Rapid injection experiments

Under the conditions of a rapid injection experiment, the conjugate addition reactions of Gilman reagents (177) (X = CN or I) with cyclohex-2-enone has been studied in detail. Formation of various species (178-181) and the oscillation of their concentrations have been monitored by XH NMR spectroscopy (Scheme 9).212... 

Levenspiel and Smith Chem. Eng. Sci., 6 (227), 1957] have reported the data below for a residence time experiment involving a length of 2.85 cm diameter pyrex tubing. A volume of KMn04 solution that would fill 2.54 cm of the tube was rapidly injected into a water stream with a linear velocity of 35.7 cm/sec. A photoelectric cell 2.74 m downstream from the injection point is used to monitor the local KMn04 concentration. Use slope, variance, and maximum concentration approaches to determine the dispersion parameter. What is the mean residence time of the fluid ... 

Levenspiel and Smith (1957) conducted an experiment with a 2.85cm diameter (internal) tube. 16.2 cm3 of a solution of KMnC>4 was rapidly injected into a water stream which flowed through the tube at a velocity of 0.357 m s-1. A photoelectric cell positioned 2.75 m downstream from the injection point was used to monitor the effluent concentration (cKMn04) from the tube. Determine, using the data given below,... 

Arnett and coworkers later examined the reaction of lithium pinacolone enoiate with substituted benzaldehydes in THE at 25 °C. The determination of the heat of reaction indicated that the Hammett p value for the process is 331. Although the aldol reaction was instantaneous in THF at 25 °C, the reaction with o- or p-methylbenzaldehyde could be followed using a rapid injection NMR method in methylcyclohexane solvent at —80 °C. Application of Eberson s criterion based on the Marcus equation, which relates the free energy of ET determined electrochemically and the free energy of activation determined by kinetics, revealed that the barriers for the ET mechanism should be unacceptably high. They concluded that the reaction proceeds via the polar mechanism . Consistent with the polar mechanism, cyclizable probe experiments were negative . The mechanistic discrepancy between the reactions of benzaldehyde and benzophenone was later solved by carbon kinetic isotope effect study vide infraf. ... 

Figure 24-16 shows effects of operating parameters in split and splitless injections. Experiment A is a standard split injection with brisk flow through the split vent in Figure 24-15. The column was kept at 75"C. The injection liner was purged rapidly by carrier gas, and peaks are quite sharp. Experiment B shows the same sample injected in the same way, except the split vent was closed. Then the injection liner was purged slowly, and sample was applied to the column over a long time. Peaks are broad, and they tail badly because fresh carrier gas continuously mixes with vapor in the injector, making it more and more dilute but never completely flushing the sample from the injector. Peak areas in B are much greater than those in A because the entire sample reaches the column in B, whereas only a small fraction of sample reaches the column in A.

A tee intersection, double tee, or a tee interseetion operated in a pinched format are the most popular choices for injection schemes in microfluidie formats due to their simplicity and ability to deliver time-independent concentrations of samples. These types of injection formats are unique to microfluidic devices. While short and rapid injections are needed in CE experiments, long loading times are regularly used with these injection systems even with high-speed separations since (ideally) no sample enters the separation channel until analysis begins. 

A different multiplexing method was proposed by McLean and RusseUf utilizing rapid injection of ions into the drift tube at a frequency much faster than could be processed by a stand-alone IMS using one-dimensional time correlation creating a pseudo-continuous ion beam within the drift tube. In this instrumental arrangement, a TOFMS was utilized as a rapid and sensitive detector since both IMS and TOFMS achieve separation based on time dispersion of ions. Correlated multiplexed data acquisition allowed the use of ion injection rates much faster than that predicted to achieve 100% duty cycle in a sequential pulse-and-wait experiment, and improved usage of the bidimensional separation space. 

In all experiments the CMT ran as planned. There were no problems with rapid condensation in the CMT, such as was seen in the earlier passive safety injection experiments in PACTEL. The main reason was the new CMT arrangement, with a flow distributor (sparger) installed to the CMT. The sparger spread incoming flow to the CMT horizontally, and the breakdown of the saturated water layer due to incoming water was not possible. The hot liquid layer between the steam and cold water in the CMT remained stable, even in the experiments where the hot liquid layer was less than 5 cm thick. 

Heat transfer between gas and sohds is exceedingly hard to measure because it is so rapid. Although the coefficient is low, the available surface area and the relative specific heat of solid to gas are so large that temperature equilibration occurs almost instantaneously. Experiments on injection of argon plasmas into fluidized beds have shown quenching rates of up to fifty million degrees Kelvin per second. Thus, in a properly designed bed, gas to solids heat transfer is not normally a matter of concern. 

After rapid intravenous injection of an opioid, the user experiences warm skin flushing and a rush that lasts about 45 seconds. In one retrospective study... 

---