Preparation method of quetiapine fumarate impurity D

The invention discloses a preparation method of a quetiapine fumarate impurity D. The method is characterized in that 11-chlorine-dibenzo [b, f] [1, 4] benzothiazepines and piperazine are subjected to thermal reaction for 4 to 10 hours under a temperature of 105 to 115 DEG C by using xylene as a solvent and potassium iodide or sodium iodide as a catalyst in the presence of anhydrous potassium carbonate or anhydrous sodium carbonate, so as to obtain the quetiapine fumarate impurity D. With the adoption of the method, the yield is increased (not less than 85%), and the product purity is high (not less than 99.0%). The method ahs the advantages that the raw materials are easily obtained, the cost is low, the harm to environment is nearly avoided, the safety and reliability are ensured, the reaction time is short, the product is high in quality, the industrial wastewater is easily treated, and the wastewater almost has no bad smell.