Preparation method of benzidine_Kain Industrial Additive

Background and overview^[1]

Toluidine can be used as a pharmaceutical synthesis intermediate.

Preparation^[1]

The specific steps for the preparation of benzidine are as follows: In a 500ml four-neck flask equipped with a thermometer, reflux condenser and stirrer, add 350g 30 mass% fuming sulfuric acid (1.31molSO3), and keep the internal temperature at 30°C to 40 ℃. At the same time, while paying attention to the generation of heat, 36.1 g (31.4 g, 0.148 mol, o-toluidine) of 13.1 mass % hydrous o-toluidine was added little by little. Excluding the amount of water decomposed, the molar ratio of sulfur trioxide to o-toluidine (sulfur trioxide/o-toluidine) is 7.1. Thereafter, the mixture was stirred at an internal temperature of 30°C for 30 minutes, further raised to 60°C within 30 minutes, and stirred at the same temperature for 2.5 hours. The reaction solution was cooled to 40° C. and poured into about 900 ml of ice water. The precipitated light brown crystals of o-triazine sulfate were collected by filtration. The crystals were added to 700 ml of water, further adjusted to pH 9 by adding 40 mass% sodium hydroxide aqueous solution, and heated to 90°C. The resulting crude crystals of free o-toluidine sulfone were collected by filtration. Crude o-tolylsulfone was added to 450 ml of water, 90 g of 36 mass% hydrochloric acid aqueous solution was added to form a hydrochloride salt, and the mixture was heated to 80°C and stirred for 1 hour. A 40% by mass sodium hydroxide aqueous solution was added to the solution to adjust the pH to 2, and the precipitated yellow crystals were collected by filtration. The crystals were washed with water and ethanol, and then dried under reduced pressure at 110° C. to obtain 38.4 g of benzidine. The yield is 94.6%. According to HPLC analysis, the purity of o-toluidine in this crystal is 99.5%, and the content of the impurity o-toluidine sulfonic acid is 0.12%. Sodium content is 52ppm.