After a 2-minute time period, a small portion of oxalyl chloride (2.0 mL, 23 ) was added to a solution of 1,1,3,3-tetramethyl urea (2.5 mL, 21 mmol)/10 mL toluene
(2.0 mL, 23 mmol) to the oxalyl chloride (2.0 mL, 23 mmol) solution in 10 mL of toluene. After stirring for 18 hours at room temperature, the reaction mixture was concentrated under reduced pressure to a volume of about 5 mmol.
mL volume and the resulting precipitate was collected by filtration. The collected solid was dissolved in about 20 mL of water, followed by treatment with potassium hexafluorophosphate (3.8 g, 21 mmol)/50
mL of aqueous solution while the mixture was vigorously stirred at room temperature to obtain a white precipitate. The precipitate was collected by filtration and dried under vacuum. The solid was subsequently treated with about 8
mL acetone and filtered to remove insoluble material. The resulting filtrate was added in small portions to 60
mL of ether while stirring vigorously at room temperature. The desired product was collected by filtration and dried under vacuum to give 4.5 g (76 %) white solid.
