Mercury(II) fulminate
Mercury(II) fulminate is a primary explosive with the chemical formula Template:Chem2. When recrystallized from water it exists as the hemihydrate Template:Chem2. The anyhydrous form is obtained by recrystallization from ethanol.<ref name="EncycExplosives"/>Template:Rp It is highly sensitive to friction, heat and shock and is mainly used as a trigger for other explosives in percussion caps and detonators. Mercury(II) cyanate, though its chemical formula is identical, has a different atomic arrangement, making the cyanate and fulminate anionic isomers.
First used as a priming composition in small copper caps beginning in the 1820s, mercury fulminate quickly replaced flints as a means to ignite black powder charges in muzzle-loading firearms. Later, during the late 19th century and most of the 20th century, mercury fulminate became widely used in primers for self-contained rifle and pistol ammunition; it was the only practical detonator for firing projectiles until the early 20th century.<ref name=wisniak/>
Mercury fulminate has the distinct advantage over potassium chlorate of being non-corrosive, but it is known to attack aluminum and magnesium strongly, and brass, bronze, copper, and zinc slowly when dry; when wet it immediately reacts with aluminum and magnesium and strongly attacks brass, bronze, copper and zinc when.<ref name="EncycExplosives"/> Today, mercury fulminate has been replaced in primers by more efficient chemical substances. These are non-corrosive, less toxic, and more stable over time; they include lead azide, lead styphnate, and tetrazene derivatives. In addition, none of these compounds requires mercury for manufacture, supplies of which can be unreliable in wartime.<ref name="Weingart">Template:Cite book</ref>
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.<ref>Template:Cite journal</ref><ref name=wisniak>Template:Cite journal</ref> However, Johann Kunckel had discovered the compound more than a century before in the 17th century.<ref>Template:Cite web</ref> The crystal structure of this compound was determined only in 2007.<ref>Template:Cite journal</ref>
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.<ref>Template:Cite web</ref>
Another preparation method is through reaction of the sodium salt of nitromethane with an aqueous solution of mercury(II) chloride (Template:Chem2) at Template:Convert to form a white precipitate of mercuric nitromethanate. This is digested with warm, dilute hydrochloric acid (HCl) to produce mercury(II) fulminate.<ref name="EncycExplosives"/>Template:Rp
Intermediates
The oxidation and nitration of ethanol with nitric acid proceeds through a multitude of intermediate compounds before reaching mercury fulminate; acetaldehyde (Template:Chem2), nitrosoacetaldehyde (Template:Chem2, isonitrosoacetaldehyde (Template:Chem2), isonitrosoacetic acid (Template:Chem2), nitroisonitrosoacetic acid (Template:Chem2), formonitrolic acid (Template:Chem2), and fulminic acid (Template:Chem2) are first formed. The last reacts with mercury to produce the fulminate.<ref name="EncycExplosives"/>Template:Rp
Decomposition
The thermal decomposition of mercury(II) fulminate can begin at temperatures as low as Template:Convert, though it proceeds at a much higher rate with increasing temperature.<ref>Template:Cite journal</ref>
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.<ref name="EncycExplosives"/>
A possible reaction for the decomposition of mercury(II) fulminate yields carbon dioxide gas, nitrogen gas, and a combination of relatively stable mercury salts.Template:Cn