Fractional yields of intermediates

Figure 5. Fractional yields of intermediates for the E2AdE3 model (0.5M 1-propanol reactant/ 5mM sulfuric acid catalyst at 375 C/ 34.5 MPa).

The reactions of B and R in the film are thereby determined directly, so that the instantaneous fractional yield of intermediate R with respect to the liquid phase reagent B is given by... 

The equations derived earlier for the effluent concentrations in the PFR and CSTR cases may be substituted into equation 9.2.1 to obtain numerical values of the fractional yield of the intermediate V as a function of the fraction of... 

Yield of intermediate versus fraction conversion for k"/k" = 5. Upper curve ri = 1 lower curve r < 0.3. 

The kinetic partitioning of enzyme intermediates is an important principle, and the rules governing kinetic partitioning are quite simple. The fractional yield of a given reaction is given simply as the rate of the desired reaction divided by the sum of the rates of all reactions involving the intermediate. For example, consider the forked reaction pathway in Scheme XXI. 

According to this mechanism, the fractional yield of the intermediate to form P is given by the ratio 2/( 2 + -1 + 3)- The importance of kinetic partitioning will be illustrated by two examples. 

Fig. 14. Yield of intermediate product A2 for the consecutive reaction scheme At - A2 - A3. (a) Calculated fractional yield of A2 as a function of conversion of Aj. (b) Dependence of the yield of butadiene on iron oxide catalyst particle size at 620°C (Adapted from Voge and Morgan, 1972).

There are several approaches [4, 25] that try to determine the fraction of spin-correlated radical ion pairs in radiolysis. The transient emission and absorption [25] suffer, however, from the lack of exact data on the extinction coefficients and luminescence quantum yields of intermediate products. The magnetic field effect technique [4] is more straightforward. However, it requires a detailed knowledge of spin evolution in zero field which is a problem in most cases. 

When the monomer is irradiated in a solvent such as water or alcohol, the radical or ionic intermediates formed from both the monomer and the solvent may initiate polymerization. The yield of initiating particles, to a first approximation, is expected to be proportional to the sum of the yields of intermediates in the irradiation of pure monomer or solvent, respectively, multiplied by their electron fractions (linear mixing rule, see O Eqs. (23.3) and (O 23.4) in O Sect. 23.3.1). In practice, however, the yield of initiation may be lower or higher than it is expected assuming linearity. This is due to energy or charge transfer between the components of the mixture. In dilute solutions (e.g., in water) it is commonly assumed that initiation occurs only by the intermediates of the solvent decomposition. 

Yields must be estimated as a preliminary step in the computations. These can be determined by the general methods outlined in Chap. 4, but it should be recalled that maximum yields cannot be obtained (perfect fractionation) unless an infinite number of trays and infinite reflux are employed- Thus, the plant yields will be slightly different from those determined in Chap. 4—9. slightly lower yield of top product and different yields of intermediate produces because of the overlap of the products. 

Carry out a second run with the recovered chloroform-alcohol mixture (A) add 100 g. of dry chloroform and sufficient super-dry ethyl alcohol (200-250 ml.) to give a total volume of 750 ml. Add 52 g. of sodium as before. Remove the excess of chloroform and attohol as before on a water bath through a fractionating column, add the intermediate fraction (B) from the first run, and fractionate again. The yield of product b.p. 144-146°, is 45 g. 

Optimal for single-hatch operation. For the sake of simplicity suppose that (1) the performance of an equipment unit is the fraction of the feed material converted to the material that is suitable for the next stage (e.g. the yield of the desired intermediate or final product), and (2) that the objective function is the amount of suitable material produced per unit time. Let us consider the situation shown in Fig. 7.4-5. On completion of cleaning at time ta processing of a batch begins. This processing is characterized by the performance curve/(r), e.g. the yield or conversion versus time relationship. The objective function F is defined as ... 

The influence of dispersion on the yield of an intermediate produced in a series reaction has also been studied. When 3 JuL is less than 0.05, Tichacek s results (22) indicate that the fractional decrease in the maximum amount of intermediate formed relative to plug flow conditions is approximated by l/uL itself. Results obtained at higher dispersion numbers are given in the original article. 

Figure 12.13 contains a plot of the yield of the intermediate V as a function of the fraction A reacted for a value of kjk2 equal to 5. In this case, we see that the maximum yield of V based on the initial concentration of A is equal to 66.9%. 

Fig. 2 shows [Pd/Ba] as a function of [Sr/Ba] with our new data by Subaru HDS. By definition, [Sr/Ba] should increase with the fractional contribution of weak r-process to the stellar abundances. If Pd originates from weak r like Sr, [Pd/Ba] must show a correlation with the slope of unity to [Sr/Ba]. If Pd comes from main r like Ba, [Pd/Ba] must be constant. New data show a mild correlation with the slope less than unity, suggesting that the weak r-process fraction for Pd takes intermediate value between those of Sr and Ba 10%. Therefore, this implies that the weak r-process yield decreases gradually from Sr to Ba. 

Heating the reaction for shorter periods gave erratic results. At this point the semisolid mixture can be diluted with 200 ml. of water, extracted with benzene, and the benzene extract fractionally distilled to give ethyl 2,3-dicyano-3-methylpentanoate, b.p. 146.0-147.5° (2.5 mm.), m27d 1.4429 (highly purified ester has b.p. 138.5-141.5° (2 mm.), 25d 1.4432). The overall yield of a-ethyl-a-methylsuccinic acid is decreased by about 5% when the dicyano intermediate is isolated. 

The preparation described here of 3-cyclopentene-1-carboxylic acid from dimethyl malonate and cis-1,4-dichloro-2-butene is an optimized version of a method reported earlier3 for obtaining this often used and versatile building block.6 The procedure is simple and efficient and requires only standard laboratory equipment. 3-Cyclopentene-1-carboxylic acid has previously been prepared through reaction of diethyl malonate with cis-1,4-dichloro(or dibromo)-2-butene in the presence of ethanolic sodium ethoxide, followed by hydrolysis of the isolated diethyl 3-cyclopentene-1,1-dicarboxylate intermediate, fractional recrystallization of the resultant diacid to remove the unwanted vinylcyclopropyl isomer, and finally decarboxylation.2>7 Alternatively, this compound can be obtained from the vinylcyclopropyl isomer (prepared from diethyl malonate and trans-1,4-dichloro-2-butene)8 or from cyclopentadiene9 or cyclopentene.10 In comparison with the present procedure, however, all these methods suffer from poor selectivity, low yields, length, or need of special equipment or reagents, if not a combination of these drawbacks. 

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