Activation energy allyl esters

The thermal racemization of optically active aryl allyl sulfoxides ArS(0)CHjCH=CH2 is orders of magnitude faster, and has a much lower activation energy, than that of aryl alkyl sulfoxides ArS(0)R (Bickart et ai, 1968). The reason is that the presence of the allyl group permits the sulfoxide to equilibrate with the isomeric, achiral sulfenate ester by a concerted, cyclic process (89) for whichis only about 20 kcal moM.The rates of racemiz-... 

Kinetic results are given in Table 9. The toluene carrier technique often yields low values of the activation energies and 4-factors. Results for the benzyl esters, however, appear to be reasonably good. Note that the estimated reaction enthalpies compare favorably with the observed activation energies and that -factors are reasonable (AS 5 cal.deg mole ). Since only absolute decomposition rate coefficients were reported for the allyl esters, we have estimated the Arrhenius parameters on the assumption that the -factors were all 10 sec The activation energies so obtained are reasonable, since they compare quite favorably to those estimated by group additivities and the accepted heats of formation of the product radicals (Column 3, Table 9). 

This is about 9 kcal.mole" higher than the ethyl acetate elimination activation energy, but is nevertheless reasonable since the vinyl (C-H) bond which is broken in the allyl ester reaction is close to 15 kcal.mole stronger than the sp (C-H)bond in ethyl acetate. 

Gas phase kinetic data have been reported for only two of these reaction subclasses, allyl esters (2), and vinyl allyl ethers (4). Subclasses (5), (6) and (1) have very fast reverse processes (see activation energy predictions), but could be observed in terms of loss of optical activity at the 4-position. It would be interesting to look for these reactions. 

A kinetics study of the maleinisation of alkyl esters of high-oleic sunflower oil indicated that the maleinisation reaction was of second order overall and first order with respect to the individual reactants. The activation energy was 77.2-63.3 kJ mol in the investigated temperature range (185-225 C). It is also clear that there are two different and independent reaction mechanisms, an ene-reaction and addition in the allylic position with a 2 1 ratio respectively involved in this esterification reaction (Fig 4.5). ... 

With purified resin, alcohol decreases the interphase tension, with the exception of OP-10 (allyl phenol oxyethylated ester) for which it produces some increase (by ImN/m) [12]. These findings can be explained by the fact that the alcohol facilitates desorption of the low-molecular weight resin fractions with surface-active properties from the boundary between the resin and the mercmy by increasing their compatibility with the bulk resin. The free energy advantage for alcohol adsorption on the mercury surface is less than that for low-molecular weight fractions, which is why it results in increase of the interphase tension. 

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