Crystal violet lactone

1255-69-2

1552-42-7

Example 1: 21.5 g (97.0% purity) of 2-[4,4'-bis(dimethylamino)diphenylmethyl]-5-dimethylaminobenzoic acid was added to a 500 mL three-necked flask, followed by 250 mL of deionized water. The resulting suspension was stirred with the addition of 21.5 g of activated carbon (Model: SHIRASAGI-C, manufactured by Takeda Chemical Industries) and 2.0 g of 49% NaOH aqueous solution. The reaction system was heated to 90-95°C and maintained in this temperature range. During the reaction, air was passed into the reaction system at a rate of 400 mL/min for 9 hours. Upon completion of the reaction, the reaction mixture was filtered while hot, the filter cake was collected and re-slurried with deionized water. 19.5 g of 36% HCl aqueous solution was slowly added to the slurried solution until the solid was completely dissolved. Subsequently, the activated carbon was removed by filtration. The pH of the filtrate was adjusted to 7.0 with 49% NaOH aqueous solution and crystals of the target product were precipitated. The crystals were collected by filtration, washed with cold water and dried under vacuum to give 20.1 g of 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide in 95.4% yield. Analyzed by HPLC, the by-product generation rate was 1.5% and the reaction selectivity was 98.4%.