The general procedure for the synthesis of 4,4'-methylenebis(2,6-diethylaniline) from 4,4'-methylenebis(3-chloro-2,6-diethylaniline) is as follows: 310 g (1 mol) of 4,4'-methylenebis(2,6-diethylaniline) (MDEA) was added to a three-necked flask fitted with a stirrer, thermometer and dropping funnel. At room temperature, 292.5 g (2.4 mol) of 30% hydrochloric acid solution was slowly added through the dropping funnel and stirred for 15 minutes until complete dissolution. Subsequently, 255.5 g (2.1 mol) of 30% hydrochloric acid solution was added, the reaction temperature was maintained at 45 °C and 262.3 g (2.7 mol) of 35% hydrogen peroxide solution was added slowly dropwise at this temperature and the dropwise process lasted for 2 hours. After completion of the dropwise addition, the reaction temperature was raised to 65°C and maintained for 1 hour. After completion of the reaction, the reaction mixture was cooled to below 10°C and left to stand for 10 hours. The solids and liquids were separated by pressurized filtration. The acidic mother liquor obtained from the separation was stored in an analytical grade vessel for subsequent synthesis of 4,4'-methylenebis(2,6-diethylaniline) (MDEA). The solid obtained by filtration was transferred to a three-necked flask and 200 g of water was added, followed by 280 g of 31% sodium hydroxide solution and stirred until neutralization was complete. After neutralization, the aqueous phase was separated by cooling, and the resulting solid was recrystallized from methanol using conventional methods to obtain white granular crystals, i.e., the target product 4,4'-methylenebis(3-chloro-2,6-diethylaniline). The purity of the product was analyzed by high performance liquid chromatography (HPLC) as 95.8%, in which 3,5-dichloro-4,4'-methylenebis(2,6-diethylaniline) was 0.5% and 3-chloro-4,4'-methylenebis(2,6-diethylaniline) was 1.3%. The above steps were repeated, the aqueous phase was separated after neutralization, the solid obtained was cooled and the fractions with boiling points of 245-250°C (fractions 7-8) were collected using a 30 x 0.5 magnetic ring distillation column. After distillation, the content of 4,4'-methylenebis(3-chloro-2,6-diethylaniline) was increased to 99.3% with a distillation yield of 95%, and this product can meet the demand of high-end polyurethane products.
