Ethylation and Transethylation of Naphthalene

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Transethylation of naphthalene by ethylxylenes and ethylbenzene in the presence of AlCl3 as a catalyst was studied and compared with ethylation by ethyl bromide. When ethylxylenes were used, it was observed that the β-isomer of ethylnaphthalene initially formed (96.8%) was isomerized to the α-isomer. This was attributed to steric hindrance of the α-position in the transition state of reactions proceeding by the hydride abstraction mechanism. However, the formation of considerable proportion of the α-isomer (25%) was observed in the case of transethylation by ethylbenzene, as well as of ethylation with ethyl bromide (60% α-isomer). Thus, the SN2 mechanism should be operative, at least partly, in the transethylation by ethylbenzene. The rates of transethylation by ethylxylenes were found to be in the order: 1,2-diMe-4-Et-\overset·\underset·≈1,3-diMe-4-Et->1,4-diMe-2-Et->>1,3-diMe-5-5-Et-benzene. The equilibrium composition of ethylnaphthalene was found to contain 8.7–8.8% α-isomer.
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