Page 217 - Academic Press Encyclopedia of Physical Science and Technology 3rd InOrganic Chemistry

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Encyclopedia of Physical Science and Technology EN009F-398 July 6, 2001 20:34

26 Main Group Elements

The cytotoxic nature of superoxide is not completely itscompounds,withgaseousFOOFallowingtransportand
understood, but one explanation suggests that the super- collection of the product. The yields are not quantitative in
oxide ion, or possibly the hydroxyl radical (·OH) produced many cases, however, and this oxidant may be displaced
in a side reaction, can function as an oxidant of certain cel- by the even more exotic KrF 2 .
lular materials, particularly the unsaturated fatty acids of
membrane lipids. Other evidence indicates a strong link
−
betweenthevariousoxygenradicals(O ,·OH,·OOH)and XI. SULFUR
2
carcinogenesis, but the significance of the relative rates of
−
formationanddestructionofO intumorcellsremainsob- Sulfur (atomic number 16) ranks sixteenth in order of
2
scure. Further investigations to ascertain the relationship abundance among the elements. Its total contribution—
between O concentrations and SOD activity in tumor- both free and combined—to crustal rock is 340 ppm; this
−
2
ous tissue may provide the information needed to develop is only about one-third the value listed for phosphorus
novel approaches to preventing and treating certain types (1120 ppm), but it is nearly twice the value for carbon
of cancer. (180 ppm).
Sulfur occurs free in many volcanic regions of the world
and in extensive underground deposits in Louisiana and
D. Hydrogen Peroxide
Texas. Although these American deposits lie buried under
Hydrogen peroxide is used industrially to bleach wood nearly 200–300 m of clay, sand, and gravel, their recovery
pulp, textiles, straw, and leather. It is also used extensively by means of the Frasch process dates from the turn of the
in pollution control efforts. It is a valuable reagent in the century. In the combined state, sulfur is found as metal
syntheses of both organic chemicals (epoxides, peroxy sulfides, as metal sulfates, and as H 2 S and organosulfur
compounds, and oxides) and inorganic chemicals (perbo- compounds in petroleum and coal. Some of the important
ratesandpercarbondates).Familiardomesticusesofdilute sulfide ores (which also serve as a source of the metal)
3% solutions of hydrogen peroxide include its application include galena (PbS), molybdenite (MoS 2 ), pyrite (FeS 2 ),
as a hair bleach and as a mild disinfectant. The efficacy sphalerite (ZnS), and cinnabar (HgS). The most important
of H 2 O 2 as an antiseptic and bacteriocide is, however, sulfates are those of the Group 2 (IIA) metals and include
somewhat dubious; consequently, the household use of epsomite (MgSO 4 · 7H 2 O), gypsum (CaSO 4 · 2H 2 O), ce-
peroxide has declined in recent years. lestite (SrSO 4 ), and barite (BaSO 4 ).
The most important future application of H 2 O 2 may be Sulfur for commercial purposes is derived mainly from
its use in agriculture. Recent studies have shown that di- elemental sulfur mined by the Frasch process or from
lute alkaline treatment of wheat straw, corncobs, and corn- the sulfur by-products of purified “sour” natural gas and
stalks can render these poorly digestible crop residues far petroleum. (The term sour is generally associated with
more nutritious to sheep and other ruminants. In one study, high-sulfur petroleum products.) During World War II,
sheep fed treated straw gained 235 g/day, about the same sulfur was first produced commercially from sour natural
gain they would realize if fed shell corn; however, sheep gas; by the early 1970s, sulfur from sour natural gas and
organosulfur compounds in crude oil already exceeded
fed only untreated straw lost 106 g/day. If alkaline H 2 O 2
treatment of fibrous agricultural waste products becomes that produced by mining elemental sulfur.
feasible, then an inexpensive, almost-unlimited food Often found in forbidding, Hades-like regions of vol-
source will be made available for livestock production. canic activity, elemental sulfur was known to prehistoric
peoples, and over the millennia a certain mystique has
been associated with it. Probably no other element, with
E. High-Energy Oxidizers
the exception of gold (“the lust for gold,”“the golden
Space technology has led to extensive research into the touch,”“the glint of gold,”“the golden fleece”) has en-
synthesis and properties of high-energy oxidizers for po- joyed this mystical aura. The fact that rock sulfur burned
tential use in rocket engines. Among the products of such was obviously impressive to the ancients, but the horri-
research is dioxygen difluoride, FOOF. The compound is ble choking fumes of the sulfur dioxide produced must
have been equally impressive. Sulfur was called brimstone
prepared by passing a low-pressure mixture of F 2 and O 2
through a silent discharge. A very unstable compound, (brennstein, “the stone that burns”), and it was frequently
it decomposes at a rate of ∼4%/day at −160 C. A po- associated with Stygian origins and infernal punishments.
◦
tentially important use of this powerful oxidant has been In later centuries, sulfur was central to the efforts of al-
developed at the Los Alamos Scientific Laboratory for chemists, who vainly labored to transmute lead to gold by
recovery of waste and scrap plutonium. Volatile PuF 6 is transferring the yellow color of sulfur into the base metal.
produced on contact of a variety of forms of the metal and Sulfur was also associated with the phlogiston theory of