A-Acetoxyethyl radicals

Hie Rate of Addition of Vinyl IVIonomers to a-Acetoxyethyl Radicals... 

Ranby et al. used the photolytically-generating flow method to measure the addition rates of vinyl monomers. They found that the a-acetoxyethyl radical, a model of... 

Fig. 38. ESR spectrum for 0.3 M DTB photolyzed in ethyl acetate at 27 C. Spectrum consists of a quartet of doublets of quartets, and can be assigned to a-acetoxyethyl radical. Second order splittings can be seen for the lines corresponding to the inner two components of the larger quartet...

New radicals appearing in the spectrum upon addition of a monomer are assignable to addition radicals formed by the attack of the a-acetoxyethyl radical, They are only the monomer addition radicals with the acetoxyethyl group, though the monomer concentration used is considerably higher than those in the kinetic experiments described below. Thus, the propagation of the monomer radical will be neglected in the subsequent kinetic considerations. 

Figures 39 a and b show changes in a-acetoxyethyl radical concentration with the concentration of the added monomer. From the slopes of the dashed lines together with the estimated values of (2k [R ]o)> Ih following values were obtained for k at 25 °C k == 1.1 x 10 s" for acrylonitrile, 9.4x10 s for methyl...

Direct evidence for the formation of a radical cation 12 on cleavage of a radio-lytically generated a,a-dimethoxy-j8-acetoxyethyl radical 11 was obtained by Schulte-Frohlinde and coworkers by ESR spectroscopy (Scheme 5) [12]. 

Benzyne is a necessary intermediate in the diazotization of 2-[(2-acetoxyethyl)sulfinyl(and sulfonyl)]anilines 107 and 116, but a detailed study of the way it is formed gave some surprises . Products from the aprotic diazotization of 107 included biphenylene 67 and dibenzo-l,4-thioxin 112. EPR evidence for radical intermediates was obtained. Formation of 112 requires cleavage of the S—O bond, most probably via benzoxathiete 110 as shown. Although yields of 67 and 112 were low, when the diazotization was carried out in the presence of benzyne traps such as diphenylisobenzofuran or anthracene, respectable yields (30-40%) of the corresponding benzyne cycloadducts were obtained. 

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