Sulfur Properties and Compounds
Known to the ancients (in Genesis it is called brimstone), sulfur was first classified as an element in 1777 by Antoine Lavoisier. It is estimated to be the ninth most abundant element in the universe. In the form of sulfides, sulfates, and elemental sulfur, the element constitutes about 0.03 percent of the Earth's crust. After oxygen and silicon, it is the most abundant constituent of minerals.
Occurrence, properties, and uses. Native or free sulfur occurs chiefly in volcanic or sedimentary deposits. The former are located throughout the world; the latter are especially common along the U.S. coastal region of Texas and Louisiana. Coal, petroleum, and natural gas contain sulfur compounds. Sulfur-containing ores include such sulfides as pyrite (iron disulfide), galena (lead sulfide), cinnabar (mercury sulfide), sphalerite (zinc sulfide), and chalcopyrite (copper iron sulfide), as well as such sulfates as gypsum (calcium sulfate) and barite or heavy spar (barium sulfate).
Where deposits of sulfur are located in salt domes, as they are along the coast of the Gulf of Mexico, the element is recovered by the Frasch process (q.v.). This process has made sulfur of a
About 4,000,000 tons of sulphur are recovered in the United States each year from natural gas, petroleum refinery gases, pyrites, and smelter gases from the processing of copper, zinc, and lead ores. In most cases sulfur is separated from other gases as hydrogen sulfide and then converted to elemental sulfur by the Claus process, which involves the partial burning of hydrogen sulfide to sulfur dioxide, with subsequent reaction between the two to yield sulfur. Another important source is the sulfur dioxide emitted into the atmosphere by coal-fired steam power plants. In the early 1970s techniques to collect this sulfur dioxide and convert it into usable sulfur were developed.
Pure sulfur is a tasteless, odourless, brittle solid that is pale yellow in colour, a poor conductor of electricity, and insoluble in water. The element exists in several different forms, the two most important being the orthorhombic (often called rhombic) and monoclinic crystalline modifications. Rhombic sulfur, which is stable at room temperature, includes the common roll sulfur (or brimstone) flowers of sulfur (a finely divided form obtained by sublimation of vapour directly to a solid upon cooling), and much natural sulfur. Monoclinic, or prismatic, sulfur, which is obtained when liquid sulfur is cooled slowly, consists of long, needlelike crystals. It is stable between 96 C (205 F) and 119 C (246 F), but at room temperature it changes slowly to the rhombic form. When hot molten sulfur is cooled suddenly (as by pouring it into cold water), it forms a soft, sticky, elastic,
Sulfur forms compounds in oxidation states -2 (sulfide, S2-), +4 (sulfite, SO32-), and +6 (sulfate, SO42-). It combines with nearly all elements. An unusual feature of some sulfur compounds re-sults from the fact that sulfur is second only to carbon in exhibiting catenation--i.e., the bonding of an atom to another identical atom. This allows sulfur atoms to form ring systems and chain structures. The more significant sulfur compounds and compound groups are as follows.
All the metals except gold and platinum combine with sulfur to form inorganic sulfides. Such sulfides are ionic compounds containing the negatively charged sulfide ion S2-; these compounds may be considered as salts of hydrogen sulfide. Some inorganic sulfides are important ores of such metals as iron, nickel, copper, cobalt, zinc, and lead.
Several oxides are formed by sulfur and oxygen; the most important is the heavy, colourless, poisonous gas sulfur dioxide, SO2. It is used primarily as a precursor of sulfur trioxide, or
Sulfur forms a wide variety of compounds with halogen elements. In combination with chlorine it yields sulfur chlorides such as disulfur dichloride, S2Cl2, a corrosive, golden-yellow liquid used in the manufacture of chemical products. It reacts with ethylene to produce mustard gas, and with unsaturated acids derived from fats it forms oily products that are basic components of lubricants. With fluorine, sulfur forms sulfur fluorides, the most useful of which is sulfur hexafluoride, SF6, a gas employed as an insulator in various electrical devices. Sulfur also forms oxyhalides, in which the sulfur atom is bonded to both oxygen and halogen atoms. When such compounds are named, the term thionyl is used to designate those containing the SO unit and the term sulfuryl for those with SO2. Thionyl chloride, SOCl2, is a dense, toxic, volatile liquid used in organic chemistry to convert carboxylic acids and alcohols into chlorine-containing compounds. Sulfuryl chloride, SO2Cl2, is a
Sulfur forms some 16 oxygen-bearing acids. Only four or five of them, however, have been prepared in the pure state. These acids, particularly sulfurous acid and sulfuric acid, are of
The organic compounds of sulfur constitute a diverse and important subdivision of organic substances. Some examples include the sulfur-containing amino acids (e.g., cysteine, methionine, and taurine), which are key components of hormones, enzymes, and coenzymes. Significant, too, are the synthetic organic sulfur compounds, among them numerous pharmaceuticals (sulfa drugs, dermatological agents), insecticides, solvents, and agents such as those used in preparing rubber and rayon.
Atomic number: 16
Atomic weight: 32.064
Boiling point: 444.6° C (832° F)
Density @ 20° C [68° F]
Oxidation states: -2, +4, +6
Electron configuration: 2-8-6 or 1s22s22p63s23p4