Kinetics MIMS

Missen, R. W., Mims, C. A., and Saville, B. A., Introduction to Chemical Reaction Engineering and Kinetics, John Wiley Sons, 1999. 

Mayo-Lewis Binary Copolymeriration Model. In this exeimple we consider the Mayo-Lewis model for describing binary copolymerization. The procedure for estimating the kinetic parameters expressed as reactivity ratios from composition data is discussed in detail in our earlier paper (1 ). Here diad fractions, which are the relative numbers of MjMj, MiMj, M Mj and MjMj sequences as measured by NMR are used. NMR, while extremely useful, cannot distinguish between MiM and M Mi sequences and... 

For iron(III) eomplexes, uic venues /vlh [Fe(aepa)2]BPh4 H2O and k = 6.7 x 10 s for [Fe(mim)2(salacen)]PF6 have been obtained [156, 166]. The rate constants derived from the line shape analysis of Mossbauer spectra thus vary between 2.1 x 10 and 2.3 x 10 s at room temperature, no significant difference between iron(II) and iron(III) being apparent. In addition, it is evident that the rates of spin-state conversion in solution and in the crystalline solid are almost the same. For iron(II) eomplexes, for example, the solution rates vary between /cjjl = 5 x 10 and 2 x 10 s , whereas in solid compounds values between kjjL = 6.6 x 10 and 2.3 x 10 s have been obtained. Rates resulting from the relaxation of thermally quenched spin transition systems are considerably slower, since they have been measured only over a small range of relatively low temperatures. Extrapolation of the kinetic data to room temperature is, however, of uncertain validity. 

CHARLES A. MIMS is a Professor of Chemical Engineering and Applied Chemistry at the University of Toronto. He earned his B.Sc. in chemistry at the university of Texas, Austin, and his Ph.D. in physical chemistry at the University of California, Berkeley. He has 15 years of industrial research experience at Exxon, is the author of over 65 research publications, and holds three patents. His research interests focus on catalytic kinetics in various energy and hydrocarbon resource conversion reactions, and the fundamentals of surface reactions. 

Chemical reactors. 2. Chemical kinetics. I. Mims, Charles A. 

August , R., Dias, A.O., Rocha, L.L., and Lago, R.M. Kinetics and mechanism of benzene derivative degradation with Fenton s reagent in aqueous medium studied by MIMS, / PA/s. Chem. A, 102(52) 10723-10727, 1998. 

MIMS is a technique that uses a semipermeable membrane for directly introducing analytes into the mass spectrometer. This allows analytes to be measured in realtime with little or no sample preparation. MIMS has been previously used to measure the stability of CNCl in chlorinated and chloraminated drinking water [168], to quantify CNCl and CNBr in drinking water [169], to measure chloramines and chlorobenzenes in water samples [170], and investigate the mechanism and kinetics of chloroform formation in drinking water [171]. More recently, it has been used to measure volatile DBPs in indoor swimming pools [138, 172]. 

The use of membrane introduction mass spectrometry (MIMS) was first reported in 1963 by Hoch and Kok for measuring oxygen and carbon dioxide in the kinetic studies of photosynthesis [46], The membrane module used in this work was a flat membrane fitted on the tip of a probe and was operated in the MIS mode. The permeated anaytes were drawn by the vacuum in the MS through a long transfer line. Similar devices were later used for the analysis of organic compounds in blood [47], Memory effects and poor reproducibility plagued these earlier systems. In 1974, the use of hollow-fiber membranes in MIMS was reported, which was also operated in the MIS mode [48], Lower detection limits were achieved thanks to the larger surface area provided by hollow fibers. However, memory effects caused by analyte condensation on the wall of the vacuum transfer line remained a problem. 

Missen RW, Mims CA and Saville BA, "Introduction to Chemical Reaction Engineering and Kinetics", Wiley, New York, 1999. 

By moving from kinetically controlled to thermodynamically controlled reactions (Fig. 27), MIMs can now be synthesized in near-quantitative yields, primarily... 

Ligand substitution is thus kinetically faster than antissfe gauche isomerization. Another example of kinetic control in ligand substitution at a dimolybdenum center is seen in the following. Hexane solutions of 1 -MogBrglCHgSiMe (MiM) react... 

Kinetic and thermodynamic studies of geranyl acetate production by direct geraniol acetylation with lyophilized cells of A. oryzae MIM were carried out in n-heptane [13-15]. Batch tests were performed varying the starting substrates equimolar level from 25 to 150 mM, cell concentration from 5 to 30g/l, and temperature from 30 to 95 °C. The initial rates at different initial substrate concentrations were measured and an apparent Michaelis constant KJ of 62mM and a fee value of 0.88 mmol/g/h were estimated by direct fitting of the initial rates against the initial substrate concentrations <75 mM [15]. 

A very different situation was observed when the resolution of racemic 1,2-0-isopropyhdeneglycerol (IPG or solketal) was studied [19]. In this case, the kinetics of the esterification with butyric acid catalyzed by A. oryzae MIM and R. oryzae CBS 112.07 were investigated by carrying out independent batch tests on the commercially available R- and S-IPG (Table 6.4). 

Table 6.4 Kinetic parameters of R- and S-IPG esterification with butyric acid catalyzed by R. oryzae CBS 112.07 and A. oryzae MIM.

In the hydrolysis of NABA 6 catalyzed by MIm-VP copofymers, the reaction rate saturated at higher substrate concentrations (> O.OS M) and the rate data conformed to the Michaelis-Menten kinetics. The and values (9—11 mM and... 

Kunitake and Okahata examined the hydrolysis of PNPA in the presence of vinyl polymers containing N-phenylhydroxamate (PHA) and methylimidazole(MIm) units (107). The reacticm of PHA-MIm-AAm tetpolymer 23 with large excesses of PNPA gives typical burst kinetics initial rapid liberation of p-nitrophenol (k ) followed by slower, steady release (ktt). 

The above consideration does not purport to be full. We did not even mention here very powerful methods providing extremely valuable kinetic information, such as various spectroscopies (especially performed in in situ mode) and isotope tracing and labeling. Although these methods substantially improve the efficiency of model validation and elucidation of reaction pathways (see, for instance Mims et al., 1994), they have not yet become very common in kinetic experimentation for kinetic modeling . Instead, we focused on some problems typical for everyday practice and just traced possible solutions. 

Missen, R.W., Mims, C.A., SavUle, B. A., 1999. Introduction to chemical reaction engineering and kinetics. John WUey Sons, New York. 

For analytes having half-lives shorter than 30 min in the sample solution, the delay of MIMS response due to mass transfer must be accounted for to convert MS ion counts to concentration. This is particularly important for measuring disinfectant or DBF concentrations because unless disinfectants are quenched, there is almost certain to be reactions between disinfectants and natural organic matter (NOM) always present in natural water (i.e., DBF formation) [20] or reactions between disinfectants and DBFs (i.e., DBF decay). Another situation requiring consideration of MIMS response times is when relatively fast reaction kinetics is of interest [17],... 

MIMS has been applied to analyzing disinfectants and DBFs in three different ways. The applications of MIMS include (1) understanding the speciation of chlorine-based disinfectants, (2) identifying and quantifying DBFs, and (3) elucidating the mechanisms of DBF formation and stability through kinetic measurements. The first two applications can be performed following the procedures outlined in Section 27.2.3.The third application may involve the employment of the protocols outlined in Section 27.2.4. 

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