Nitroguanidine

Nitroguanidine[11] is used as an explosive propellant, notably in mixtures as the smokeless powder triple-base. The nitroguanidine reduces the propellant's flash and flame temperature without sacrificing chamber pressure.
Nitroguanidine exists in two forms: the α-form invariably results when guanidine nitrate is dissolved in concentrated sulfuric and the solution is poured into water. It is the form which is commonly used in the explosives industry. It crystallizes from water in long, thin, flat, fiexible, lustrous needles which are tough and extremely difficult to pulverize; when α-nitroguanždine is decomposed by heat, a certain amount of β-nitroguanidine is found among the products.

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Properties:
IUPAC NAME: 1-Nitroguanidine
OTHER NAME: Picrite
MOLECULAR FORMULA: CH4N4O2
MOLAR MASS: 104.07 g/mol
SHOCK SENSITIVITY: high
FRICTION SENSITIVITY: high
EXPLOSIVE VELOCITY: 7000 m/s

β-Nitroguanidine is produced in variable amount, usually along with some of the α-compound, by the nitration of the mixture of guanidine sulfate and ammonium suifate which results from the hydrolysis of dicyandiamide by sulfuric acid. Conditions have been found which have yielded exclusively the β -compound in more than thirty trials. It crystallizes from water in fernlike c1usters of small, thin, elongated plates; it is converted into the α-compound by dissolving in concentrated sulfuric acid and pouring the solution into water. Both α- and β-nitroguanidine, if dissolved in hot concentrated nitric acid and allowed to crystallize, yield the same nitrate, thick, rhomb-shaped prisms which melt at 147įC with decomposition. The nitrate loses nitric acid slowly in the air, and gives α-nitroguanidine when recrystallized from water. Similarly, both forms recrystallized from strong hydrochloric acid yield a hydrochloride which crystallizes in needles. These lose hydrogen chloride rapidly in the air, and give α-nitroguanidžne when recrystallized from water. The two forms are alike in all their chemical reactions, in their derivatives and color reactions.
Neither form can be converted into the other by solution in water, and the two forms can be separated by fractional crystallization from this solvent. They appear to differ slightly in their solubility in water: β-form appears to be the more soluble.
Many of the reactions of nitroguanidine, particularly its decomposition by heat and the reactions which occur in aqueous and in sulfuric acid solutions, follow directly from its dearrangement. Nitroguanidine dearranges in two modes, as follows:



In aqueous solution nitroguanidine dearranges in both of the above-indicated modes, but the tendency toward dearrangement is small unless an acceptor for the product of the dearrangement is present. It results that nitroguanidine is relatively stable in aqueous solution; after many boilings and recrystallizations the same solution final1y becomes ammoniacal. Ammonia, being alkaline, tends to promote the decomposition of nitroamide in aqueous solution. Also, because of its mass action effect, it tends to inhibit dearrangement in the second mode which produces ammonia. If nitroguanidine is warmed with aqueous ammonia, the reaction is slow. But, if it is warmed with water and a large excess of ammonium carbonate, nitrous oxide comes off rapidly, the ammonia combines with the cyanamide from the dearrangement, and guanidine carbonate is formed in practical1y quantitative amount.
Flashless colloided powder containing nitroguanidine produces a considerable amount of gray smoke made up of solid materials from the decomposition of the substance. The gases smell of ammonia.
Nitroguanidine decomposes immediately upon melting and cannot be obtained in the form of a liquid, as can urea and other substances which commence to decompose when heated a few degrees above their melting points. There is no doubt whatever that nitroguanidine is a cool explosive, but there appears to be a disagreement as to the temperature which it produces. A package of nitroguanidine, exploded at night by means of a blasting cap, produces no visible flash. If 10 or 15% of the substance is incorporated in nitrocellulose powder, it makes the powder flashless.
Vieille found that the gases from the explosion of nitroguanidine were much less erosive than those from other explosives of comparable force, and considered the fact to be in harmony with his general conclusion that the hotter explosives are the more erosive.