Mercury(II) fulminate is an explosive with the chemical formula . When recrystallized from water it exists as the hemihydrate . The anhydrous form is obtained by recrystallization from ethanol.
Preparation
Mercury(II) fulminate is prepared by dissolving mercury in nitric acid and adding ethanol to the solution. Edward Charles Howard is credited with first preparing it in 1800. However, Johann Kunckel had discovered the compound more than a century before in the 17th century. The crystal structure of this compound was determined only in 2007.
Silver fulminate can be prepared in a similar way, but this salt is even more unstable than mercury fulminate; it can explode even under water and is impossible to accumulate in large amounts because it detonates under its own weight.
Another preparation method is through reaction of the sodium salt of nitromethane with an aqueous solution of mercury(II) chloride () at to form a white precipitate of mercuric nitromethanate. This is digested with warm, dilute hydrochloric acid (HCl) to produce mercury(II) fulminate.
It may be decomposed with relative safety by reaction with ten times its weight of 20% sodium thiosulfate solution. This may evolve some toxic cyanogen gas.