Continuous-flow apparatus

Figure 5.4-1 Continuous flow apparatus as used for the hydroformylation of 1-octene in the...

However, attempts to reuse the ionic catalyst solution in consecutive batches failed. While the products could readily be isolated after the reaction by extraction with SCCO2, the active nickel species deactivated rapidly within three to four batch-wise cycles. The fact that no such deactivation was observed in later experiments with the continuous flow apparatus described below (see Figure 5.4-2) clearly indicate the deactivation of the chiral Ni-catalyst being mainly related to the instability of the active species in the absence of substrate. 

Figure 5.4-2 Schematic view of the continuous flow apparatus used for the enantioselective...

The process which seems to have the most possibilities for a scale-up development is that using a low amount of graphite, for which the desorption treatment can be totally suppressed in a continuous flow system. We recently proposed the use of such a process to perform FC acylations under the action of MW with FeCl3 as catalyst [76 d]. The replacement of FeCl3 by a graphite bed is quite conceivable in the same continuous flow apparatus. 

Volume, V, of the dissolution medium in a batch-type apparatus (Eq. 31), or volume flow rate, dV/dt, in a continuous-flow apparatus (Eq. 

Scheme 13. Continuous flow apparatus for the HKR of 4-hydroxy butene oxide over silica bound Co(salen) complex 37.

Fig. 1. Continuous-flow-apparatus for the optimization of homogeneous catalytic processes. A, catalyst solution B, starting compounds C, thermostated reactor D, trap E, gas-chromatograph F, data evaluation.

A comparison of a series of [YCo(cod)] catalysts in the test reaction (Scheme 5) under identical conditions in the continuous-flow apparatus (Fig. 1) has revealed that the reaction temperature required for 65% pro-pyne conversion depends on the nature of the controlling ligand Y. Further, an inspection of Table VIII reveals that both the Arrhenius energy of activation Ea for the reaction and the selectivity of the catalyst are strongly controlled by the ligand Y [85AG264, 85AG(E)248]. 

In the direct calorimetric determination (-AH = f(njj), the amount adsorbed (nj is calculated either from the variations of the gas pressure in a known volume (volumetric determination) or from variations of the weight of the catalyst sample in a static or continuous-flow apparatus (gravimetric determination), or from variations of the intensity of a mass spectrometer signal [151]. 

Figure 5.4-2 Schematic view of the continuous flow apparatus used for the enantioselective hydrovinylation of styrene in the biphasic [EMIM][(CF3S02)2N] system. The components are labeled (alphabetically) as follows C compressor, CT cold trap, D dosimeter, DP depres-surizer, F flow-meter, M mixer, MF metal filter, P HPLC pump, PT pressure transducer and thermocouple, R reactor, S styrene.

Figure 15.1 illustrates a simplified continuous flow apparatus. Figure... 

Figure 15.3 Adsorption and desorption peaks in a continuous flow apparatus.

For maximum accuracy, the manifold and calibrated volumes in a volumetric apparatus should be maintained at constant temperature. Thermostating is not necessary for vacuum micro balances but in helical spring balances the spring should be maintained at constant temperature. Continuous flow apparatus need not be thermostated since the signals are immediately calibrated with known volumes at the same temperature and pressure. However, ambient temperature and pressure must be known to insure accurate calibration. 

Because the gravimetric and volumetric apparatus use vacuum systems it is convenient to outgas by vacuum. Outgassing in a continuous flow apparatus is accomplished by purging. 

The stopped-flow method is a routine laboratory tool, whereas the continuous-flow apparatus is used in a few specialized cases only. The stopped-flow technique requires only 100 to 400 /XL of solution or less for the complete time course of a reaction the dead time is as low as 0.5 ms or so and observations may be extended to several minutes. Stopped flow does, however, require a rapid detection and recording system. 

The simplest form of the method is to submerge the end of the observation tube of a continuous-flow apparatus in a beaker of acid. A somewhat more sophisticated version is illustrated in Figure 4.4. A third syringe mixes the quenching acid with the reagent solutions via a second mixing chamber. Such an apparatus... 

Milk thistle seed extraction experiments were carried out with hot water at 100,120, and 140°C using the same water flow rate (0.30 mL/min) and seed meal particle size (0.4 mm). The pressures employed in the experiments at these temperatures were approx 1, 4, and 5 atm, respectively. Figure 3 shows results from typical runs at 100,120, and 140°C, where the compound concentrations from the collected water (methanol added for solubilization is subtracted out) in each sample aliquot from the continuous flow apparatus are plotted as a function of time. Thus, the concentrations presented represent the average concentrations of the four main extracted compounds in an aliquot. As noted in Fig. 3, the concentrations of each of the compounds reached a maximum after a few minutes of extraction time and then fell exponentially with time as the extracted material was removed from the solid sample. The time for obtaining the maximum compound concentration decreased with temperature. 

Fig. 11. Schematic diagram of continuous flow apparatus and structure of an enzymatically coupled FET. (a) Schematic diagram of continuous flow apparams S, enzymatically coupled FET sensor SC, sensor cell WB, water bath D, drtdnage P, peristaltic pump TV, three-way joint EV, electrical valve VC, valve controller WS, washing solution AS, analyte solution, (b) Detailed structure of flow-through cell OR, rubber O-ring. (c) Structure of enzymatically coupled FET (electrical insulation with epoxy resin is not shown here for simplicity) ISFET, ion-sensitive FET EM, enzyme membrane G, thin gold film TC, card edge connector. (Reproduced from Shiono et al. (9), with permission.)...

Stopped flow and continuous flow methods [11] have been used to follow proton transfer reactions with half-lives in the millisecond range. The stopped flow method which is more popular is essentially a device for mixing the reactants rapidly (typically in one millisecond) together with some means of observing the fast reaction which follows. Proton transfer from p-nitrobenzyl cyanide to ethoxide ion in ethanol/ether mixtures at —77 °C was studied in this way [12]. The reaction was followed spectrophotometrically. The most rapid reaction occurred with ti/2 ca. 2 x 10 2 sec although the equipment was suitable for following reactions with f1/2 ca. 2 x 10 3 sec. A similar method has been used to measure rates of proton transfer between weak carbon acids (for example, triphenylmethane) and bases (for example, alkoxide ions) in dimethyl sulphoxide [13], A continuous flow apparatus with spectrophotometric detection was used [14] to measure rates of ionization for substituted azulenes in aqueous solution (4), reactions for which half-lives between 2 and 70 msec were observed. 

Tingstad, J.E. Riegelman, S.J. Dissolution rate studies I design and evaluation of a continuous flow apparatus. J. Pharm. Sci. 1970, 59, 692-696. 

Supported platinum, rhodium, and ruthenium complex catalysts have been used extensively in the reaction of trisubstituted silanes with acetylene in the gas phase, predominantly in a continuous-flow apparatus. Formation of a polymer layer on the surface after immobilization of the platinum complex has protected the catalyst against leaching in long-term hydrosilylation tests [91]. 

Currently, the most important uses of hydrodynamic voltammetry include (1) detection and determination of chemical species as they exit from chromatographic columns or a continuous-flow apparatus (2) routine determination of oxygen and certain species of biochemical interest, such as glucose, lactate, and sucrose (3) detection of end points in coulometric and volumetric titrations and (4) fundamental studies of electrochemical processes. 

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