, and T b-3 indicates a temperature of the third bottom stream, and P 1 indicates a pressure of the upper section of the first distillation column (kg/cm 2 g), and P 2 indicates a pressure of the upper section of the second distillation column (kg/cm 2 g).