Alkyl radical additions to double and triple bonds

16 ALKYL RADICAL ADDITIONS TO DOUBLE AND TRIPLE BONDS 

The literature on the reactions of alkyl radicals is voluminous. A number of pioneers in free radical chemistry (Steacie, for example) worked on reactions of the small alkyl radicals, and trained numerous students who continued in the field. A second input of data came from the interest in free radical polymerization, and the two topics have interacted in the area of kinetics. Undoubtedly, the experimental problems of generation, measurement and determination of the fate of alkyl radicals provided a challenge to many workers, which has manifested itself 

The present discussion is by no means exhaustive. It is designed to provide a summary of the most significant and reliable kinetic data, at least those that appear so to the author. There is a variety of methods for producing alkyl radicals, and, naturally, there will be certain restrictions on experimental conditions depending on the method chosen. Some of the common methods for generation of methyl radicals, for example, include photolysis of acetone, pyrolysis of di-ferf-butyl peroxide, photolysis of biacetyl, photolysis of azomethane and decarbonylation of acetaldehyde. In the majority of cases discussed here, the reactions were followed by product determinations, employing gas chromatography. 

The results for the addition of methyl radicals to ethylene are presented in Table 47. Kerr and Parsonage [1] have plotted the results of the various workers [160—163] to obtain the most reliable Arrhenius parameters, and their preferred rate equation for this reaction is log k = 8.52— 7700/2.3IJT. 

Coming to the reaction of methyl radicals with propene, there are two sites for attack, producing secondary butyl or isobutyl radicals. Miyoshi and Brinton [164] analysed their products and estimated that about 90% of the attack is on the terminal carbon. The reported rate coefficients in Table 48 are composites of terminal and non-terminal attack, but the relatively small amount of the latter means the rates are very close to those for addition to the terminal carbon atom. In this case also, Kerr and 

---