Rearrangements Christmas

The kinetics for the Christmas rearrangement of 9-benzyl- and of variously 4-substituted 9-phenyl-8-azapurine-6-thiones were found to be first order, and the rate constants and equilibrium constants were recorded. A plot of log forward component versus Hammett s sigma values for the 4-phenyl substituents was rectilinear. The 8-azapurine isomer was disfavored by electron-withdrawing substituents and by increased temperatures. In dimethyl sulfoxide, the equilibrium favored the 8-azapurine isomer more than in alcohols. Ultraviolet monitoring of the reaction, in both directions, detected no buildup of any acyclic intermediate." ... 

Brine Staging Velocity past the membrane is important. If too low, polarization is excessive, local O rises, and rejection declines. Fouling occurs faster. If too high, pressure losses are higher than they need be, and the osmotic pinch is premature. Since the volume of feed declines continuously, the hydraulic design needs periodic rearrangement. This is commonly done as shown in Fig. 22-64, sometimes known as a Christmas tree. This design is commonly used where the fluid is pumped once, as in RO, NF, and gas-separation systems, but not where recirculation is practiced, as in ultrafiltration. 

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