Organic reactions—continued thermodynamics

We cover each of these types of examples in separate chapters of this book, but there is a clear connection as well. In all of these examples, the main factor that maintains thermodynamic disequilibrium is the living biosphere. Without the biosphere, some abiotic photochemical reactions would proceed, as would reactions associated with volcanism. But without the continuous production of oxygen in photosynthesis, various oxidation processes (e.g., with reduced organic matter at the Earth s surface, reduced sulfur or iron compounds in rocks and sediments) would consume free O2 and move the atmosphere towards thermodynamic equilibrium. The present-day chemical functioning of the planet is thus intimately tied to the biosphere. 

In natural waters organisms and their abiotic environment are interrelated and interact upon each other. Such ecological systems are never in equilibrium because of the continuous input of solar energy (photosynthesis) necessary to maintain life. Free energy concepts can only describe the thermodynamically stable state and characterize the direction and extent of processes that are approaching equilibrium. Discrepancies between predicted equilibrium calculations and the available data of the real systems give valuable insight into those cases where chemical reactions are not understood sufficiently, where nonequilibrium conditions prevail, or where the analytical data are not sufficiently accurate or specific. Such discrepancies thus provide an incentive for future research and the development of more refined models. 

A relevant characteristic of the technology should be the ability to remove the water selectively and continuously in order to shift the chemical equilibrium to full conversion. Because the presence of a liquid water phase will lead to rapid deactivation of the solid catalyst, operating conditions for water-free organic liquid should be found. In addition, the thermodynamic behavior of the reaction mixture is nonideal, particularly with respect to the couple alcohol-water. 

In order to remain alive, in other words, organisms must be in a perpetual state of activity (their cells work even when they sleep), and must continuously pump out the excess entropy of their reactions. In the words of Erwin Schrodinger (1944), they eat not only matter but also order. Towards the end of the nineteenth century, in conclusion, a living organism came to be seen essentially as a thermodynamic machine, i.e. as a chemical machine that must be continuously active in order to obey the laws of thermodynamics. 

Some structures can only originate in a dissipative (nonequilibrium) medium and be maintained by a continuous supply of energy and matter. Such dissipative structures exist only within narrow limits due to the delicate balance between reaction rates and diffusion. If one of these factors is changed, then the balance is affected and the whole organized structure collapses. In a system of two simultaneous reactions, thermodynamic coupling allows one of the reactions to progress in a direction contrary to that imposed by its own affinity, provided that the total dissipation is positive. 

The first three reactions are considered at present as phylogenetically ancient and known from extant organisms. The remaining redox transformations are thermodynamically possible but still not carried out experimentally, perhaps due to kinetic limitations. In addition, even if such reactions did occur in the early Earth, their continuation would be constrained by electron-acceptor recycling. As an assumption. 

Thermodynamically stable microemulsions and kinetically stable emulsions may be utilized to bring water and nonvolatile hydrophilic substances, such as proteins, ions, and catalysts, into contact with a SCF-continuous phase (e.g. CO2) for separation, reaction and materials formation processes. Reactions between hydrophilic and hydrophobic substrates may be accomplished in these colloids without requiring toxic organic solvents or phase transfer catalysts. CO2 and aqueous phases may be mixed together over a wide range in composition in w/c and c/w emulsions. The emulsion is easily broken by decreasing the pressure to separate the water and CO2 phases, facilitating product recovery and CO2 recycle. Reaction rates can be enhanced due to the considerably lower microviscosity in a w/c as compared to a water-in-alkane microemulsion or emulsion. 

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