The general procedure for the synthesis of 2,4-dichloro-7-methylquinazoline from 7-methylquinazoline-2,4(1H,3H)-dione was as follows: in a reaction flask equipped with a reflux condenser and a calcium chloride drying tube, 7-methylquinazoline-2,4(1H,3H)-dione (233 g, 1.32 mol) and phosphoryl chloride (500 mL, 5.23 mol) were added, followed by 25 mL of N,N-dimethylaniline was added. When gas production stopped (after about 30 minutes), the reaction mixture was heated to reflux overnight. Upon completion of the reaction, the dark solution was cooled to room temperature and slowly poured into 4 L of ice water. The solution was slowly added to the ice-water mixture under vigorous stirring and ice was replenished at appropriate times to maintain the temperature below 5 °C. The cooled suspension was extracted with dichloromethane (2 x 1 L). The organic phases were combined, washed sequentially with water and saturated sodium chloride solution (0.5 L), dried over anhydrous sodium sulfate and filtered. The organic layer was filtered through a silica gel plug and the filtrate was collected. The filtrate was concentrated to half the original volume, 0.5 L of heptane was added to each portion of the concentrate and evaporation was continued until crystals began to precipitate. The mixture was cooled to 5 °C and the precipitated solids were collected by filtration to give two 2,4-dichloro-7-methylquinazolines: 123 g (44%) off-white solid and 79 g (28%) yellow solid.
