Sulfur is distributed in the earth's crust, among other elements it occupies the sixteenth place. It occurs both in a free state and in a bound form. Non-metallic properties are characteristic of this chemical element. Its Latin name is "Sulfur", denoted by the symbol S. The element is a part of various ions of compounds containing oxygen and / or hydrogen, forms many substances belonging to the classes of acids, salts and several oxides, each of which can be called sulfur oxide with the addition of symbols denoting valency. The oxidation states that it exhibits in various compounds are +6, +4, +2, 0, −1, −2. Sulfur oxides with varying degrees of oxidation are known. The most common are sulfur dioxide and trioxide. Less well known are sulfur monoxide, as well as higher (except SO3) and lower oxides of this element.
Sulfur monoxide
An inorganic compound called sulfur oxide II, SO, in appearance this substance is a colorless gas. Upon contact with water, it does not dissolve, but reacts with it. This is a very rare compound that occurs only in rarefied gas environments. The SO molecule is thermodynamically unstable; it is initially transformed into S2O2 (called disulfur gas or sulfur peroxide). Due to the rare occurrence of sulfur monoxide in our atmosphere and the low stability of the molecule, it is difficult to fully determine the dangers of this substance. But in a condensed or more concentrated form, the oxide turns into peroxide, which is relatively toxic and corrosive. This compound is also highly flammable (resembles methane in this property), and combustion results in sulfur dioxide, a poisonous gas. Sulfur oxide 2 was discovered near Io (one of the moons of Jupiter), in the atmosphere of Venus and in the interstellar medium. It is assumed that on Io it is obtained as a result of volcanic and photochemical processes. The main photochemical reactions are as follows: O + S2 → S + SO and SO2 → SO + O.
Sulphur dioxide
Sulfur oxide IV, or sulfur dioxide (SO2) is a colorless gas with a suffocating pungent odor. At a temperature of minus 10 C, it passes into a liquid state, and at a temperature of minus 73 C it hardens. At 20C, about 40 volumes of SO2 dissolve in 1 liter of water.
This sulfur oxide, dissolving in water, forms sulfuric acid, as it is its anhydride: SO2 + H2O ↔ H2SO3.
It interacts with bases and basic oxides: 2NaOH + SO2 → Na2SO3 + H2O and SO2 + CaO → CaSO3.
Sulfur gas is characterized by the properties of both an oxidizing agent and a reducing agent. It is oxidized by atmospheric oxygen to sulfuric anhydride in the presence of a catalyst: SO2 + O2 → 2SO3. With strong reducing agents, such as hydrogen sulfide, it plays the role of an oxidizing agent: H2S + SO2 → S + H2O.
Sulfur gas in industry is mainly used to produce sulfuric acid. Sulfur dioxide is obtained by burning sulfur or iron pyrites: 11O2 + 4FeS2 → 2Fe2O3 + 8SO2.
Sulfuric anhydride
Sulfur oxide VI, or sulfur trioxide (SO3) is an intermediate product and does not have independent significance. In appearance it is a colorless liquid. It boils at a temperature of 45 ° C, and below 17 ° C it turns into a white crystalline mass. This higher sulfur oxide (with an oxidation state of sulfur atom + 6) is extremely hygroscopic. With water, it forms sulfuric acid: SO3 + H2O ↔ H2SO4. When dissolved in water, it releases a large amount of heat and, if not a large amount of oxide is added gradually at once, then an explosion can occur. Sulfur trioxide dissolves well in concentrated sulfuric acid to form oleum. The content of SO3 in oleum reaches 60%. This sulfur compound is characterized by all the properties of acid oxide.
Higher and lower sulfur oxides
Higher sulfur oxides are a group of chemical compounds with the formula SO3 + x, where x can be 0 or 1. The monomeric SO4 oxide contains a peroxo group (OO) and is characterized, like SO3, by a sulfur oxidation state of +6. This sulfur oxide can be obtained at low temperatures (below 78 K) as a result of the reaction of SO3 and atomic oxygen or the photolysis of SO3 in a mixture with ozone.
Lower sulfur oxides are a group of chemical compounds that includes:
- SO (sulfur oxide and its dimer S2O2);
- S2O;
- sulfur monoxides SnO (are cyclic compounds consisting of rings formed by sulfur atoms, while n may be from 5 to 10);
- S7O2;
- polymer sulfur oxides.
Interest in lower sulfur oxides has increased. This is due to the need to study their contents in terrestrial and extraterrestrial atmospheres.