Cooling initiation

The procedure may be conducted on a larger scale in which case the proportion of catalyst and base are reduced. The submitters report that they obtained 169 g (78 ) of butyroin from 216.3 g (3.0 mol) of butyraldehyde, 26.8 (0.1 mol) of thiazolium catalyst, 60.6 g (0.6 mol) of triethylamlne, and 600 mL of absolute ethanol. Although the scale may be increased further, appropriate precautions should be taken to control the reaction. For example, the aldehyde may be added in portions or the flask may be cooled initially. 

This reaction mixture should not be cooled initially because an uncontrollable exothermic reaction will occur if a large concentration of alkoxide builds up. 

The use of tantalum wire along with the two-zone technique ensures a safe reaction rate. When the sulfur has reacted completely with the tantalum wire (usually within 7-10 days) the ampule is removed from the furnace, shaken vigorously to break up clumps of unreacted material, and placed in the center of me furnace. It may be necessary to repeat this procedure several times to ensure that all the wire has reacted. After 1 or 2 days at 850-900°, the cooling process may be started. The sample is cooled initially to 750° and annealed for 1 day. It is then annealed at 650° for about a day and at 550° for another 2 to 3 days. The furnace is then shut off and the sample is allowed to cool for 5-6 hours to room temperature. 

Method B b 2,4,6-Trichloro-1,3,5-triazine (1 200g, 1.08 mol) was placed in a polyethylene bottle, cooled initially in a dry ice/acctone bath and anhyd HF was condensed from a cylinder. As the HF began to condense the 2,4,6-trichloro-1,3,5-triazine (1) slowly dissolved. A magnetic stirring bar (Teflon coated) was added and the cooled (ice bath) mixture was stirred with continuous introduction of HF until all the... 

Recall that from the definition of spin temperature a low temperature implies large polarization of the magnetic moments. Thus, low carbon spin temperature is what is desirable just before inducing an FID. Because in the basic cross polarization experiment as described you can gain S/N according to the ratio Tp/T, the improvement depends on how well the protons are cooled initially. Some of the methods commonly used to do this will be described later in this section. 

Alternatively, toluene can be first charged into a reaction flask, and then nitric acid is added portion-wise with stirring and cooling. Initially, the reaction rate is slow, and it dramatically increases when the temperature of reaction solution reaches certain values like 30-40 °C, which in turn would increase the reaction temperature enormously. However, if too much nitric acid is added at the beginning, it will be extremely diflicult to control the reaction rate and temperature. The explosion properties of explosives prepared through different charging sequences appear to be quite similar, as illustrated in Table 7.32. 

Following certain DBEs (feedwater line break, small break LOCA, steam line break, or loss of offsite power), shutdown cooling can be initiated with RCS hot leg conditions which exceed the normal shutdown cooling initiation temperature of 350 F. However, shutdown cooling will never be initiated at conditions which exceed the design temperature of the SCS components. 

As direct on-column injection can lead to a relatively rapid deterioration of the column through interactions of the liquid phase and the injection solvent or involatile impurities in the sample, an alternative has been devised in which a specially designed injection port takes over the function of the top part of the column. The sample is introduced into this inlet, which is cooled initially, and then its temperature is raised at a controlled rate so that the sample components are selectively vaporised. Injection systems of this type are relatively new and appear to be well suited to the analysis of lipids of high molecular weight, such as intact triacylglycerols. This is discussed further in Chapter 8. 

In the laboratory preparation of diketene the mixture of ketene, unchanged acetone, and methane from a ketene generator is passed into a condensing system which is cooled initially in Dry Ice, and the condensate is allowed to warm to room temperature over a period of about twenty-four hours. The resulting mixture of acetone, diketene, and dehydracetic acid is separated by distillation under reduced pressure (50-55% of diketene). More exact control of the concentration and... 

Welsch et al" used gas chromatography combined with accumulated dosage to determine volatiles. Volatiles from a heated sample are transferred in a carrier gas stream to a cooled initial part of the GC column and are subsequently discharged onto the column by heating. The products were identified by mass spectrometry. 

To cool initial mass of vapor to final state.-16.5 w... 

Early in the twentieth century, it was recognized that aqueous solutions of surface-active agents do not follow the patterns of solution behavior common to most solutes as their concentration is increased. It was suggested that the unusual behavior of smfactants could be attributed to the aggregation of individual molecules into clusters in solution above a fairly well-defined concentration. Although that somewhat radical idea received a rather cool initial reception, the concept of... 

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