Transformation of Organic Compounds

The term fermentation was obtained from the Latin verb fervere which describes the action of yeast or malt on sugar or fruit extracts and grain. The boiling is due to the production of carbon dioxide bubbles from the aqueous phase under the anaerobic catabolism of carbohydrates in the fermentation media. The art of fermentation is defined as the chemical transformation of organic compounds with the aid of enzymes. The ability of yeast to make alcohol was known to the Babylonians and Sumerians before 6000 bc. The Egyptians discovered the generation of carbon dioxide by brewer s yeast in the preparation... 

Minero, C., Mariella, G., Maurino, V., and Pelizzetti, E. (2000) Photocatalytic transformation of organic compounds in the presence of inorganic anions. 1. Hydroxyl-mediated and direct electron-transfer reactions of phenol on a titanium dioxide-fluoride system. Langmuir,... 

Arends, I.W.C.E., Sheldon, R.A., Wallau, M. and Schuchardt, U. (1997). Oxidative transformation of organic compounds mediated by redox molecular sieves. Angew... 

C. Minero, V. Maurino, E. Pelizzetti, Mechanism of the photocatalytic transformation of organic compounds, in V. Ramamurthy, K.S. Schanze (eds.), Semiconductor Photochemistry and Photophysics, Vol 10 of Molecular and Supramolecular Photochemistry, Marcel Dekker, New York, 2003, pp. 211-229. 

Most of the above reactions occur via a mechanism involving intermediates with a metal-silicon bond (i.e. silicometallics) and a metal-hydrogen bond, accompanied (or sided) only occasionally by compounds containing metal-carbon bonds (i.e. organometallics) that are characteristic of the key intermediates of transition-metal-catalyzed transformations of organic compounds (for recent reviews, see Refs [11, 13]). 

Chibata, 1. and Tosa, T. (1977) Transformation of organic compounds by immobihzed microbial cells, Appl. Microbiol., 22, 1-25. 

Problem 2.40 Which of the following transformations of organic compounds are oxidations, which are reductions, and which are neither ... 

Once upon a time. .. there was water. Long after enzymes began to be used for preparative-scale transformations of organic compounds, this peculiar solvent was still considered to be not only the most suitable but the only medium in which the natural biocatalysts could exert their activity. Then both scientific curiosity and practical problems (the need to overcome the poor solubility of most of the substrates in aqueous solutions) prompted different scientists to add small amounts of water-miscible organic solvents to the aqueous medium. And it worked in most cases the enzymes were still fully alive. 

Finally, compared to the chemical reactions discussed in the previous chapter, photochemical transformations of organic compounds usually exhibit a much weaker temperature dependence. Reactions of excited species in aqueous solutions have activation energies of between 10 and 30 kJ.mol-1 (Mill and Mabey, 1985). Hence, a 10°C increase (decrease) in temperature accelerates (slows down) a reaction only by a factor of between 1.15 and 1.5 (see Table 3.5). 

Biochemical transformations of organic compounds are especially important because many reactions, although thermodynamically feasible, occur extremely slowly due to kinetic limitations. For example, we might be interested in the question of whether benzene can be biodegraded under naturally occurring methanogenic conditions (see Illustrative Example 17.1). Such natural attenuation of this toxic aromatic substance may be thermodynamically allowed under the perceived conditions. But these conditions may not be accurate (e.g., the benzene and methane chemical activities in the system). Also other environmental factors may cause the rate to be unobservably slow. One possibility is that the relevant microorganisms are simply not active in the environment of interest. 

Other potential limitations may influence biological transformations of organic compounds. First, organic compound uptake by the isolated cells may be rate... 

An important focus of organometallic research has been the development and study of transition metal complexes as catalysts for transformations of organic compounds. These systems enable chemical reactions to occur under conditions that are often milder and more environmentally benign than more traditional routes, such as Lewis acid-catalyzed reactions, Grignard... 

Wackett, L. P., and C. D. Hershberger. 2001. Biocatalysis and Biodegradation Microbial Transformation of Organic Compounds. ASM Press, Washington, DC. 

IRREVERSIBLE TRANSFORMATIONS OF ORGANIC COMPOUNDS UNDER HIGH PRESSURES... 

The direct photolysis of compounds such as HONO, 03, HCHO, and N02 in the tropospheric gas phase is a very important source of reactive species, which are then involved in the transformation of organic compounds. Additionally, some organic molecules including organic pollutants undergo photolysis as a significant or even the main process of removal from the atmosphere. It is for instance the case for nitronaphthalenes, the atmospheric lifetime of which can be as low as a couple of hours because of direct photolysis [11, 12]. 

Equations 17.14 and 17.15) induced by the same classes of compounds already seen for particulate matter [46]. Transformation of organic compounds dissolved in water droplets can also take place because of reaction with the powerful oxidizing agent OH. This species can be produced on photolysis of H202 (see Equation 17.6, [12, 27]), nitrate (Reaction 17.16, which is also valid for aqueous solutions), and nitrite [47]. 

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