Sulfides include organic and inorganic chemical compounds, the sulfur atom in their molecule is connected to metals or some non-metals. Characteristic compounds for inorganic sulfides are hydrogen sulfide (H2S), which belongs to the acid class, and ammonium sulfide (formula (NH4) 2S), which belongs to the class of salts. Also sulfides of metals and nonmetals with the general formula KxSy (where K is the cation of a metal or nonmetal, and S is the acid residue of hydrogen sulfide, x and y are the number of metal cations and anions of the acid residue in the molecule, respectively), belong to the class of salts. For example, iron (II) sulfide FeS. Organic sulfides are chemicals, the sulfur atom in their molecule is bound to hydrocarbon radicals. These are mercaptides (thioesters), their general formula is RSR ′, and R and R ′ are hydrocarbon radicals.
All chemical compounds in the molecules of which a metal atom, as well as atoms of certain non-metals (boron B, phosphorus P, silicon Si, arsenic As), are associated with a sulfur atom (S) with an oxidation state of minus 2, are usually considered salts of hydrogen sulfide acid H2S . Inorganic sulfides (except H2S), for example, ammonium sulfide or boron sulfide, should be classified as medium salts, since both hydrogen atoms in hydrogen sulfide acid are replaced by other cations. If in hydrogen sulfide acid only one atom is replaced by cations (which is typical for alkaline earth and alkali metals), then the salt formed will be an acid salt. Examples of inorganic hydrosulfides (aka bisulfides) can be compounds such as ammonium hydrosulfide (formula NH4HS) or sodium hydrosulfide (NaHS). In hydrosulfide molecules, unlike sulfides, HS- is the acid residue or anion. Organic hydrosulfides include mercaptans (thioalcohols and thiols) with the general formula RSH, where R is a hydrocarbon radical. Mercaptids and mercaptans are characterized by an extensive nomenclature, so they require additional consideration.
Most sulfides are brightly colored. In water, only ammonium sulfide and alkali metal sulfides are well soluble . Sulfides of other metals are practically insoluble in water. Since sulfides are salts of weak hydrosulphuric acid, their water-soluble representatives can undergo hydrolysis. For sulfides formed by metals with a high degree of oxidation or, if their hydroxides are weak bases (for example, Cr2S3, Al2S3 and others), more often hydrolysis proceeds irreversibly. Sulfides are mild reducing agents that react with atmospheric oxygen at elevated temperatures to form salts in which the sulfur atom has a higher oxidation state, for example, sulfates and sulfur dioxide. Ammonium sulfide is used in photography, in textile production. Sulfides are used as semiconductor materials, phosphors, in medicine, in agriculture.
Sulfides can be obtained by various methods. Ammonium sulfide (another name for this salt is also known - diammonium sulfide) is obtained by the interaction of hydrogen sulfide with an excess of ammonia: H2S + 2 NH3 → (NH4) 2S. The more stable salt of hydrogen sulfide is iron sulfide FeS, which can decompose only when heated in vacuum, it turns out (this is one of many known methods) as a result of the irreversible reaction of sulfur with iron: Fe + S → FeS.
The molecular weight of ammonium sulfide is 68.14 a. e. m. The gross formula according to the Hill system is written in the form: H8N2S. In appearance, the salt resembles colorless crystals. Ammonium sulfide at 20 ° C is well soluble in water. Soluble in ethanol. It is a hygroscopic substance that can absorb moisture. In the free state, ammonium sulfide was not obtained. Since (NH4) 2S is an unstable salt, its aqueous solutions are approximated by hydrosulfide and, thus, consist mainly of a mixture of NH3 and NH4HS, and aqueous solutions of (NH4) 2S are a colorless liquid with the smell of ammonia and hydrogen sulfide. The solution is alkaline with a pH of up to 9.3. Hard salt crystals cannot be isolated, even with strong cooling of the solution. As a result of oxidation by atmospheric oxygen and the formation of polysulfides, the ammonium sulfide solution quickly turns yellow. Therefore, the sulfide solution should be stored in a bottle filled to the very stopper, as well as tightly corked.
The molecular weight of ammonium hydrosulfide is 51.11 a. e. m. The gross formula according to the Hill system is written in the form: H5NS. Salt in appearance is a colorless crystals of rhombic shape. The density of the salt is 0.89 g / cm3. The melting point is 120 ° C (under pressure). At room temperature, evaporation and sublimation of the reagent vapor is observed. This compound is volatile at room temperature. The substance is highly soluble in ethanol and cold water, decomposes in hot water or with slight heating. The reaction of an aqueous solution of salt is alkaline. In air, ammonium hydrosulfide is able to oxidize, therefore, its solution from colorless during storage quickly turns yellow due to the formation of polysulfides. Ammonium hydrosulfide can be obtained by direct interaction of ammonia with hydrogen sulfide in diethyl (sulfur) ether or by passing at 0 ° C through an ammonia solution an excess of hydrogen sulfide according to the reaction equation: NH3 + H2S → NH4HS.