Instantaneous purities, preparative

Also shown in Figure 2 are the locations of two cut points defined by the instantaneous purities Pu and Pd, where P is the mass fraction of desired component. It should be noted that on-line species-specific detection for determining cut points is particularly useful in displacement chromatography since the formation of bands in close proximity to each other makes nonspecific detection (e.g., the monitoring of UV absorbance) ineffective. Note also that fixed values for Pu and Pd will in general not correspond to a fixed value for the purity of the product fraction, which is presumed to be measured off-line and will be denoted by the symbol Pp. For example, if the concentration of the desired component in the feed tank to the preparative column is reduced or if the relative sensitivity of the monitoring method to the impurities decreases, the values of Pu and Pd used to define cut points would have to be increased if the desired average purity for the entire product fraction is to be maintained. 

The anhydrous salt is prepared by several methods, eg, by reacting ZrCl with liquid anhydrous HP. It is necessary to use an excess of HP which also acts as a wetting agent. The reaction is instantaneous and is carried out in a polyethylene jar or carboy. When the evolution of HCl ceases, the material is transferred to a tray and dried under an atmosphere of nitrogen. By proper selection of equipment, purification of raw material, and drying conditions, materials of spectrographic purity can be produced (4). 

Oxabicyclo[3.2.0]hepta-l,4,6-triene (289), a planar Sn-electron analog of 4, has been prepared by flow pyrolysis of 288 (both cis and trans) in approximately 10% yield (>95% purity) 289 is an extremely sensitive compound, polymerizing instantaneously on exposure to oxygen. In solution, where it is stable for several days, it slowly dimerizes to give the known compound 291 the pentacyclic intermediate 290 is possibly involved. In Diels-Alder reactions, 289 behaves like an olefin with cyclopentadiene it reacts immediately to give 292. Hydrogenation occurs at the same site. ... 

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