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Mercury(II) fulminate
Chemical compound From Wikipedia, the free encyclopedia
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Mercury(II) fulminate is a primary explosive with the chemical formula Hg(CNO)2. When recrystallized from water it exists as the hemihydrate 2 Hg(CNO)2·H2O. The anyhydrous form is obtained by recrystallization from ethanol.[1]: F217 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.
![{\displaystyle {{\mkern {2mu}}{\vphantom {A}}_{\hphantom {}}^{\hphantom {-}}{\mkern {-1.5mu}}{\vphantom {A}}_{{\vphantom {2}}{\llap {\smash[{t}]{}}}}^{{\smash[{t}]{\vphantom {2}}}{\llap {-}}}\mathrm {O} {-}{\overset {+}{\mathrm {N} }}{\equiv }\mathrm {C} {-}\mathrm {Hg} {-}\mathrm {C} {\equiv }{\overset {+}{\mathrm {N} }}{-}\mathrm {O} {\vphantom {A}}^{-}}}](http://wikimedia.org/api/rest_v1/media/math/render/svg/e5b4c737194efea9f10f5a66166db4e708455571)
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.[4]
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.[1] 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.[5]
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Preparation
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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.[6][4] However, Johann Kunckel had discovered the compound more than a century before in the 17th century.[7] The crystal structure of this compound was determined only in 2007.[8]
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.[9]
Another preparation method is through reaction of the sodium salt of nitromethane with an aqueous solution of mercury(II) chloride (HgCl2) at 0 °C (32 °F) to form a white precipitate of mercuric nitromethanate. This is digested with warm, dilute hydrochloric acid (HCl) to produce mercury(II) fulminate.[1]: F219
Intermediates
The oxidation and nitration of ethanol with nitric acid proceeds through a multitude of intermediate compounds before reaching mercury fulminate; acetaldehyde (CH3CHO), nitrosoacetaldehyde (CH2(NO)−CHO), isonitrosoacetaldehyde (CH(=NOH)−CHO), isonitrosoacetic acid (CH(=NOH)−COOH), nitroisonitrosoacetic acid (C(NO2)(=NOH)−COOH), formonitrolic acid (O2H−CH=NOH), and fulminic acid (C=NOH) are first formed. The last reacts with mercury to produce the fulminate.[1]: F219
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Decomposition
The thermal decomposition of mercury(II) fulminate can begin at temperatures as low as 100 °C (212 °F), though it proceeds at a much higher rate with increasing temperature.[10]
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.[1]
A possible reaction for the decomposition of mercury(II) fulminate yields carbon dioxide gas, nitrogen gas, and a combination of relatively stable mercury salts.[citation needed]
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