Nitrous ozone layer depletion

Nitrous oxide is produced as a byproduct in multimillion Ib/year quantities in nylon manufacture worldwide. Currently, there is a great interest toward the utilization of NjO due to the environmentally hazardous nature of this gas with respect to the greenhouse effect and ozone layer depletion. In addition to their ability to utilize dioxygen for catalytic hydrocarbon oxidations, ruthenium porphyrins have been shown to activate nitrous oxide which is an extremely inert molecule and a poor ligand. Groves and Roman have found that N O reacted with Ru"(TMP)(THF)2 in toluene to produce Ru (TMP)(0)2 . trans-dioxoRu(VI) complex can in turn epoxidize a suitable substrate such as tra/js-p-methyl styrene. This system was subsequently shown to be catalytic under appropriate conditions . 

Four billion pounds of adipic acid are produced each year using petroleum-based feedstocks, carcinogenic benzene as starting material, and extreme reaction conditions. Nitrous oxide, which plays a role in ozone layer depletion, is emitted as a byproduct. As an alternative to the currently employed synthetic methcdology, a two-step synthesis of adipic acid from D-glucose has been developed which eliminates each of these problems. A microbial catalyst was created which possesses a novel biosynthetic pathway that synthesizes cis, cis-muconic acid from D-glucose. This pathway does not occur in nature but has been created in a strain of Escherichia colL Cis, cw-muconic acid is exported to the culture supernatant, where it is hydrogenated under mild conditions to yield adipic acid. 

Adipic acid is a six-carbon diacid used primarily in production of nylon-6,6. The annual global demand for adipic acid is in the range of 2 billion kilograms, and it is perennially among the top 50 chemicals produced in the U.S. each year. Adipic acid is manufactured from benzene, where the final step of the reaction sequence requires nitric acid oxidation of cyclohexanone and cyclohexanol. Nitrous oxide, a byproduct of the oxidation, has been implicated in ozone layer depletion and the greenhouse effect. Adipic acid production has been estimated to account for approximately 10% of the annual increase in atmospheric nitrous oxide levels (25). 

Since nitrous oxide, NjO, is a designated "greenhouse" gas, and may contribute to depletion of the ozone layer, its removal from emissions to atmosphere is desirable [1]. However, there are several reports that NjO can be formed at low selectivity as an undesirable by-product of NO+CO conversions during the initial warm-up-from-cold periods in three-way-catalytic (TWC) converters or components thereof [1-3]. TWC s commonly contain Rhodium and Ceria and although N,0 dissociation over RhjO, has been extensively studied [4], the following are among mechanistic possibilities as yet... 

A compressed gas used to expel the contents of containers in the form of aerosols. Chlorofluorocarbons were once widely used because of their nonflammability. The strong possibility that they contribute to depletion of the ozone layer of the upper atmosphere has resulted in prohibition of their use for this purpose. Other propellants used are hydrocarbon gases, such as butane and propane, carbon dioxide, and nitrous oxide. The materials dispersed include insecticides, shaving cream, whipping cream,andcosmeticpreparations. See ozone (note). 

A by-product of this oxidation is nitrous oxide, a gas considered to play a role in global warming and the depletion of the ozone layer in the atmosphere, as well as contributing to acid rain and acid smog. Given the fact that worldwide production of adipic acid is approximately 2.2 billion metric tons per year, the production of nitrous oxide is enormous. In spite of technological advances that allow for the recovery and recycling of nitrous oxide, it is estimated that approximately 400,000 metric tons escapes recovery and is released into the atmosphere each year. 

Nitrous oxide and chlorinated fluorocarbons (CFCs) are also ozone depleters. As the ozone layer in the earth s atmosphere screens out the harmful part of ultraviolet radiation in sunlight, ozone depletion is a matter of serious concern. The chemical industry must therefore look... 

---