Nitrogen sulfide

Nitrogen sulfide[17] is a very unstable primary explosive compound. It is sensitive to heat, friction, shock, and will explode if heated over 160°C if impurities are present.
Nitrogen sulfide has many industrial uses, besides being used as a detonator. Some non-energetic uses of nitrogen sulfide are as an ignition promoter in diesel fuel, a component in pesticides and fungicides, and as an accelerator in rubber vulcanization.

IUPAC NAME: tetrasulfur tetranitride
MOLAR MASS: 184.29 g/mol

Nitrogen sulfide was first prepared by Soubeiran in 1837 by the action of ammonia on sulfur dichloride dissolved in benzene.
6 SCl2 + 16 NH3 ---> N4S4 + 2 S + 12 NH4Cl
It is conveniently prepared by dissolving 1 volume of sulfur chloride in 8 or 10 volumes of cabon disulfide, cooling and passing in dry ammonia gas until the dark brown powdery precipitate which forms at first has dissolved and an orange-yellow solution results which contains light-colored flocks of ammonium chloride. These are filtered off and rinsed with carbon disulfide, the solution is evaporated to dryness, and the residue is extracted with boiling carbon disulfide for the removal of sulfur. The undissolved material is crude nitrogen sulfide.
The hot extract on cooling deposits a further quantity in the form of minute golden-yellow crystals. The combined crude product is recrystallized from carbon disulfide. The same product is also produced by the action of ammonia on sulfur dichloride in carbon disulfide, benzene, or ether solution.
6 S2Cl2 + 16 NH3 ---> N4S4 + 8 S + 12 NH4Cl
Nitrogen sulfide has a density of 2,22 at 15°C. It is insoluble in water, slightly soluble in alcohol and ether, somewhat more soluble in carbon disulfide and benzene.
It reacts slowly with water at ordinary temperature with the formation of pentathionic acid, sulfur dioxide, free sulfur, and ammonia. It melts with saublimation at 178°C, and explodes at a higher temperature which, however, is variable according to the rate at which the substance is heated. Berthelot found that it deflagrates at 207°C or higher, and remarked that this temperature is about the same as the temperature of combustion of sulfur in the open air.
Berthelot and Vieille studied the thermochemical properties of nitrogen sulfide. Their data, recalculated to conform to our present notions of atomic and molecular weight, show that the substance is strongly endothermic and has a heat of formation of -138,8 calories per mol. It detonates with vigor under a hammer blow, but is less sensitive to shock and less violent in its effects than mercury fulminate. Although its rate of accelleration is considerably less than that of mercuri fulminate, it has been recommended as a filling for fuses, primers, and detonator caps, both alone and in mixtures with oxidizing agents such as lead peroxide, lead nitrate and potassium chlorate.

Nitrogen sulfide is stable to air. It is, however, unstable in the thermodynamic sense with a positive heat of formation of +460 kJ mol−1). This endothermic heat of formation anticipates its inherent instability, and originates in the difference in energy of S4N4 compared to its highly stable decomposition products:
S4N4 → 2 N2 + 0.5 S8
It is not really very unusual for complex molecules to be unstable in a thermodynamic sense yet stable kinetically; this situation describes many compounds. This combination of kinetic stability and thermodynamic instability is, however, uncommon for very simple compositions, such as sulfur nitride. Because one of its decomposition products is a gas, S4N4 is an explosive. Purer samples tend to be more explosive. Small samples can be detonated by striking with a hammer.
S4N4 is thermochromic, changing from pale yellow below −30°C to orange at room temperature to deep red above 100°C.

Nitrogen sulfide was prepared by the reaction of ammonia with SCl2 in carbon tetrachloride followed by extraction into dioxane.
6 SCl2 + 16 NH3 → S4N4 + S8 + 12 NH4Cl
A related synthesis employs NH4Cl in place of ammonia:
4 NH4Cl + 6 S2Cl2 → S4N4 + 16 HCl + S8