Olefins rate constants

Type of substitution Olefin Rate constant Coordination constant K(l/molf Specific rate at 1.0 mol/l-olefm ifcX10 (s f... 

If aryl azides are irradiated in acidic medium in the presence of arenes, derivatives of diphenylamine are formed." For the diphenylnitrenium ion, G-complexes with benzene have been detected by laser flash photolysis. In reactions with alkenes, nitrenium ions react more rapidly with electron-deficient olefins. Rate constants for the reaction of diphenylnitrenium with electron-rich olefins such as cyclohexanone trimethylsilyl enol ether are of the order of 1.9 x 10 M" s". In the reaction of 2-fluorenylni-trenium with 2 -deoxyguanosine, reaction at C8 of the guanine base takes place. ... 

Butylene isomers also can be expected to show significant differences in reaction rates for metaHation reactions such as hydroboration and hydroformylation (addition of HCo(CO). For example, the rate of addition of di(j -isoamyl)borane to cis-2-huX.en.e is about six times that for addition to trans-2-huX.en.e (15). For hydroformylation of typical 1-olefins, 2-olefins, and 2-methyl-l-olefins, specific rate constants are in the ratio 100 31 1, respectively. 

Many researchers have correlated the overall decomposition as an nxh. order reaction, with most paraffins following the first order and most olefins following a higher order. In general, isoparaffin rate constants are lower than normal paraffin rate constants. The rate constants are somewhat dependent on conversion due to inhibition effects that is, the rate constant often decreases with increasing conversion, and the order of conversion is not affected. This has been explained by considering the formation of aHyl radicals (38). To predict the product distribution, yields are often correlated as a function of conversion or other severity parameters (39). 

FIG. 18 The effect of chain length on the pseudo rate constants (Km (100 90)) of n-hexadecane solubilization by olefinsulfonates/dobanol 45-3 solutions at 40°C. AOS, a-olefinsulfonate IOS a, aged I-olefinsulfonate IOS d, directly hydrolyzed I-olefin-sulfonate. 

The observation (Porter ef a ., 1972) that added BrCCla almost completely suppresses the polarization of the olefin, while leaving the polarization of trans-4 unalfected, points to the secondary radical pair as the principal immediate precursor of a-methylstyrene. A rate constant for the decomposition of thediazenyl radical of 10 -10 sec has been estimated. Cage collapse and free-radical formation are also thought to occur and appropriately polarized products have been identified (see above). 

If return occurs during the bromination of cw-stilbenes and rotation around the C-C bond is faster than collapse of the intermediates to dibromides, this process will lead to fra j-stilbene (Scheme 9). We used this test to check the possibility of return in the bromination of unsubstimted, 4-methyl, 4-trifluoromethyl-, and 4,4 -bis(trifluoromethyl)-stilbenes in DCE (ref. 24). All these olefins gave clean third-order rate constants spanning 7 powers of 10. For each cis-trans couple the cis olefin was brominated 3.5 to 5.5 times faster than the trans isomer. Reactions for products analysis were performed at initial molar ratios of Br2 to olefin of 1 to 2, so that products arose only from the cis olefin, the trans isomer being accumulated in the reaction medium. 

Relative Second-Order Rate Constants for Ozonations of Selected Olefins in CCI4 at Room Temperature... 

Due to their weak P-H bonds (-370 kj mol"0 [2] and the high rate constants for the transfer of the P-H hydrogen [3] (/c=1.5 10 L rnoL s" for Ph2PH and k=5,0 10 L mol s for (c-hexyl)2PH), diaryl and dialkyl phosphines present a high interest as H-donors. Since the corresponding phosphinyl radicals are good chain carriers [4,5], diaryl and dialkyl phosphines can be added to olefinic or acetylenic compounds through radical chain reactions. Simpkins et al. [6] used... 

Tl(III) < Pb(IV), and this conclusion has been confirmed recently with reference to the oxythallation of olefins 124) and the cleavage of cyclopropanes 127). It is also predictable that oxidations of unsaturated systems by Tl(III) will exhibit characteristics commonly associated with analogous oxidations by Hg(II) and Pb(IV). There is, however, one important difference between Pb(IV) and Tl(III) redox reactions, namely that in the latter case reduction of the metal ion is believed to proceed only by a direct two-electron transfer mechanism (70). Thallium(II) has been detected by y-irradiation 10), pulse radiolysis 17, 107), and flash photolysis 144a) studies, butis completely unstable with respect to Tl(III) and T1(I) the rate constant for the process 2T1(II) Tl(III) + T1(I), 2.3 x 10 liter mole sec , is in fact close to diffusion control of the reaction 17). 

Other substituted olefins such as acrylonitrile, fumaronitrile, crotono-nitrile, cinnamonitrile, and diethylfumarate also formed adducts with Co (DMG)2 complexes containing py, H2O, or PBuj and, in one case, with [Co (DMG-BF2)2py]. Second-order rate constants were reported for the formation of several Tr-olefin-Co(I) complexes from organocobalt(III) complexes containing, for example, NCCH2CH2- with DMG, DPG, DMG-BF, py, H2O, and PBuj. 

In order to rationalize such characteristic kinetic behaviour of the topochemical photoreaction, a reaction model has been proposed for constant photoirradiation conditions (Hasegawa and Shiba, 1982). In such conditions the reaction rate is assumed to be dependent solely on the thermal motion of the molecules and to be determined by the potential deviation of two olefin bonds from the optimal positions for the reaction. The distribution of the potential deviation of two olefin bonds from the most stable positions in the crystal at OK is assumed to follow a normal distribution. The reaction probability, which is assumed to be proportional to the rate constant, of a unidimensional model is illustrated as the area under the curve for temperature Tj between 8 and S -I- W in Fig. 7. 

This type of reaction is involved as an intermediate step in few synthetically useful reactions, in the formation of polysulfones by copolymerization of an olefin with SO 2, as well as in aerosol formation in polluted atmospheres. We will discuss later in some detail the most important chain reactions involving step 11. However, Good and Thynne determined the Arrhenius parameters for the addition of methyl and ethyl radicals to SO2 in gas phase, the rate constants being 5 x 10 and 4 x 10 s respectively at ambient... 

By analogy to simple olefins, we propose that 0(3P) initially adds to the 1,4 or 1,2 double bonds in polybutadienes at ambient temperature. Since the rate constants for 0(3P) addition to cis-2-butene and 1-butene (as models for 1,4 and 1,2 double bonds, respectively) are in the ratio 4.2 1 at 298 K ( 6), preferential addition to the 1,4 double bonds is assumed to persist to very high vinyl contents (-8011). The biradical adducts then rearrange to epoxides and carbonyl compounds or give rise to chain rupture and/or crosslinking as a consequence of PIF, according to the scheme ... 

The quantum yield for the formation of the cycloaddition product has been found to be temperature dependent, increasing by a factor of approximately three as the temperature is lowered from 65 ( = 0.24) to 5°C ( = 0.69). Photolysis of mixtures of the olefin and f/my-stilbene in the presence of sensitizers yielded no cycloaddition product (42) but rather only m-stilbene. This suggests that the cycloadduct is produced via a singlet reaction. This conclusion is supported by the fact that tetramethylethylene quenches fluorescence from the /rans-stilbene singlet. A plot of l/ (42) vs. 1/[TME] (TME = tetramethylethylene) is linear. The slope of this plot yields rate constants for cycloadduct formation which show a negative temperature dependence. To account for this fact, a reversibly formed exciplex leading to (42) was proposed in the following mechanism<82) ... 

Bromination data became accessible over a large reactivity range when it became possible to follow low bromine concentrations. All the modern kinetic techniques are based on the fact that, since bromination is a second- or third-order reaction, bromination half-lives of a few milliseconds to several seconds can be obtained by working at very low reagent concentrations. For example, second-order rate constants as high as 109 m 1 s 1 can be readily measured if the reagent concentrations are 10-9m, the half-life of the bromine-olefin mixture then being 1 s. 

The quantum yields for oxetane formation have not been determined in every case, and only a few relative rate constants are known. The reactivities of singlet and triplet states of alkyl ketones are very nearly equal in attack on electron rich olefins. 72> However, acetone singlets are about an order of magnitude more reactive in nucleophilic attack on electron-deficient olefins. 61 > Oxetane formation is competitive with a-cleavage, hydrogen abstraction and energy-transfer reactions 60 64> so the absolute rates must be reasonably high. Aryl aldehydes and ketones add to olefins with lower quantum yields, 66> and 3n-n states are particularly unreactive. 76>... 

Surface water t,/2 = 320 h and 9 x 104 d for reaction with OH and R02 radicals of olefins in aquatic system, and t,/ = 7.3 d, based on oxidation reaction rate constant k = 3 x 103 M 1 s 1 with singlet 02 for unsubstituted olefins in aquatic system (Mill Mabey 1985). 

---