Butene second-order rate constants

Using haemoglobin and epoxybutene, Osterman-Golkar et al. (1991) observed the formation of two diastereomeric pairs of adducts to the N-terminal valine of haemoglobin namely V-(2-hydroxy-3-buten-l-yl) valine and V-( I -hydroxy-3 -buten-2-yl)valine. These findings were corroborated by Richardson et al. (1996), who incubated erythrocyte suspensions obtained from mice, rats and humans with epoxybutene. The second-order rate constant of adduct formation for the sum of both adducts (HOBVal) was determined in vitro at 37°C to be 0.29 x 10- L/g globin/h with erythrocytes isolated from mice (Recio et al., 1992 value corrected by the same authors to the one quoted here, Osterman-Golkar et al., 1993). 

Non-activated double bonds, e.g. in the allylic disulfide 1 (Fig. 10.2) in which there are no substituents in conjugation with the double bond, require high initiator concentrations in order to achieve reasonable polymerisation rates. This indicates that competition between addition of initiator radicals (R = 2-cyanoisopropyl from AIBN) to the double bond of 1 and bimolecular side reactions (e.g. bimolecular initiator radical-initiator radical reactions outside the solvent cage with rate = 2A t[R ]2 where k, is the second-order rate constant) cannot be neglected. To quantify this effect, [R ] was evaluated using the quadratic Equation 10.5 describing the steady-state approximation for R (i.e. the balance between the radical production and reaction). In Equation 10.5, [M]0 is the initial monomer concentration, k is as in Equation 10.4 (and approximately equal to the value for the addition of the cyanoisopropyl radical to 1-butene) [3] and k, = 109 dm3 mol 1 s l / is assumed to be 0.5, which is typical for azo-initiators (Section 10.2). The value of 11, for the cyanoisopropyl radicals and 1 was estimated to be less than Rpr (Equation 10.3) by factors of 0.59, 0.79 and 0.96 at 50, 60 and 70°C, respectively, at the monomer and initiator concentrations used in benzene [5] ... 

Oxidation rate constant k, for gas-phase second order rate constants, koe for reaction with OH radical, k os with NOj radical and ko3 with O3 or as indicated, data at other temperatures see reference koH = 3.41 X 10 " cm molecule- s- at 300 1 K (relative rate method with reference 2-methyl-2-butene Perry et al. 1977 Atkinson et al. 1979)... 

Calculated second order rate constants for disappearance of 1-butene. ... 

The identical rate of substitution of non-prochiral cis-2-butene for the coordinated 5,5-tbn measured by the two methods indicates the absence of other reactions such as local proton exchange between eis-2-butene and trows-2-butene. The second order rate constants for the tbn substitution measured by the two methods (kiso and kcd) are correlated with the rate constants for retent-... 

Table IV. Second Order Rate Constants and Activation Parameters for the Substitution of trans-2-butene for [PtCl3 (S,S-trans-2-bxitene [3 ]) ]- in Acetone (13)...

The direct reaction is first-order in the concentrations of the metal complex and the olefin and the second-order rate constant depends on the nature of olefin, as indicated by some of the data in Table S.9. Strain in the olefin appears to increase its reactivity, as shown for norbomene and cyclopentene. There may be some steric effects of olefin substituents, but these effects may be attenuated by better electron donation from the substituents. It was found also that the reaction rate with 2,3-dimethyl-2-butene was insensitive to the polarity of the solvent, with relative values of 1 0.6 0.8 in cyclohexane. Tiff and methanol, respectively. This seems to rule out an ionic or polar transition state or intermediate, and the authors favor a concerted cycloaddition mechanism. 

For 1-butene pyrolysis, the calculated first-order rate constants decreased significantly with increasing conversion at each temperature. Reduction of the data by using the integrated form of the second-order rate law provided specific rate constants that were satisfactorily independent of conversion. 

Epoxidation appears to involve electrophilic addition to the alkene, since the reaction is favored by electron-withdrawing groups on the peracid and electron-donating groups on the alkene. The epoxidation reaction is highly exothermic, with an experimental heat of reaction of -38 kcal/mol. The kinetic expression is overall second order, first order in the alkene and first order in the peracid. Steric effects do not appear to be important. The rate constant for the reaction increases with the number of alkyl substituents on the double bond, but the location of the alkyl groups is not important. For example, cis-2-butene, fra s-2-butene, and isobutene have nearly the same reactivity.The rate constant for the reaction is sensitive to strain, with faster rates observed for alkenes that produce greater relief of strain upon epoxidation. For example, frans-cyclooctene is epoxidized about 100 times faster than cis-cyclooctene. ... 

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