A Study on the Complex Layer of Alkylbenzene-AlCl3-HCl System during Transalkylation -Diethylbenzene AlCl₃- HCl System-

Abstract

The complex layers obtained by the reactions of p-diethylbenzene(p-DEB) and m-diethylbenzene(m-DEB) with the AlCl₃-HCl system were investigated by using ¹³C-NMR in order to elucidate the mechanism of transalkylation of alkylbenzenes. m-DEB was readily protonated to give its benzenium ion (Fig.2(a)), but p-DEB was rapidly transalkylated into ethylbenzene and 1, 2, 4-triethylbenzene, the latter being further converted to 1, 3, 5-triethylbenzene(s-TEB)which in turn was protonated to give its very stable benzenium ion (Table 1 and Fig.1).
The transalkylation appeared to consist generally of successive dealkylation and alky lation and that the dealkylation occurs at the position of the ring carbon having the higher electron density, since the protonation of the ring carbon was the first step of this reaction. Therefore, the different behavior between p-DEB and m-DEB was explained by comparison of the 13C chemical shifts of their ring carbons which were in parallel with the electron density (Fig.5).
Namely, the stability of protonated ethylbenzenes decreased in the order m-DEB s-TEB >ethylbenzene>l, 2, 4-triethylbenzene>p-DEB, whereas their reactivity gave the opposite sequence, as observed in the reaction carried out by adding successively AlCl₃- and HCl to the diethylbenzene mixture (Table 3 and Fig.3). These results showed that the transalkylation of diethylbenzenes might occur according to the reaction courses given in Fig.6