Nitrogen Sulphide, N₄S₄

Nitrogen sulphide may be prepared by the action of dry ammonia on "sulphur dichloride" dissolved in either carbon disulphide or benzene:

6SCl₂ + 16NH₃ = N₄S₄ + 2S + 12NH₄Cl.

The ammonium chloride separates out in flakes, the solution becoming orange-red in colour. Since it is less soluble in carbon disulphide than sulphur, the nitrogen sulphide may be extracted from the product by fractional crystallisation from that solvent.

When ammonia and sulphur monochloride, S₂Cl₂, each in ice-cold chloroform solution, are mixed, the main course of the reaction is:

6S₂Cl₂ + 16NH₃ = N₄S₄ + 8S + 12NH₄Cl.

After the sulphide N₄S₄ has been precipitated by the addition of alcohol, the mother-liquor on concentration yields nitrogen pentasulphide, N₂S₅, and also hexasulphamide, S₆NH₂.

Sulphur reacts with liquid ammonia according to the equation:

10S + 4NH₃ = N₄S₄ + 6H₂S.

The hydrogen sulphide may be removed as silver sulphide, whilst the nitrogen sulphide in the filtrate can be isolated by extraction with carbon disulphide.

Nitrogen sulphide forms orange-coloured translucent monoclinic crystals with flat lustrous surfaces, a:b:c = 0.8806:1:0.8430; β = 89°20'. It has a density of 2.2, and melts at 179° C., but the melting-point is considerably lowered by the presence of free sulphur. Sublimation occurs near the melting-point, and as the temperature rises the substance becomes highly explosive. It also detonates violently when struck. When heated in a vacuum, nitrogen sulphide sublimes without decomposition, but when sublimed in a vacuum over silver gauze at 360° C., the sulphide is decomposed, the sulphur combining with the silver. Burt noticed that, in addition to the evolution of nitrogen and the formation of silver sulphide due to the action of the silver gauze, a blue sulphide was also obtained having the same empirical formula as the yellow sulphide, thus furnishing an example of inorganic polymerism.

Nitrogen sulphide is only sparingly soluble in alcohol, ether, wood spirit and turpentine; it is hydrolysed by water or moist air with formation of ammonium thiosulphate, ammonium trithionate and ammonia:

2N₄S₄ + 15H₂O = (NH₄)₂S₂O₃ + 2(NH₄)₂S₃O₆ + 2NH₃.

With hot water the reaction is violent.

With the alkalis the corresponding sulphite, thiosulphate and ammonia are formed:

N₄S₄ + 6KOH + 8H₂O = 2K₂SO₃ + K₂S₂O₃ + 4NH₃.

Dry ammonia has no action, but the sulphide dissolves in liquid anhydrous ammonia at -40° C., yielding a red solution. After evaporation of the ammonia an orange or brown powder remains containing up to two molecules of ammonia, but this powder dissociates slowly even at ordinary temperatures.

Solutions of metallic iodides in anhydrous ammonia form precipitates with nitrogen sulphide in ammoniacal solution. Lead iodide thus forms the compound lead dithiodi-imide, PbN₂S₂.NH₃, which crystallises in olive-green prisms, turning orange on exposure to the air. Hydrochloric acid reacts quantitatively with this lead compound according to the equation:

PbN₂S₂.NH₃ + 6HCl = PbCl₂ + 3NH₃ + 2S + 2Cl₂.

Dry liquid hydrogen sulphide reacts in accordance with the equation:

PbN₂S₂.NH₃ + 3H₂S = PbS + 4S + 3NH₃.

Although prepared in a similar manner to the lead compound, the product formed with mercury iodide contains one atom less of sulphur per molecule, thus, mercury thiodi-imide, HgN₂S.NH₃.

Ruff and Geisel assume that the compound of nitrogen sulphide with ammonia dissociates in anhydrous ammonia solution forming (a), , and (6), S:S(NH)₂, of which the former yields an insoluble mercuric salt, , and the latter an insoluble lead salt, . Vosnessenski formulates the mercury salt as .

Under similar conditions the cyanides of potassium, magnesium and aluminium form the corresponding thiocyanates. There are indications that the sulphur nitride reacts with ammonium sulphide in the solution to give sulphur, which then interacts with the cyanide:

N₄S₄ + 6(NH₄)₂S = 16NH₃ + 10S.

Silver and mercuric cyanides form thiocyanates, but considerable amounts of sulphides are also precipitated.

Heated to 120° C. in a closed platinum vessel, hydrogen fluoride and nitrogen sulphide unite to form a red liquid, which readily decomposes into its constituents. In the presence of traces of moisture, thionyl fluoride is formed. Dry hydrogen chloride reacts with nitrogen sulphide according to the equation:

N₄S₄ + 12HCl = 4NH₃ + 4S + 6Cl₂.

The sulphide, dissolved in benzene or alcohol, reacts with hydrogen sulphide forming ammonium polysulphide or ammonium thiosulphate, respectively.

Many salts are capable of forming additive products with nitrogen sulphide, the components interacting in carbon tetrachloride solution. With titanium tetrachloride, TiCl₂, a brownish-red amorphous compound is formed which reacts vigorously with water and with alkalis. According to Wolbling this substance has the composition N₄S₄.TiCl₂, but according to Davis the composition is N₄S₄.Ti₂Cl₆, reduction having taken place. Antimony pentachloride gives a stable scarlet compound, N₄S₄.SbCl₅. Stannic chloride yields an analogous red compound, 2N₄S₄.SnCl₂. Stannous chloride does not combine directly with nitrogen sulphide, but in warm benzene solution a yellow compound is obtained, the constitution of which has not been determined. With selenium dichloride a green compound, N₄S₄.SeCl₂, is obtained. In the case of tungsten hexachloride the compound formed is N₄S₄.WCl₂, reduction having taken place.

The addition of "sulphur dichloride" to nitrogen sulphide in solution also yields additive products, the following having been prepared: 3N₄S₄.2SCl₂, N₄S₄.SCl₂ and N₄S₄.2SCl₂.

Nitrogen sulphide acts slowly on the acids of the paraffin series. In the case of acetic acid there is an evolution of sulphur dioxide, and sulphur and ammonium sulphate are obtained, as well as small quantities of free nitrogen. Considerable quantities of acetamide and diacetamide are also formed. The sulphide is indifferent towards primary and secondary bases of the aromatic series and towards all tertiary bases. Nitrogen sulphide has been claimed to assist the vulcanisation of rubber.

According to Schenck, and Clever and Muthmann, nitrogen sulphide has the constitution

.

Ruff and Geisel consider that its most probable constitution is

,

their researches on the sulphur halides rendering the bivalency of all the sulphur atoms in the sulphide improbable.

The latter formula is in accordance with the behaviour of the sulphide on hydrolysis, its reaction with hydrogen chloride, and with the formulation of the metallic derivatives and . The action of acetyl chloride, which produces the compound N₃S₄Cl, and the recovery of nitrogen sulphide from this compound by the action of ammonia, are facts which cannot be explained by this formula.