Rates under-reporting

Although etch rate data for a particular polymer film yielded straight-line kinetic plots, the data from one film to another for any given polymer exhibited considerable scatter this is indicated by the large standard deviations in Tables I and II. Because of the scatter, the cause of which is under investigation, the etch rate data reported here have only semiquantitative significance. 

Some reports indicated that the Diels-Alder reaction could be done in aqueous environments with a potential for accelerated reaction rates under the right conditions (Rideout and Breslow, 1980 Blokzijl and Engberts, 1992 Pai and Smith, 1995 Otto et al., 1996 Wijnen and Engberts, 1997), and the addition of InCl3 was determined to act as a catalyst in aqueous environments (Loh et al., 1996). For a review of organic reactions that can be done in aqueous media, see Li (2005). 

Recently, Hajek and coworkers have reported results on microwave-assisted chemistry performed by cooling of a reaction mixture to as low as -176 °C. Reaction rates were recorded under microwave and conventional conditions. The higher reaction rates under microwave heating at sub-ambient temperatures were attributed to a superheating of the heterogeneous K10 catalyst [44],... 

Experimental studies of reaction kinetics are commonly carried out under conditions far from equilibrium, where the thermodynamic drive is strong and forward reaction overwhelms reverse. Rate laws reported in the literature, such as Equation 17.2, therefore, generally represent the forward reaction rate. The laws can be expressed in the general form,... 

The diagram shown in Fig. 20, which gives the log of the polymerization rate under steady-state conditions, plotted vs. the reciprocal of the absolute temperature, was drawn from the above data. The activation energy calculated from the data reported in Fig. 20 is about 10,000 cal./mol. 

Typical data are those reported for three scan rates under the experimental conditions given in Table 23.5. An average k of 9.7 s 1 was obtained. Note that in this case as well as in the following example, kobs is a pseudo-first-order rate constant and is equal to kc[Z], where Z (HY3" in this case) is the reagent reacting with B (Cd2+). 

Non-aminofunctional silanes did not show an observable methanol resonance after about 5-6 h when no catalyst was added. This suggests that hydrolysis was very slow under these conditions. An acid was added to aid in the hydrolysis of MPS, VS, GPS, and MrPS. The results show that the rate constant increases with a decrease in the pH of the solution, similar to previously reported results [16, 47]. The addition of HC1 also significantly increased the reaction rates, as reported by Pohl and Osterholtz for the hydrolysis of GPS in water [16]. 

The work described here was undertaken on the premise that measurements of the number of particles, total particle surface, and concentration of trapped radicals are needed in conjunction with rate measurements over a wide range of initiation rate and monomer concentration to understand more thoroughly the important factors in this type of heterogeneous polymerization. However, as will become apparent from the results reported here, variations in particle number and total surface are small and have little effect on the polymerization rate. Under our conditions trapped radicals were present in too low a concentration to be detected and cannot account for the peculiar features of the reaction kinetics. 

Another interesting feature of the study was the unreliability of the absolute number of individuals who self-reported cocaine use and the underestimation of cocaine use by urinalysis there is an approximately threefold under-reporting of cocaine use as compared to the positive rate by hair analysis, whereas the positive rate by unannounced urine testing was approximately half that of hair analysis. 

The effects of inhibitors such as NO and propylene are rather interesting. There have been a large number of papers on the effects of these inhibitors. Crawford and Steacie, working with NO + w-butane, found a maximal inhibition by NO at about 10 mole per cent. The rates under these conditions were not, however, very reproducible, and contrary to earlier reports gave a different product distribution from the uninhibited reactions. ... 

The number and variety of reported studies on the bro-mination of steroid ketones is so great [133] that it would be impossible to survey the field adequately in a small space. The situation is complicated by uncertainty in some early work as to whether the bromo-ketones are products of kinetic or thermodynamic control. It often happens that the initial product of electrophilic attack on an enol is the unstable epimer (kinetic control), which rearranges under acidic conditions into the more stable epimer or may even undergo positional isomerisation under thermodynamic control (see p. 385). Only under experimental conditions which inhibit subsequent rearrangements is it possible to be sure of isolating the primary product. In recent years the products of kinetically-controlled bromination have been obtained by permitting the enol acetate of the ketone to react with bromine in a buffered solution. Few free ketones are brominated at a useful rate under such mild conditions,... 

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