Carbon tetraiodide is CI4, a tetrahalomethane. Being bright red, it is a relatively rare example of a highly colored methane derivative. It is only 2% by weight carbon, although other methane derivatives are known with still less carbon. The tetrahedral molecule features C-I distances of 2.12 ± 0.02 Å. The molecule is slightly crowded with short I---I contacts of 3.459 ± 0.03 Å, and possibly for this reason, it is thermally and photochemically unstable. Hexaiodoethane is unknown, probably for the same reason.
Properties, synthesis, uses
CI4 is slightly reactive towards water, giving iodoform and I2. Otherwise it is soluble in nonpolar organic solvents. It decomposes thermally and photochemically to tetraiodoethylene, I2C=CI2. Its synthesis entails AlCl3-catalyzed halide exchange, which is conducted at room temperature:
CCl4 + 4 EtI ? CI4 + 4 EtCl
The product crystallizes from the reaction solution.
CI4 is used as an iodination reagent, often upon reaction with base. Ketones are converted to 1,1-diiodoethenes upon treatment with PPh3 and CI4. Alcohols are converted in and to iodide, by a mechanism similar to the Appel reaction. In an Appel reaction carbon tetrachloride is used to generate the chloride from alcohols.
Safety considerations
Manufacturers recommend that CI4 be stored near 0 °C. As a ready source of iodine, it is an irritant. LD50: 178 mg kg–1. In general perhalogenated organic compounds should be considered toxic.
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Rabu, 11 Februari 2009
Calcium fluoride
Calcium fluoride (CaF2) is an insoluble ionic compound of calcium and fluorine. It occurs naturally as the mineral fluorite (also called fluorspar), and it is the source of most of the world's fluorine. It reacts with concentrated sulfuric acid to produce hydrogen fluoride:
CaF2(s) + H2SO4(l) ? CaSO4(s) + 2 HF(g) This is the reaction used to produce hydrogen fluoride in industry.
Applications
Calcium fluoride is commonly used as a window material for both infrared and ultraviolet wavelengths, since it is transparent in these regions (about 0.15 µm to 9 µm) and exhibits extremely weak birefringence. Nevertheless, at wavelengths as low as 157 nm, which are interesting to semiconductor manufacturers, the birefringence of calcium fluoride exceeds tolerable limits. This may be overcome by minimizing birefringence by optimimizing the growth process. It is particularly important as an ultraviolet optical material for integrated circuit lithography. Canon also uses artificially-crystallized calcium fluoride elements in some of its L-series lenses to reduce light dispersion. As an infrared optical material, calcium fluoride is sometimes known by the Eastman Kodak trademarked name Irtran-3, although this designation is long since obsolete.
Uranium-doped calcium fluoride was the second type of solid state laser invented, in the 1960s. Peter Sorokin and Mirek Stevenson at IBM's laboratories in Yorktown Heights, New York, achieved lasing at 2.5 µm shortly after Maiman's ruby laser.
CaF2(s) + H2SO4(l) ? CaSO4(s) + 2 HF(g) This is the reaction used to produce hydrogen fluoride in industry.
Applications
Calcium fluoride is commonly used as a window material for both infrared and ultraviolet wavelengths, since it is transparent in these regions (about 0.15 µm to 9 µm) and exhibits extremely weak birefringence. Nevertheless, at wavelengths as low as 157 nm, which are interesting to semiconductor manufacturers, the birefringence of calcium fluoride exceeds tolerable limits. This may be overcome by minimizing birefringence by optimimizing the growth process. It is particularly important as an ultraviolet optical material for integrated circuit lithography. Canon also uses artificially-crystallized calcium fluoride elements in some of its L-series lenses to reduce light dispersion. As an infrared optical material, calcium fluoride is sometimes known by the Eastman Kodak trademarked name Irtran-3, although this designation is long since obsolete.
Uranium-doped calcium fluoride was the second type of solid state laser invented, in the 1960s. Peter Sorokin and Mirek Stevenson at IBM's laboratories in Yorktown Heights, New York, achieved lasing at 2.5 µm shortly after Maiman's ruby laser.
Bromine
Bromine (Greek: brómos, meaning "stench (of he-goats)"), is a chemical element in the periodic table that has the symbol Br and atomic number 35. A halogen element, bromine is a red volatile liquid at standard room temperature which has a reactivity between chlorine and iodine. This element is corrosive to human tissue in a liquid state and its vapors irritate eyes and throat. Bromine vapors are very toxic upon inhalation.
Notable characteristics
Bromine is the only liquid nonmetallic element at room temperature and one of five elements on the period table that are liquid at or close to room temperature. The pure chemical element has the physical form of a diatomic molecule, Br2. It is a heavy, mobile, reddish-brown liquid, that evaporates easily at standard temperature and pressures in a red vapor (its color resembles nitrogen dioxide) that has a strong disagreeable odor resembling that of chlorine. A halogen, bromine resembles chlorine chemically but is less active. It is more active than iodine, however. Bromine is slightly soluble in water, and highly soluble in carbon disulfide, aliphatic alcohols (such as methanol), and acetic acid. It bonds easily with many elements and has a strong bleaching action.
Bromine is highly reactive and is a powerful oxidizing agent in the presence of water. It reacts vigorously with amines, alkenes and phenols as well as aliphatic and aromatic hydrocarbons, ketones and acids (these are brominated by either addition or substitution reactions). With many of the metals and elements, anhydrous bromine is less reactive than hydrated bromine; however, dry bromine reacts vigorously with aluminum, titanium, mercury as well as alkaline earth metals and alkaline metals.
Due to its contribution to ozone depletion in Earth's atmosphere, bromine has been evaluated to have an ozone depletion potential of 60 when compared to chlorine.
Applications
Elemental bromine is used to manufacture a wide variety of bromine compounds used in industry and agriculture. Traditionally the largest use of bromine was in the production of 1,2-dibromoethane which in turn was used as a gasoline anti-knock agent for leaded gasoline before they were largely phased out due to environmental considerations.
Bromine is also used in the manufacture of fumigants, brominated flame-retardants, water purification compounds, dyes, medicines, sanitizers, inorganic bromides for photography, etc. It is also used to form intermediates in organic synthesis, where it is preferred to iodine due to its much lower cost.
Bromine is used to make brominated vegetable oil, which is used as an emulsifier in many citrus-flavored soft drinks.
Aqueous bromine is orange and can be used in tests for alkenes and phenols.
• When added to an alkene it will lose its color as it reacts forming a colorless bromoalkane. For example, reaction with ethylene will produce 1,2-dibromoethane.
• When added to phenol a white precipitate, 2,4,6-tribromophenol, will form. With aniline, 2,4,6 tribromoaniline will precipitate (even in water)
History
Bromine was discovered by Antoine Balard at the salt marshes of Montpellier in 1826 but was not produced in quantity until 1860. The French chemist and physicist Joseph-Louis Gay-Lussac suggested the name bromine due to the characteristic smell of the vapors.
Occurrence
Bromine occurs in nature as bromide salts in very diffuse amounts in crystal rock. Due to leaching, bromide salts have accumulated in sea water (85 ppm), and may be economically recovered from brine wells and the Dead Sea (up to 5000 ppm).
Approximately 500 million kilograms ($350 million USD) of bromine are produced per year (2001) worldwide with the United States and Israel being the primary producers. The largest bromine reserve in the United States is located in Columbia and Union County, Arkansas.
Safety
Elemental bromine is a strong irritant and, in concentrated form, will produce painful blisters on exposed skin and especially mucous membranes. Even low concentrations of bromine vapor (from 10 ppm) can affect breathing, and inhalation of significant amounts of bromine can seriously damage the respiratory system.
Notable characteristics
Bromine is the only liquid nonmetallic element at room temperature and one of five elements on the period table that are liquid at or close to room temperature. The pure chemical element has the physical form of a diatomic molecule, Br2. It is a heavy, mobile, reddish-brown liquid, that evaporates easily at standard temperature and pressures in a red vapor (its color resembles nitrogen dioxide) that has a strong disagreeable odor resembling that of chlorine. A halogen, bromine resembles chlorine chemically but is less active. It is more active than iodine, however. Bromine is slightly soluble in water, and highly soluble in carbon disulfide, aliphatic alcohols (such as methanol), and acetic acid. It bonds easily with many elements and has a strong bleaching action.
Bromine is highly reactive and is a powerful oxidizing agent in the presence of water. It reacts vigorously with amines, alkenes and phenols as well as aliphatic and aromatic hydrocarbons, ketones and acids (these are brominated by either addition or substitution reactions). With many of the metals and elements, anhydrous bromine is less reactive than hydrated bromine; however, dry bromine reacts vigorously with aluminum, titanium, mercury as well as alkaline earth metals and alkaline metals.
Due to its contribution to ozone depletion in Earth's atmosphere, bromine has been evaluated to have an ozone depletion potential of 60 when compared to chlorine.
Applications
Elemental bromine is used to manufacture a wide variety of bromine compounds used in industry and agriculture. Traditionally the largest use of bromine was in the production of 1,2-dibromoethane which in turn was used as a gasoline anti-knock agent for leaded gasoline before they were largely phased out due to environmental considerations.
Bromine is also used in the manufacture of fumigants, brominated flame-retardants, water purification compounds, dyes, medicines, sanitizers, inorganic bromides for photography, etc. It is also used to form intermediates in organic synthesis, where it is preferred to iodine due to its much lower cost.
Bromine is used to make brominated vegetable oil, which is used as an emulsifier in many citrus-flavored soft drinks.
Aqueous bromine is orange and can be used in tests for alkenes and phenols.
• When added to an alkene it will lose its color as it reacts forming a colorless bromoalkane. For example, reaction with ethylene will produce 1,2-dibromoethane.
• When added to phenol a white precipitate, 2,4,6-tribromophenol, will form. With aniline, 2,4,6 tribromoaniline will precipitate (even in water)
History
Bromine was discovered by Antoine Balard at the salt marshes of Montpellier in 1826 but was not produced in quantity until 1860. The French chemist and physicist Joseph-Louis Gay-Lussac suggested the name bromine due to the characteristic smell of the vapors.
Occurrence
Bromine occurs in nature as bromide salts in very diffuse amounts in crystal rock. Due to leaching, bromide salts have accumulated in sea water (85 ppm), and may be economically recovered from brine wells and the Dead Sea (up to 5000 ppm).
Approximately 500 million kilograms ($350 million USD) of bromine are produced per year (2001) worldwide with the United States and Israel being the primary producers. The largest bromine reserve in the United States is located in Columbia and Union County, Arkansas.
Safety
Elemental bromine is a strong irritant and, in concentrated form, will produce painful blisters on exposed skin and especially mucous membranes. Even low concentrations of bromine vapor (from 10 ppm) can affect breathing, and inhalation of significant amounts of bromine can seriously damage the respiratory system.
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