Measures against Deterioration

In contrast to the P-N bond in alkylamino phosphines, the P-N bond in (l-pyrrolyl)phosphines seems to be rather stable toward solvolysis with protic reagents. However, they are easily oxidized with oxygen to produce the corresponding phosphine oxides [48, 49]. P(pyrrolyl)3, which has been frequently investigated for hydroformylation reactions, can even be recrystallized from methanol without decomposition [49]. The high stability toward protic reagents 

Noteworthy, however, researchers at BASF found that P(pyrrolyl)3 prepared on the basis of a protocol by Moloy and Petersen [8] became colored within 5 days under argon [13]. After 8weeks, a tear-like material was formed, which was useless in catalysis. In contrast, phosphoramidite 1 was not affected when a solution in CH2CI2 was washed with warm water. No color change took place when the material was stored under light for 4 weeks. 

Apparently, benzo-anellation of pyrrol is advantageous for the long-term stability of phosphoramidites. Thus, an analog binaphthol-based hgand claimed by Du Pont [10], which was used for comparison, decomposed to an extent of approximately 20% within 10 days of storage at room temperature under argon. 

When this ligand was used in hydroformylation under normal conditions, only 20% conversion was observed. Parallel to this, chemoselectivity toward the formation of the aldehyde and the regioselectivity were affected. 

A similar stabilizing effect by substitution of the heterocycle was found with tris(indolyl)phosphine [50]. In contrast to tris(pyrrolyl)phosphine, which decomposed within 8 weeks, the indolyl derivative was not affected by heating or by treatment with water. Only strong bases can substitute the pyrrol substituents. The same applies to strong acids. 

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However, the actual change observed when measured against the method value would be much more significant. This problem is widespread in analytical methods particularly for factors that are optimised and thus changes to either side of the method value are likely to cause deterioration in the method s performance. 

Once the column is bolted up (either after initial construction or after a shutdown), a number of operations are performed to prepare it for startup. This phase is often referred to as column commissioning. The main objectives of column commissioning are to clear the system of undesirable materials, to test the column and rectify potential problems, and to take preventive measures against performance deterioration (e.g. due to fouling). 

Appropriate procedures are prepared and approved describing the measures to be taken to protect the systems against deterioration. 

To determine the deterioration in component performance and efficiency, the values must be corrected to a reference plane. These corrected measurements will be referenced to different reference planes depending upon the point, which is being investigated. Corrected values can further be adjusted to a transposed design value to properly evaluate the deterioration of any given component. Transposed data points are very dependent on the characteristics of the components performance curves. To determine the characteristics of these curves, raw data points must be corrected and then plotted against representative nondimensional parameters. It is for this reason that we must evaluate the turbine train while its characteristics have not been altered due to component deterioration. If component data were available from the manufacturer, the task would be greatly reduced. 

The production manager and quality control manager should share a joint responsibility to establish and to authorize written procedures, to monitor and control the manufacturing environment, plant cleanliness and production validation to calibrate measuring devices, to train personnel., to protect products and materials against spoilage and deterioration and to maintain records. 

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