The mixture was warmed to 20 °C and stirred until the starting material was ≤1.5 area% by HPLC analysis (typically 2 h). The reaction mixture was then concentrated to ca. was added at the controlled temperature 15 to 30 °C. At the end of the addition the temperature was increased to 80 °C. The mixture was allowed to react at 80 °C until the starting material was ≤1.0 area% by HPLC analysis (typically 4 -7 h). The reaction was cooled to 20 °C and volatiles were removed under reduced pressure then CH2Cl2 [29.5 L] was added. Water [56.9 L] was added followed by sodium carbonate to reach pH = 7 to 8. The aqueous phase was discarded, and volatiles were removed under reduced pressure. Then 2-propanol was added [26. and heated to 50 °C for 2 h. Reaction was cooled to 20 °C over 3 h. The precipitated solid was filtered, and the cake was washed once with 2-propanol [5. . The wet cake was then dried at 50 °C under vacuum to afford 6.12 kg of 4-(1-chloro-4-methylpyrido Then a prepared solution of fumaric acid [2.40 kg, 20.2 mol, 1.0 equiv.] in 95% aqueous ethanol [52. was added dropwise. Crystallization was observed upon addition of the fumaric acid solution and stirring was continued at 75 °C for 2 h after the end of the addition. The reaction mixture was cooled to 20 °C over 4 h and then stirring was continued for 4 h at the same temperature. The suspension was filtered and the collected solid was rinsed with EtOH [23. .