Reaction completion time

Reaction complete Reduce time until conversion is still complete to maximize 

In autocatalytic reaction the graph plotted between the rate of reaction and time shows a sigmoid curve as shown in Fig. 6.1. As the product (catalyst) concentration increases the rate increases, and reaches to a maximum when the reaction is complete. 

Fitting data for the fraction of a reaction complete as a function of time to the kinetic models is often 

It should be pointed out that many of these reports compared reaction times of MW heated reactions with times previously reported in the literature for the same reactions under conventional heating. Unfortunately the conventionally heated reactions are often complete in times which are much shorter than those quoted and it is important to perform direct and careful comparisons between MW and thermal reactions, using the same quantities of reagents and solvents and the same reaction temperature. 

Table Al.l Extent of reaction completion for a first order reaction at different time intervals corresponding to different multiples of x and tll2

Note. Substrate variation resulted in reaction times of 3-80 h, with reaction completion being monitored by g.l.c. 

AP, is 20.8 kPa after 665 s. If only ether is present initially, and the increase in pressure after a long time (reaction complete) is 82.5 kPa, what is the partial pressure of ether, pe, after 665 s State any assumptions made. 

Figure 5-25B. For a first order reaction, the ratio of time in a continuous tank to the time in a batch tank for various percentages of reaction completion. By permission, Oidshue, J. Y. [29].

The two time constants x and tV2 define time intervals in which a specific extent of reaction has been completed. In some applications one may wish to define a time point associated with a certain other extent of reaction completion. That is, how much time is required for the reaction to go to, say, 75% or 90% completion. This can be calculated using rearranged forms of Equations (A.16) through (A.21). For convenience, in Table Al.l we tabulate the extent of reaction completion for different time intervals, as multiples of x and ty2. 

Reaction time is extremely important in avoiding the side reaction illustrated in Eq. (1.1), where the nitroalkane product reacts with nitrite anion and any nitrite ester, formed as byproduct, to give a pseudonitrole. The reaction of sodium nitrite with alkyl halides is much faster than this competing nitrosation side reaction, even so, prompt work-up on reaction completion is essential for obtaining good yields. 

This method is similar to continuous flow method except that the rate of flow is continuously varied and the analysis is made at a fixed point along the observation tube. Since the rate of flow changes with time, the reaction mixtures arriving at observation point have different time. In the accelerated flow method the output from a photo electric colorimeter is fed to a cathode-ray oscilloscope, which sweeps out a complete time-concentration record which may be photographed. The method is useful for very rapid enzyme reactions and requires only small quantities of reactants. 

With the availability of numerical ODE solvers, exercises of the kind just presented are superfluous. While the results are the same for large parts of the data, numerical integration delivers a complete analysis that covers the whole reaction from time 0 to the end. 

Therefore, to obtain complete stereoselectivity, the entire glycosylation process has to be performed in a highly controlled manner. In this particular case, the control is achieved by the use of extremely mild catalyst (I NBr), although very reactive substrates and prolonged reaction at times are required. 

Search for More Active Catalyst. An extensive screening effort was undertaken to find a catalyst more active than Et-DuPhos-Rh. As a result of this effort, Et-FerroTane-Rh and some other competitive catalysts were found. The reactivity of Et-FerroTane-Rh and Et-DuPhos-Rh, is presented in Figure 3.9. The reaction rate with Et-FerroTane-Rh catalyst is very high with a small induction period, and the total time for reaction completion is drastically less than with Et-DuPhos-Rh. 

---