The general procedure for the synthesis of 2-chloro-5,6,7,8-tetrahydroquinoline from 5,6,7,8-tetrahydro-2-quinolinone is as follows:
1. 20 g (0.134 mol) of 5,6,7,8-tetrahydro-2-quinolinone was added to a 250 mL two-necked flask with 28.8 mL (0.38 mol) of phosphorus trichloride (molar ratio 1:2.3) under dry conditions.
2. The reaction was rapidly stirred and heated to 135 °C and kept at reflux for 16 hours.
3. Upon completion of the reaction, the reaction mixture was cooled to 60-80 °C and then slowly poured under vigorous stirring into a 0.1% (W/V) sodium hydroxide solution pre-cooled to 0-5 °C to adjust the pH to 8.5.
4. Extract twice with 250 mL of dichloromethane at 0 °C and combine the organic phases.
5. Concentrate the organic phase by rotary evaporation to obtain the crude product.
6. The crude product was subjected to reduced pressure distillation at a pressure of 12-15 mmHg and the fractions with boiling ranges of 135-137 °C were collected to afford 20.3 g of colorless to pale yellow 2-chloro-5,6,7,8-tetrahydroquinoline liquid in 90% yield.
