30 g of chromium trioxide is dissolved in 60 mL of 20% HCl and cooled down to 0°C. Then with vigorous stirring, a slow addition of 24 mL of pyridine is started. The temperature is kept below 40°C. After the addition, the mixture is stirred for another 10 minutes and put it into a refrigerator for 3h. Then filtered, washed with cold water and dried.
Dissolving the chromium trioxide in the HCl
Addition of the pyridine
The dried product