Sulfur
Sulfur occurs naturally as the pure element (native sulfur) and as sulfide and sulfate minerals. Elemental sulfur crystals are commonly sought after by mineral collectors for their distinct, brightly colored polyhedron shapes. Being abundant in native form, sulfur was known in ancient times, mentioned for its uses in ancient India, ancient Greece, China and Egypt. Fumes from burning sulfur were used as fumigants, and sulfur-containing medicinal mixtures were used as balms and antiparasitics. Sulfur is referenced in the Bible as brimstone (burn stone) in English, with this name still used in several nonscientific tomes. It was needed to make the best quality of black gunpowder. In 1777, Antoine Lavoisier helped convince the scientific community that sulfur was a basic element, rather than a compound.
Elemental sulfur was once extracted from salt domes where it sometimes occurs in nearly pure form, but this method has been obsolete since the late 20th century. Today, almost all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants from natural gas and petroleum. The element's commercial uses are primarily in fertilizers, because of the relatively high requirement of plants for it, and in the manufacture of sulfuric acid, a primary industrial chemical. Other well-known uses for the element are in matches, insecticides and fungicides. Many sulfur compounds are odoriferous, and the smell of odorized natural gas, skunk scent, grapefruit, and garlic is due to sulfur compounds. Hydrogen sulfide produced by living organisms imparts the characteristic odor to rotting eggs and other biological processes.
Sulfur is an essential element for all life, and is widely used in biochemical processes. In metabolic reactions, sulfur compounds serve as both fuels and respiratory (oxygen-alternative) materials for simple organisms. Sulfur in organic form is present in the vitamins biotin and thiamine, the latter being named for the Greek word for sulfur. Sulfur is an important part of many enzymes and in antioxidant molecules like glutathione and thioredoxin. Organically bonded sulfur is a component of all proteins, as the amino acids cysteine and methionine. Disulfide bonds are largely responsible for the mechanical strength and insolubility of the protein keratin, found in outer skin, hair, and feathers, and the element contributes to their pungent odor when burned.
Natural occurrence
32S is created inside massive stars, at a depth where the temperature exceeds 2.5×109 K, by the fusion of one nucleus of silicon plus one nucleus of helium. As this is part of the alpha process that produces elements in abundance, sulfur is the 10th most common element in the universe.
Sulfur, usually as sulfide, is present in many types of meteorites. Ordinary chondrites contain on average 2.1% sulfur, and carbonaceous chondrites may contain as much as 6.6%. It is normally present as troilite (FeS), but there are exceptions, with carbonaceous chondrites containing free sulfur, sulfates and other sulfur compounds. The distinctive colors of Jupiter's volcanic moon Io are attributed to various forms of molten, solid and gaseous sulfur.
On Earth, elemental sulfur can be found near hot springs and volcanic regions in many parts of the world, especially along the Pacific Ring of Fire; such volcanic deposits are currently mined in Indonesia, Chile, and Japan. Such deposits are polycrystalline, with the largest documented single crystal measuring 22×16×11 cm. Historically, Sicily was a large source of sulfur in the Industrial Revolution.
Significant deposits of elemental sulfur, believed to have been (and are still being) synthesised by anaerobic bacteria on sulfate minerals like gypsum, exist in salt domes along the coast of the Gulf of Mexico, and in evaporites in eastern Europe and western Asia. Native sulfur may be produced by geological processes alone. Fossil-based sulfur deposits from salt domes have until recently been the basis for commercial production in the United States, Russia, Turkmenistan, and Ukraine. Currently, commercial production is still carried out in the Osiek mine in Poland. Such sources are now of secondary commercial importance, and most are no longer worked.
Common naturally occurring sulfur compounds include the sulfide minerals, such as pyrite (iron sulfide), cinnabar (mercury sulfide), galena (lead sulfide), sphalerite (zinc sulfide) and stibnite (antimony sulfide); and the sulfates, such as gypsum (calcium sulfate), alunite (potassium aluminium sulfate), and barite (barium sulfate). On Earth, just as upon Jupiter's moon Io, elemental sulfur occurs naturally in volcanic emissions, including emissions from hydrothermal vents.
| Symbol | S | |
| Atomic Number | 16 | |
| Atomic Weight | 32.068 | |
| Oxidation States | +4,+6,-2 | |
| Electronegativity, Pauling | 2.58 | |
| State at RT | Solid, Nonmetal | |
| Melting Point, K | 386 | |
| Boiling Point, K | 717.824 |
Interesting Facts about Sulfur
- Sulfur makes up almost 3% of the earth’s mass. If you think that’s not much, next time you look to the sky and see the moon, think of this: the earth contains enough sulfur to make not just one new moon, but two!
- When Shakespeare’s Othello asks for punishment, one possibility he mentions is: “…roast me in sulphur!”
- Sulfur burns with a very satisfying blue flame – its old name is brimstone, which means ‘burn stone’ or ‘stone that burns.’
- Pure sulfur has no smell, but many of its compounds stink! For example sulfur compounds called mercaptans give skunks their awful smell. Rotten eggs (and most stink bombs) get their distinctive aroma courtesy of hydrogen sulfide, H2S.
- Cave bacteria, which digest hydrogen sulfide, produce snottites (think of slimy stalactites) in caves. These snottites drip sulfuric acid with a pH as low as zero – that’s enough to burn holes in your clothes if you stand underneath them. Snottite bacteria thrive in areas where there are sulfur deposits or sulfur-containing minerals or hydrocarbons. The sulfuric acid they excrete carves out new cave systems underground by dissolving rocks.
- There’s a much higher proportion of sulfur in the earth’s core than in its crust – approximately 100 times more.
Appearance and Characteristics
Harmful effects:
Elemental sulfur is considered to be of low toxicity.
Compounds such as carbon disulfide, hydrogen sulfide, and sulfur dioxide are toxic. For example, at 0.03 parts per million, we can smell hydrogen sulfide but it is regarded as safe for eight hours of exposure. At 4 ppm it may cause eye irritation. At 20 ppm exposure for more than a minute causes severe injury to eye nerves. At 700 ppm breathing stops. Death will result if there is not a quick rescue. Permanent brain damage may result.
Characteristics:
- Sulfur is a soft, pale yellow, odorless, brittle solid. It is insoluble in water, but soluble in carbon disulfide. It burns with a blue flame, oxidizing to sulfur dioxide.
- Sulfur exists in several crystalline and amorphous allotropes. The most common form is yellow, orthorhombic alpha-sulfur, which contains puckered rings of S8.
- Sulfur is multivalent and combines, with valence 2, 4, or 6, with almost all other elements. The best known sulfur compound is hydrogen sulfide (H2S). This is a toxic gas that smells like rotten eggs; the smell is used in stink bombs, many of which release a small amount of hydrogen sulfide.
Uses of Sulfur
- Sulfur’s main commercial use is as a reactant in the production of sulfuric acid (H2SO4). Sulfuric acid is the industrialized world’s number one bulk chemical, required in large quantities in lead-acid batteries for automotive use.
- Sulfur is also used in the vulcanization of natural rubber, as a fungicide, in black gunpowder, in detergents and in the manufacture of phosphate fertilizers.
- Sulfur is a vital element for all forms of life. It is a component of two amino acids, cysteine and methionine.
- Penicilin is a natural, sulfur-based antibiotic.
Sulfur reacts very vigorously with zinc. Here’s a test firing of a sulfur/zinc rocket.
Crystallization of liquid sulfur.
