Fulminic acid, silver salt

Among other fulminates, the silver salt, (CNO)2Ag, is of some importance. It is prepared in a way similar to mercury fulminate, by the action of alcohol on a silver solution in nitric acid. Silver fulminate, however, is of little value as an explosive since silver is an expensive raw material. Detonators of silver fulminate were employed only in the Italian Navy. 

The first product of the oxidation of alcohol is acetaldehyde and an important end-product is fulminic add, which latter can, however, only be isolated if silver or mercury ions are present. With these ions it forms salts—fulminates—which are stable towards nitric add in them, it must be presumed, the linkage with the metal is homopolar and non-ionogenic, as in mercuric cyanide. The formation of fulminic acid takes place because the carbonyl group of the aldehyde confers reactivity on the adjacent methyl group which then forms a point of attack for the nitrous acid. The various stages in the process are indicated by the following formulae ... 

As shown in the introduction, the DNM anion can be regarded as a resonance stabilized, nonlinear planar pseudohalide, which forms an insoluble, highly explosive brownish silver salt upon addition of silver nitrate to an aqueous solution of 7. The DNM anion is related to the linear fulminate ion (CNO ) and can formally be regarded as the addition product of NO to fulminic acid (HCNO). Starting from CH4, NO containing nonlinear pseudohalides can be derived by successive substitution of H by NO, e.g. H3C(NO)/H2C(NO), H2C(N0)2/HC(N0)2 and HC(NO)3/C(NO)3, whereas the linear pseudohalide CNO is formally formed by replacing three H atoms by one NO unit and deprotonation. 

Silver fulminate is insoluble in nitric acid, and is decomposed by hydrochloric acid. It darkens on exposure to light. One liter of water at 13° dissolves 0.075 gram of the salt, and at 30° 0.18 gram. The double fulminate of silver and potassium, AgONOKONC, is soluble in 8 parts of boiling water. 

Wentrup, C. et ai, Angew. Chem. (Intern. Ed.), 1979, 18, 467 It explodes on rapid heating, like the 5-methyl analogue and the silver salt. See Fulminic acid(reference 2)... 

Dihalofuroxans are formed on dehydrohalogenation of dihaloximes and when halogens react with mercury or silver fulminates. Iodine with the silver salt of phenylnitrosolic acid gives diphenylfuroxan. Boron trifluoride in acetic anhydride reacts with 2-(ethoxycarbonyl-nitromethylene)thiazolidine to give diethoxycarbonyl furoxan. In each case nitrile oxides are likely or proven intermediates. 

CNO The isomeric fulminate ion, CNO (Figure 3-5), can be drawn with three similar structures, but the resulting formal charges are unlikely. Because the order of electronegativities is C < N < O, none of these are plausible structures and the ion is predicted to be unstable. The only common fulminate salts are of mercury and silver both are explosive. Fulminic acid is linear HCNO in the vapor phase, consistent with structure C, and coordination complexes of CNO with many transition metal ions are known with MCNO structures. ... 

Mercuric Fulminate.—The mercury and silver salts of fulminic acid are both detonating explosives the former being the one used in detonating caps. 

Dansi (23) criticized the scheme of Wieland (Vol. Ill, p. 135). He could not obtain fulminates of mercury and silver by acting with their nitrates on iso-nitrosoacetic acid. The salts of isonitrosoacetic acid did not yield fulminates wlicn acting with nitric acid (equations 5 -8, Vol, 111, p. 135). This casts some doubt on the accuracy of Wieland s scheme. 

The only other salt of fulminic acid which was in some limited use was silver fulminate. However it no longer seems to be in use, and other salts were also of no use. 

It explodes on rapid heating, like the 5-methyl analogue and the silver salt. See Fulminic acid(reference 2)... 

Fulminic Acid, C=N--OH.—Salts of this acid are obtained when nitric acid, alcohol, and mercury or silver are brought together in certain proportions. Mercuric fulminate, (CNO)2Hg, is prepared for use in percussion caps, which are used to explode gunpowder, dynamite, and other explosives. Free fulminic acid is a very unstable volatile liquid. It resembles closely hydrocyanic acid in odor and poisonous properties. 

Silver and silver salts Acetylene, oxalic acid, tartaric acid, fulminic acid, ammonium compounds... 

The structure of metallic salts of fulminic acid is usually presented by a Pauling-like structure with metal bonded to carbon [3, 20-22], This seems to be a reasonable assumption even though some authors published studies supporting bonding between metal and oxygen [23] or even the possibility of the existence of both of these forms [24], The issue still causes discussion and a report of a theoretical study [22] and X-ray analysis [21], supporting the bonding between metal and carbon, was recently published. The character of the metal to carbon bond of alkaline and thalhum fulminate is ionic, whereas fulminates of silver and mercury are covalent [20, 25],... 

Metallic fulminates (except mercury and silver) have never been practically used as explosives due to the difficulties with their preparation and generally low physical and chemical stability. However, the sodium salt can be used for many applications in organic chemistry. This salt is more suitable for this applicaticm than the more easily accessible mercury or silver salts due to their tendency to form complexes in solutions. For example, the sodium salt is useable in the preparation of free fulminic acid by acidification of its solution with dilute sulfuric acid [2]. 

Silver fulminate is dimeric and rather endothermic (A+361.5 kJ/dimol, 1.21 kJ/g). It is readily formed from silver or its salts, nitric acid and ethanol, and is a much more sensitive and powerful detonator than mercuric fulminate [1], The properties and applications have been reviewed [2],... 

According to Tscherniak methylnitrolic acid decomposes in water to give formic acid and N2O, while Wieland found that when methylnitrolic acid 02NCH=NOH is boiled in aqueous solution, with or without the addition of a mineral acid it yields formic acid, nitrous oxide and fuhninic acid, which is precipitated as the silver or mercuric salt if silver or mercuric nitrate is added to the above mixture (equation 9). The yield of fulminate is increased by the presence of mineral acid and by boiling, but it is also formed at ambient temperatures. 

The only directly accessible metal fulminates are those of mercury(II) and silver(I), very dangerously exposive solids obtained by the action of nitric acid and ethanol on the metals or their salts. Most modern preparations of fulminato complexes involve the conversion of a known amount of mercury fulminate into aqueous sodium fulminate by the action of sodium amalgam and ice-cold water the sodium fulminate solution is then allowed to react with the appropriate amount of a transition metal salt, and the resulting complex fulminato ion is precipitated as the salt of a large cation, most frequently Ph4As+ or R4N+ these are not explosive,4,35 Alkali and alkaline earth metal salts containing complex fulminato anions may be isolated from aqueous solutions, but they are reported to be as exposive as the binary silver and mercury fulminates, and are therefore usually avoided. 

Summary Silver fulminate is prepared in a similar fashion as the mercury salt by the addition of a hot nitrate acid solution upon ethyl alcohol. In this case, silver nitrate is dissolved in nitric acid, the mixture is then heated, and the ethanol dropped in. As the reaction proceeds, the silver fulminate will precipitate. It is then easily filtered-off, washed, and dried. Note Various modifications to this procedure exist. 

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