Synthesis of alkaline-earth metal picrates

Picric acid is known to react with metals to form highly unstable metallic picrates, which are known to have been involved in serious explosive accidents. In this study, alkaline-earth metal picrates of magnesium, calcium, strontium and barium salts are synthesized. Then, their thermodynamic and explosive properties such as initiation sensitivity are examined. The decomposition of alkaline-earth metal picrates begins at a higher temperature than that of picric acid. The heat of decomposition of alkaline-earth metal picrates was found to be lower than that of picric acid. Alkaline earth-metal picrates contain crystalline H2O, which dehydrates stepwise with increasing temperature. Experimental results show that the amount of crystalline H 2O in picrate in metastable phase is 9.2-9.9 H2O for Mg-picrate, 10.4-10.7 H2O for Ca-picrate, 5.0-5.1 H2O for Sr-picrate, and 5.9-6.4 H2O for Ba-picrate. However, the respective picrates changed to the stable form which contained the following amounts of crystalline water such as 6.5 H2O for Mg-picrate, 4.8 H2O for Ca-picrate, 4.0 H2O for Ba-picrate (Sr-picrate was not changed). The dehydration of crystalline water occurred between room temperature (about 298 K) and 480 K. Alkaline-earth metal picrates were dehydrated by heating in a vacuum at 473 K under 133 Pa. The activation energies at the initiation stage of exothermic decomposition are 125.6 kJ for Mg-picrate, 140.3 kJ for Ca-picrate, 171.3 kJ for Sr-picrate, and 257.7 kJ for Ba-picrate. Drop hammer test results show that Sr-picrate and Ba-picrate are more sensitive than picric acid.