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Mercury fulminate: structure, properties, obtaining, uses

It was discovered by the English empirical chemist Edward Howard in 1800. However, almost 200 years earlier it had been accidentally synthesized by the German alchemist Johannes Kunckel, who, due to the explosion that occurred, did not isolate it, but left written records of the ingredients used.

Crystals of fulminate of mercury Hg (CNO) 2 . Daniel Grohmann / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.

It is a primary explosive, so it is used in percussion or blast capsules to promote the explosion of other substances. Although its preparation and conservation is extremely dangerous, it was widely used in the 19th century as a detonator in war and hunting weapons.

It is currently used for the detonation of powerful dynamite charges in the construction of tunnels and roads and in mining.

It is clearly an extremely dangerous compound that can only be handled by people with deep knowledge of how to handle explosives.

Structure

Hg (CNO) 2 is a salt of fulminic acid HCNO. Contains mercury in oxidation state +2 and two CNO  fulminate units .

According to an X-ray study carried out in 2007 in Germany (reported in English in 2008), the molecules of mercury fulminate have the structure ONC-Hg-CNO, where it is observed that mercury is directly attached to carbon atoms .

The C-Hg-C bond is linear; It forms an angle of 180 ° and the fulminate group (CNO) has a short carbon-nitrogen bond and a longer nitrogen-oxygen bond.

The length of the CN bond is 1.14-1.17 Å (angstroms), which corresponds to a weak triple bond. The NO bond is 1.20-1.25 Å indicating a weak double bond. An angstrom (Å) is a measure of length and is one ten millionth of a meter.

Lewis structure of mercury fulminate. Benjah-bmm27 / Public domain. Source: Wikimedia Commons.

In the solid state, although the C-Hg-C junction is linear and the CNO group is also linear, the NC-Hg junction deviates from linearity by 11 °, that is, it has an angle of 169 °.

Hg (CNO) 2 molecule  in solid state. Gray = mercury; black = carbon; blue = nitrogen; red = oxygen. Benjah-bmm27 / Public domain. Source: Wikimedia Commons.

However, according to the aforementioned study, in the gaseous state the complete molecule is totally linear.

Nomenclature

  • Mercury fulminate
  • Mercuric fulminate
  • Mercury difulminate
  • Mercury bisfulminate
  • Mercury salt of fulminic acid
  • Withering mercury
  • Explosive mercury

Properties

Physical state

White to orange crystalline solid.

Hg (CNO) 2 wet solid. Daniel Grohmann / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.

Molecular weight

284.63 g / mol

Melting point

It does not melt. When heated to more than about 100 ° C it explodes.

Density

4.42 g / cm 3

Solubility

Slightly soluble in water. Soluble in ethanol (C 2 H 5 OH) and in ammonium hydroxide (NH 4 OH).

Chemical properties

It is a very explosive compound and highly sensitive to shock, impact or friction. It can be easily detonated with sparks and flames. When it decomposes it forms gases of mercury (Hg), carbon monoxide (CO) and nitrogen (N 2 ).

With concentrated sulfuric acid (H 2 SO 4 ) a violent detonation also occurs. Hydrochloric acid partially dissolves it and mercuric chloride is produced.

According to a study carried out in 1981, if it is subjected to controlled and very slow heating, under an inert argon atmosphere , when reaching 120 ° C a non-explosive decomposition occurs and solid mercuric oxide and mercury and oxygen gases are formed.

It is a compound that, due to its dangerousness, has been studied on few occasions and such study opportunities have been very far apart in time. Work must be done in the dark to avoid explosions. Your samples must be kept under water and without light.

Hg solid (CNO) 2 kept under water. Daniel Grohmann / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.

Obtaining

After its discovery, it was produced commercially through the reactions between ethanol (CH 3 CH 2 OH), mercury (Hg) and nitric acid (HNO 3 ).

In one of the most important studies on the structure of this compound, the researchers suggest that to obtain a higher yield during its preparation, the first half of the total volume of ethanol must be added to the mixture of Hg and HNO 3 before the gases brown color disappear.

In other words, it is important that nitrogen oxides are present for the reaction to proceed.

What happens first is the conversion of ethanol to acetaldehyde. According to certain studies, further oxidation, nitration, decarboxylation, and removal of nitrous acid then follow for the fulminate to form.

Use as a detonating agent for other explosives

War applications

Early attempts to use mercury fulminate as an explosive powder for firearms were thwarted by the extraordinary speed and violence of its detonation.

Pistols and shotguns were destroyed by small charges of this compound. The same happened with artillery pieces and grenades in military tests.

However, in 1822 the Englishman Wright used it for the first time as a firing pin in his sport hunting rifles. Later in Britain its use was implemented in infantry muskets and then throughout Europe.

In the 19th century, mercury fulminate was used as a detonator for many types of weapons of war. Author: Dimitris Vetsikas. Source: Pixabay.

Until the early 1900s it was the only detonator used to fire projectiles of any type, until other alternatives with safer and more accessible compounds were implemented.

Peaceful applications

This compound has played an important role in the development of explosives for peaceful purposes.

His role in the invention of dynamite by Alfred Nobel was very significant. This scientist combined nitroglycerin, a powerful explosive, with a porous material, diatomaceous earth. But the detonation of this mixture is difficult with sparks or fuses.

Nobel overcame this difficulty by using mercury fulminate firing cartridges that proved reliable in their application. This combination currently allows its use in mining, quarrying, tunnel construction and in civil engineering for the construction of roads, railways, ports, etc.

It has been widely used as an explosion detonator in mining and road construction. Author: Nyamdorj. Source: Pixabay.

Alfred Nobel himself emphasized the fundamental importance of mercury fulminate in the civil engineering developments that drove dynamite.

Risks

It is a very unstable and extremely explosive compound.

Author: Clker-Free-Vector-Images. Source: Pixabay.

Produces acute toxicity. It is toxic if ingested, inhaled or if it comes into contact with the skin. Easily causes contact dermatitis. It causes damage to internal organs if the person is exposed repeatedly or for a long time.

Very toxic to aquatic and terrestrial life with continuous long-term danger.

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