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Fulminate of mercury

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Mercury(II) fulminate
O − − N + ≡ C − Hg − C ≡ N + − O − {\displaystyle {\ce {{}^{-}O-{\overset {+}{N}}#C-Hg-C#{\overset {+}{N}}-O^{-}}}} {\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}}^{-}}}
Names
IUPAC name
Mercury(II) fulminate
Systematic IUPAC name
Dioxycyanomercury
Other names
  • Fulminated Mercury
  • Bis(fulminato-kappaC)mercury
  • Knallquecksilber (German)
  • bis[(oxidoazanylidyne)methyl]mercury
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.010.053
UNII
  • InChI=1S/2CNO.Hg/c2*1-2-3; checkY
    Key: MHWLNQBTOIYJJP-UHFFFAOYSA-N checkY
  • InChI=1/2CNO.Hg/c2*1-2-3;/rC2HgN2O2/c6-4-1-3-2-5-7
    Key: MHWLNQBTOIYJJP-HZIBCBEIAJ
  • [O-][N+]#C[Hg]C#[N+][O-]
Properties
Hg(CNO)2
Molar mass 284.626 g·mol−1
Appearance Grey, pale brown, or white crystalline solid
Density 4.42 g/cm3
Melting point 160 °C (320 °F; 433 K)
Boiling point 356.6 °C (673.9 °F; 629.8 K)
slightly soluble
Solubility in ethanol soluble
Solubility in ammonia soluble
Explosive data[1]
Shock sensitivity High
  • 5 cm (2 kg weight, 20 mg, Bureau of Mines apparatus)
  • 4 in (1 lb weight, 30 mg, Picatinny Arsenal apparatus)
Friction sensitivity High (explodes with fiber & steel shoe tests)
RE factor 37% to 50% (Trauzl lead block)
Hazards[2]
GHS labelling:
GHS01: ExplosiveGHS06: ToxicGHS08: Health hazardGHS09: Environmental hazard
Danger
H200, H301, H311, H331, H373, H410
P201, P202, P260, P262, P264, P270, P271, P273, P280, P281, P301+P316, P302+P352, P304+P340, P316, P319, P321, P330, P361+P364, P372, P373, P380, P391, P401, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
4
1
4
170 °C (338 °F; 443 K)
0.02 mg/m3, 0.01 mg/m3 (TWA), 0.03 mg/m3 (skin, 15 minute) (STEL)
NIOSH (US health exposure limits):[3]
PEL (Permissible)
  • 0.01 mg/m3 (TWA, 8h)
  • 0.04 mg/m3 (ceiling)
REL (Recommended)
  • 0.01 mg/m3 (TWA, skin)
  • 0.03 mg/m3 (STEL, skin)
IDLH (Immediate danger)
 2 mg/m3 (as Hg)
Related compounds
Other anions
Other cations
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Mercury(II) fulminate is an explosive with the chemical formula Hg(CNO)2. When recrystallized from water it exists as the hemihydrate 2 Hg(CNO)2·H2O. The anhydrous 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.

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]

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.[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 

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.

4 Hg(CNO)2 → 2 CO2 + N2 + HgO + 3 Hg(OCN)CN
Hg(CNO)2 → 2 CO + N2 + Hg
Hg(CNO)2 → Hg(O−C≡N)2 or Hg(N=C=O)2
2 Hg(CNO)2 → 2 CO2 + N2 + Hg + Hg(CN)2

See also

References

  1. Fedoroff, Basil T.; Sheffield, Oliver E. (1 January 1974). "F". Encyclopedia of Explosives and Related Items (PDF). Vol. 6. Dover, NJ: Picatinny Arsenal. pp. F220-221. ADA011845, PATR2700. Retrieved 5 November 2025.
  2. Mercury(II) fulminate from PubChem
  3. "NIOSH Pocket Guide to Chemical Hazards".
  4. Wisniak, Jaime (2012). "Edward Charles Howard. Explosives, meteorites, and sugar". Educación Química. 23 (2). Universidad Nacional Autonoma de Mexico: 230–239. doi:10.1016/s0187-893x(17)30114-3. ISSN 0187-893X.
  5. Weingart, George W. (1947). Pyrotechnics (2nd ed.). p. 10. Retrieved 5 November 2025. Calomel [Hg2Cl2] is made in this country and sold in normal times at about 65 cents a pound, but due to the scarcity of mercury and the great demand for it in the manufacture of detonating caps the price has recently advanced to several dollars per pound.
  6. Edward Howard (1800). "On a New Fulminating Mercury". Philosophical Transactions of the Royal Society of London. 90 (1): 204–238. doi:10.1098/rstl.1800.0012. S2CID 138658702.
  7. "300 years after discovery, structure of mercury fulminate finally determined". Phys.org. August 24, 2007. Retrieved 19 February 2025.
  8. W. Beck; J. Evers; M. Göbel; G. Oehlinger; T. M. Klapötke (2007). "The Crystal and Molecular Structure of Mercury Fulminate (Knallquecksilber)". Zeitschrift für anorganische und allgemeine Chemie. 633 (9): 1417–1422. doi:10.1002/zaac.200700176.
  9. "The Sciences - Fulminating Substances". Scientific American. 11 June 1853.
  10. Garner, W. E.; Hailes, H. R. (1933). "Thermal decomposition and detonation of mercury fulminate". Proceedings of the Royal Society of London. 139 (1–3): 1–40. Bibcode:1933CP....334..128S. doi:10.1098/rspa.1933.0040.