| Organosulfur Compounds |
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Sulfur shares the Chalcogen group with oxygen and it is expected that organosulfur compounds have similarities with compounds of carbon and oxygen. THIOETHERS AND THIOPHENES The carbon to sulfur Bond in Thioether s is both longer and weaker than that of the carbon to carbon bond. Selected Bond Length s in sulfur compounds are 183 Pm for the S-C single bond in Methanethiol and 173 pm in Thiophene . The Bond Dissociation Energy for thiomethane is 89 Kcal/mol compared to methane's 100 Kcal/mol and when hydrogen is replaced by a methyl group the energy decreases to 73 Kcal/mol. The single carbon to oxygen bond is shorter than that of the C-C bond. The Bond Dissociation Energies for Dimethylsulfide and Dimethyl Ether are respectively 73 and 77 Kcal/mol. Thioethers can be prepared via the Pummerer Rearrangement . The Resonance Stabilization of thiophene is 29 Kcal/mol compared to 20 kcal/mole for the oxygen pendant Furan . The reason for this difference is the higher Electronegativity for oxygen drawing away electrons to itself at the expense of the aromatic ring current. Yet as an aromatic Substituent the thio group is less effective as an Activating Group than the alkoxy group. Double Bond s of carbon and sulfur exist as Sulfonium Ylide s for instance in the Johnson-Corey-Chaykovsky Reaction . THIOLS The Thiol group (R-SH) is similar to the Alcohol group but sulfur in a thiol is more Nucleophilic and a thiol is also more acidic. This acidity can differ by 5 PKa units. The diffence in Electronegativity between sulfur (2.58) and hydrogen (2.20) is small and therefore Hydrogen Bonding in thiols is not prominent. Aliphatic thiols are very effective in forming Gold Monolayer s in Nanotechnology . The related Thioacetal s represent Umpolung of carbonyl groups. SULFOXIDES, SULFONES & THIOKETONES A Sulfoxide has the general structure RS=OR and can be obtained by oxidation of Thioether s. Sulfoxides can be oxidized even further to Sulfone s (R(O=S=O)R). A Thioketone has the the general structure RC=SR and is the sulfur Carbonyl equivalent. An important route to thioketones is reaction of ketones with Lawesson's Reagent . SULFONIC ACIDS, ESTERS, AMIDES Sulfonic Acid s with general structure R(S=0)OH are strong acids and acids with solubility in organic solvents. Sulfonic acids like Trifluoromethanesulfonic Acid is a frequently used reagent in Organic Chemistry . Sulfonamide s or sulfa drugs are important Drug s derived from Aromatic Sulfonation . ORGANOSULFUR POLLUTION Some organosulfur compounds in the environment, particularly the air, are created as rare by-products of chemical plant production processes, where sulfur is used as one Reagent in a process such as making plastics or tires. But most sulfurous pollutants occur from use of Fossil Fuel s as part of a process feedstock, or when used as fuel as in power generation. Selected smell-producing processes are organosulfur compounds produced by the coking of coal designed to drive out sulfurus compounds and other volatile impurities in order to produce 'clean carbon' ( Coke ), which is primarily used for steel production. Odors occur as well in Chemical processing of Coal or Crude Oil into precursor chemicals ( Feedstocks ) for downstream industrial uses (e.g. Plastics or pharmaceutical production) and the ubiquitous needs of petroleum distillation for ( Gasoline s, Diesel , and other grades of Fuel Oils production. Organosulfur compounds might be understood as smelly contaminants that need to be removed from natural gas before commercial uses, from exhaust stacks and exhaust vents before discharge. In this latter context, organosulfur compounds may be said to account for the pollutants in sulfurous Acid Rain , or equivalently, said to be pollutants within most common fossil fuels, especially Coal . Not all organosulfur compounds are foul-smelling pollutants. Compounds like Allicin and Ajoene are responsible for the odor of Garlic , and Lenthionine contributes to the flavor of Shiitake Mushrooms . Many of these natural products also have important medicinal properties such as preventing Platelet aggregation or fighting cancer. SEE ALSO
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