Isopropoxy radical

Dialkyl peroxydicarbonates have been reported as low temperature sources of alkoxy radicals (Scheme 3.30)lfMJfb and these radicals may be formed in relatively inert media. However, it is established, for primary and secondary peroxydicarbonates, that the rate of loss of carbon dioxide is slow compared to the rate of addition to most monomers or reaction with other substrates.186,187 Thus, in polymerizations carried out with diisopropyl peroxydicarbonate (47), chains will be initiated by isopropoxycarbonyloxy (48) rather than isopropoxy radicals (49) (see 3.4.2.2).188... 

The alkoxycarbonyloxy radicals show little tendency to abstract hydrogen.188,431 For example, in the reaction of isopropoxycarbonyloxy radicals with MMA, hydrogen abstraction, while observed, is a minor pathway (<1%). When isopropoxycarbonyloxy radicals abstract hydrogen, isopropanol is the expected byproduct since the intermediate acid undergoes facile decarboxylation. Formation of isopropanol is not evidence for the involvement of isopropoxy radicals (Scheme 3.80). 

Thus, although the reaction R +NO is very efficient, NO is not in fact a good radical trap, because of the complicating reactions due to the instability of the products, except possibly at the lower temperatures of 100-200° C. Thus, Phillips et have used NO in the study of the pressure-dependent decomposition of the isopropoxy radical. There are some similarities with the reactions of O, such as R--(-02 ROj- and O2-I-RH -> H02- + R-. Here, inhibition takes the special form of oxidation. 

Here (CH3)2CHO in primary process (II) represents a vibrationally excited isopropoxy radical that can decompose quickly to products. Process (IV) is probably an unimportant photodecomposition mode within the troposphere. The mechanism and extent of these processes will be discussed in this section. 

Ludwig, B.E., and GR. McMillan (1967), Disproportionation and combination reactions of isopropoxy radicals with nitric oxide, J. Phys. Chem., 71, 762-764. 

Relatively few studies have dealt with the reactions of primary and secondary aikoxy radicals (isopropoxy, methoxy, etc.) with monomers. These radicals are conveniently generated from the corresponding hyponitrites (Scheme 3.77).1"3 402... 

It is evident that the tendency for free radical polymerization is a function of the monomer. Natta (287) stated that these radicals can initiate polymerization of styrene and diolefins to high molecular weight products but not that of aliphatic alpha olefins. North (339) showed that the decomposition of phenyl tri-isopropoxy titanium initiates radical polymerization of styrene but not of ethylene. 

The methoxides and ethoxides of lanthanoids are insoluble solids. The derivatives of phenols and higher alcohols are amorphous or crystalline substances soluble in common organic solvents. Some of them (isopropoxides, tert-butoxides and derivatives of 2,6-di-tert-butylphenols) are sublimed in vacuum at 190-250 C. The cerium tetra-alkoxides with tertiary-radicals appear to be distillable liquids. The mixed alkoxide of lanthanum La(0C3H7-i)2(0CH2C4H70) containing the residue of tetrahydrofurfuryl alcohol OCH2C4H7O and the isopropoxy groups remains liquid at room temperature [14]. 

Adam, W., Marquardt, S., and Saha-Moller, C.R., Oxidative DNA damage in the photolysis of N-hydroxy-2-pyridone, a specific hydroxyl-radical source, Photochem. Photobiol, 70, 287-291, 1999. Adam, W., Hartung, J., Okamoto, H., Marquardt, S., Nau, W.M., Pischel, U., Saha-MoUer, C.R., and Spehar, K., Photochemistry of N-isopropoxy-substituted 2(lEf)-pyridone and 4-p-tolylthiaz-ole-2(3H)-thione alkoxyl-radical release (spin-trapping, EPR and transient spectroscopy) and its significance in the photooxidative induction of DNA strand breaks, /. Org. Chem., 67, 6041-6049, 2002. 

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