Reaction SMILES: [CH2:1]([CH:3]([CH2:6][CH2:7][CH2:8][CH3:9])[CH2:4][OH:5])[CH3:2].[C:10]([OH:17])(=[O:16])[CH2:11][CH2:12][C:13]([OH:15])=O>>[C:10]([O:17][CH2:4][CH:3]([CH2:1][CH3:2])[CH2:6][CH2:7][CH2:8][CH3:9])(=[O:16])[CH2:11][CH2:12][C:13]([O:5][CH2:4][CH:3]([CH2:1][CH3:2])[CH2:6][CH2:7][CH2:8][CH3:9])=[O:15]
Reactant: O=C(O)CCC(=O)O
Reactant: CCCCC(CC)CO
Product: CCCCC(CC)COC(=O)CCC(=O)OCC(CC)CCCC
Temperature: 80 °C
Reaction time: 1 h

Procedure:
A four-necked flask (equipped with a stirrer, a thermometer, a Dean-Stark apparatus, and a nitrogen gas inlet tube) was charged with 2515 g (19.3 mol) of 2-ethylhexanol (manufactured by KANTO CHEMICAL CO., LTD.), 877 g (7.43 mol) of succinic acid (manufactured by Wako Pure Chemical Industries, Ltd.), and 14.1 g (0.0742 mol) of paratoluenesulfonic acid monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.), and the contents were allowed to react from a state of a pressure of 16 kPa and 80° C. to a state of a pressure of 12 kPa and 90° C. over 7 hours to distill off water. Thereafter, 32 g of KYOWAAD 500SH (manufactured by Kyowa Chemical Industry Co., Ltd.) was added thereto, and the mixture was stirred at a pressure of 4.0 kPa and 80° C. for 1 hour, and then filtered in vacuo. A four-neck flask (equipped with a stirrer, a thermometer, a distillation tube, and a nitrogen gas inlet tube) was charged with the filtrate, and the residual 2-ethylhexanol was distilled off by allowing the contents to react from a state of a pressure of 0.7 kPa and 95° C. to a state of a pressure 0.5 kPa and 185° C. Thereafter, 16 g of KYOWAAD 500SH was again added thereto, and the mixture was stirred at a pressure of 4.0 kPa and 80° C. for 1 hour, and then filtered in vacuo, to provide bis(2-ethylhexyl) succinate. Next, a four-necked flask (equipped with a stirrer, a thermometer, a dropping funnel, a distillation tube, and a nitrogen gas inlet tube) was charged with 467 g (1.36 mol) of the bis(2-ethylhexyl) succinate obtained, 250 g (2.36 mol) of diethylene glycol, and 2.2 g of a methanol solution containing 28% by weight of sodium methoxide (sodium methoxide: 0.011 mol) as a catalyst, and 2-ethylhexanol formed by the reaction was distilled off by allowing the contents to react at 110° C. while gradually dropping the pressure from 2.7 kPa to 0.9 kPa over 45 minutes. The residue was cooled to 80° C., thereafter 1953 g (5.70 mol) of bis(2-ethylhexyl) succinate and 5.0 g of a methanol solution containing 28% by weight of sodium methoxide (sodium methoxide: 0.026 mol) were again added thereto, and the pressure was gradually dropped while increasing the temperature, from a state of 110° C. and 0.8 kPa to a state of 158° C. and 0.4 kPa over 5.5 hours, to distill off 2-ethylhexanol formed by the reaction. The residue was then cooled to 80° C., and 10.5 g of KYOWAAD 600S (manufactured by Kyowa Chemical Industry Co., Ltd.) was added thereto, and the mixture was stirred at a pressure of 4.0 kPa and 80° C. for 1 hour, and then filtered in vacuo. The residual bis(2-ethylhexyl) succinate was distilled off from the filtrate by gradually dropping the pressure while increasing the temperature, from a state of 178° C. and 0.3 kPa to a state of 220° C. and 0.1 kPa over 4.5 hours, to provide a yellow liquid (ester compound I) at an ambient temperature. The amount of the catalyst used was 0.53 mol per 100 mol of the dicarboxylic acid ester.