Rate profile for

Fig. 2.1. Rate profiles for nitration in 80-100% sulphuric acid. For references see table 3.3.

Fig. 3.3. Rate profiles for nitration at 25 °C corrected for variation in activity coefficients. ...

There are certain limitations to the usefulness of nitration in aqueous sulphuric acid. Because of the behaviour of the rate profile for benzene, comparisons should strictly be made below 68% sulphuric acid ( 2.5 fig. 2.5) rates relative to benzene vary in the range 68-80% sulphuric acid, and at the higher end of this range are not entirely measures of relative reactivity. For deactivated compounds this limitation is not very important, but for activated compounds it is linked with a fundamental limit to the significance of the concept of aromatic reactivity as already discussed ( 2.5), nitration in sulphuric acid cannot differentiate amongst compounds not less than about 38 times more reactive than benzene. At this point differentiation disappears because reactions occur at the encounter rate. 

Further problems arise if measurements of the rate of nitration have been made at temperatures other than 25 °C under these circumstances two procedures are feasible. The first is discussed in 8.2.2 below. In the second the rate profile for the compound imder investigation is corrected to 25 °C by use of the Arrhenius parameters, and then further corrected for protonation to give the calculated value of logio/i fb. at 25 °C, and thus the calculated rate profile for the free base at 25 °C. The obvious disadvantage is the inaccuracy which arises from the Arrhenius extrapolation, and the fact that, as mentioned above, it is not always known which acidity functions are appropriate. 

This method is exemplified by its application to quinoline, isoquinoline, cinnoline, and isoquinoline 2-oxide, which are nitrated as their conjugate acids. The rate profiles for these compounds and their N- or O-methyl perchlorates show closely parallel dependences upon acidity (fig. 2.4). Quaternisation had in each case only a small effect upon the rate, making the criterion a very reliable one. It has the additional advantage of being applicable at any temperature for which kinetic measurements can be made (table 8.1, sections B and D). 

For this series of compounds qualitative information is quite extensive. Application of the criteria discussed in 8.2, in particular comparison with the corresponding methyl quaternary salt, establishment of the rate profile for nitration in sulphuric acid, and consideration of the encounter rate and activation parameters, shows that 2,4,6-collidine is nitrated as its cation. The same is true for the 3-nitration of 2,4- ... 

Fig. 8. Drying time and rate profiles for leather pasted on glass plates and dried in two temperature stages. Gas velocity = 5 m/s in parallel flow, 71°C in the first stage, 57°C in the second. The falling rate, drying rate is proportional to residual moisture content.

Temperature reaction rate profiles for representatives compounds are available (21,26). Particularly important are the operating temperatures required before destmction is initiated. Chemical reactivity by compound class from high to low is (27) alcohols > cellsolves/dioxane... 

Fig. 8.6. pH-Rate profile for release of salicylic acid fiom benz-aldehyde disalicyl acetal. [Reproduced firom E. Anderson and T. H. Fife, J. Am. Chem. Soc. 95 6437 (1973) by permission of the American Chemical Society.]... 

Fig. 8.7. pH-Rate profile for compound 1. (Reproduced from Ref. 72 by permission of the American Chemical Society.)... 

Fig. 8.P21. pH-Rate profile for hydrolysis of A in buffered aqueous solution at 70 C.

Figure 8.P28 gives the pH-rate profile for conversion of the acid A to the anhydride B in aqueous solution. The reaction shows no sensitivity to buffer concentration. Notice that the reaction rate increases with the size of the alkyl substituent, and, in fact, the derivative with R = = CHj is still more reactive. Propose a mechanism which is... 

Figure 8.P31 gives the pH-rate profile for hydrolysis of thioesters A-D and shows a dependence on the nature of the substituents in the alkylthio group. Propose a mechanism which would account for the pH-rate profile of each compound. 

Figure S-I2. pH-rate profile for the reaetion of hydroxylamine with aeetone in water at 25°C. Dashed line rate of acid-eatalyzed dehydration step solid line observed rate.

Figure 6-8 is a pH-rate profile for the hydrolysis of p-nitrophenyl acetate. The slopes of the straight-line portions are —1,0, and -L 1, reading in the acid to base direction, and this system can be described by... 

Figure 6-13. pH-rate profile for the hydrolysis of trimethylacelylsalicylic acid at 25°C (aqueous solution containing 0.5% ethanol) (60). 

Figure 6-18 shows a bell-shaped pH-rate profile for the hydrolysis of monomethyl dihydrogen phosphate. Other examples are the hydrolysis of o-carboxyphenyl hydrogen succinate and the hydration of fumaric acid. ... 

A collection of pH-rate profiles for drug decomposition reactions has been published. ... 

The pH-rate profile for the hydration of 2-hydroxypteridine at 20° shown in Fig. 4 is typical for the heterocyclic acids listed in Table VI. Some representative values of and are given in Table VII. The function plotted in the figure follows from Eq. (18), and the deviations... 

Reaction rate profiles for methane-air mixture with <3> = 0.50 in 50 mm tube diameter (a) neglecting and (b) considering radiation heat transfer. 

According to the ethylene consumption rate profile for ethylene/l-hexene copolymerization in figure 1, it indicated that deactivation of active species occurred in the borate system. On the... 

If the formation and breakdown steps of a mechanism involving a tetrahedral intermediate respond differently to changes in pH or catalyst concentration, then one can find evidence from plots of rate versus pH or rate versus catalyst concentration for a change in rate determining step and thus for a multistep mechanism. An example would be the maximum seen in the pH rate profile for the formation of an imine from a weakly basic amine (such as hydroxylamine). On the alkaline side of the maximum, the rate determining step is the acid-catalyzed dehydration of the preformed carbinolamine on the acid side of the maximum, the rate determining step is the uncatalyzed addition of the amine to form the carbinolamine. The rate decreases on the acid side of the maximum because more and more of the amine is protonated and unable to react. 

FIGURE 7.17 pH-rate profile for quinone methide formation. 

The mechanistic interpretation of the pH-rate profiles for quinone methide disappearance relied on Hartree-Fock calculations with 6-31G basis sets as well as on product studies. In Fig. 7.20, we show the potential-density maps of the protonated and neutral pyridoindole quinone methide with negative charge density colored red and positive charge density colored blue. Inspection of the methide... 

FIGURE 7.18 pH-rate profile for the disappearance pyrrolo[l,2-a]indole quinone methide. 

FIGURE 7.25 pH-rate profile for prekinamycin quinone methide hydrolysis. 

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