Temperature stopped-flow

It has long been known that substitution at the anion of Zeise s salt, [Pt(CH=CH2)Cl3], is, thanks to the high trans effect of the coordinated ethene, very fast. Recent developments in low-temperature stopped-flow apparatus have now permitted the study of the kinetics of substitution at Zeise s and other [Pt(alkene)Cl3] anions in methanol solution. These substitutions obey the customary two-term rate law (i.e. with kohs = ki+ /s3[nucleophile]), with large negative AS values for the k2 term as expected for Sn2 processes (196). 

D. S. Auld, K. Geoghegan, A. Galdes and B. L. Vallee, Biochemistry 25, 5156 (1986) C. Balny, T.-L. Saldana and N. Dahan, Anal. Biochem. 163, 309 (1987) describe a high-pressure, low temperature, stopped-flow apparatus. 

The formation of 2(NO) was too rapid to monitor by standard stopped-flow spectrophotometry, but the kinetics could be accessed using a low-temperature stopped-flow accessory. Second-order rate constants varied little in the range of —40 to —70 °C, but a significantly negative (—118 J/(mol K)) value of the entropy of activation was obtained. The reverse reaction, dissociation of NO, could be characterized kinetically, but some doubt was expressed about the accuracy of the parameters. Laser flash photolysis could be applied in the ambient temperature range and the value of AS for the forward reaction of Equation 7.48 was confirmed at... 

A detailed kinetic study has been carried out for the formation of 2 from 1 and O2. Figure 4 shows the kinetic scheme deduced from a low-temperature stopped-flow kinetic/spectroscopic study. The 1 1 intermediate [LCu(02)] species was detected at... 

Buck and Moore have extended their low-temperature stopped-flow studies on the formation and dissociation of complexes of Mn + to bipyridyl-type ligands in DMSO. The rate constants for bipy are log kf = 3.89 and log Ara [mercury(n)-induced dissociation] = 1.26 at 291.7 K. 

Fire Hazards - Flash Point Not pertinent Flammable Limits in Air (%) 1.6- 10 Fire Extinguishing Agents Stop flow of gas Fire Extinguishing Agents Not To Be Used Not pertinent Special Hazards of Combustion Products Not pertinent Behavior in Eire Containers may explode in fires. Vapor is heavier than air and may travel considerable distance to ignition source and flash back Ignition Temperature (deg. F) 725 Electrical Hazard Not pertinent Burning Rate No data. 

Figure 4-12. Stopped-flow study of the pyridine-catalyzed hydrolysis of acetic anhydride, showing the formation and decay of the acetylpyridinium ion intermediate. Initial concentrations were 0.087 M pyridine, 2.1 x im M acetic anhydride the pH was 5.5 ionic strength, 1.0 M temperature, 25 C. Five hundred data points tabsorbance at 280 nm) were measured in I s. The smooth curve is a ht to Eq. (3-27). Source Data of D. Khossravi and S.-F. Hsu, University of Wisconsin.

Kerosine is usually a clear colorless liquid which does not stop flowing except at very low temperature (normally below -30°C). However, kerosine containing high olefin and nitrogen contents may develop some color (pale yellow) after being produced. 

In the study of reactions of the types ether than exchange mentioned previously, the usual technique involves the spectrophotometric examination of reaction mixtures. The absorbance changes that occur, at a suitable wavelength where only one species (either reactant or product) absorbs, as the reaction proceeds are measured (manually or recorded). Treatment of the data via the Beer-Lambert law enables rate coefficients and laws to be found in the usual manner. Stopped flow and temperature jump techniques have been used for very rapid reactions. 

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