Thermodynamically controlled reactions sulfation

Important in this quite general strategy is that, for practically all instances, die reaction is under thermodynamic control, and the control of the stoichiometry is extremely difficult It follows that only the more stable acetals are produced (see Sec. H.B) and usually multiacetals are obtained if several hydroxyl groups are available within die same molecule. This has been a major concern in acetalation reactions in neutral conditions. For instance, use of copper(II)sulfate either in acetone alone or in N, N-dunethylformamide without any additional catalyst leads to acetals with structures that differ from those resulting from reactions in the presence of an acid The reaction depends on the temperature [31] however, the strict neutrality of a medium in which copper(II)sulfate and polyols are interacting can be questioned. 

If one of the kinetic factors approaches zero first, the reaction rate is said to be kinetically controlled if the thermodynamic factor falls first, the control is thermodynamic. The aerobic consumption of organic species and highly reduced compounds such as H2(aq) and H2S(aq) invariably show kinetic controls, because the thermodynamic drive for the oxidation of these compounds is quite large. Since methanogens and sulfate reducers operate under a considerably smaller thermodynamic drive, in contrast, it is not uncommon for their reaction rates to be controlled thermodynamically. 

Both resistance of the electrolyte and polarization of the electrodes limit the magnitude of current produced by a galvanic cell. For local-action cells on the surface of a metal, electrodes are in close proximity to each other consequently, resistance of the electrolyte is usually a secondary factor compared to the more important factor of polarization. When polarization occurs mostly at the anodes, the corrosion reaction is said to be anodically controlled (see Fig. 5.7). Under anodic control, the corrosion potential is close to the thermodynamic potential of the cathode. A practical example is impure lead immersed in sulfuric add, where a lead sulfate film covers the anodic areas and exposes cathodic impurities, such as copper. Other examples are magnesium exposed to natural waters and iron immersed in a chromate solution. 

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