摘要：

The gallium bromide-catalyzed reactions of ethyl bromide with the halobenzenes have been examined in ethylene dichloride solution at 25°. Using a competitive method, the rate of ethylation of fluorobenzene relative to benzene has been determined as 0.282. Under these conditions the isomeric fluoroethylbenzenes are formed in the proportion: 42.9% p-, 13.7% m- and 43.4% p-fluoroethylbenzene. These data provide the partial rate factors ofF 0.364, mfF 0.116 and pfF 0.738. In the ethylation of chlorobenzene, the rate ratio is 0.214, and the isomer distribution is 42.2% o-, 15.9% m- and 41.9% p-chloroethylbenzene. These results yield the partial rate factors for the ethylation of chlorobenzene ofCl 0.271, mfCl 0.102 and pfCl 0.538. In the case of bromobenzene, the relative rate was determined to be 0.133 and the product ratio evaluated as 24.0% o-, 21.8% m- and 54.2% p-bromoethylbenzene. These observations provide the partial rate factors ofBr 0.096, mfBr 0.087 and pfBr 0.433. Under conditions suitable for the ethylation of the other halobenzenes, iodobenzene-benzene reaction mixtures failed to yield ethylation products. The partial rate factors for ethylation reveal the halobenzenes are deactivated in all nuclear positions, least in the para position. The observation that pfF is less than unity contrasts with the results for t-cumyl chloride solvolysis and for the mercuration reaction. The available data for the gallium bromide-catalyzed ethylation of monosubstituted benzene are assembled and examined. With the exception of the partial rate factor for p-fluoro, these rate data are correlated by the electrophilic substituent constants, σ+, based upon t-cumyl chloride solvolyses.

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