Naphthalene regioselective isopropylation

Dealumination of HM resulted in common features for both the isopropylation of biphenyl and naphthalene. The dealumination of HM decreases the blocking of the pores by coke deposition in the both reactions because of the decrease in acid sites at intracrystalline and external surfaces. It also reduced the non-regioselective isopropylation at the external surface, and enhanced the reaction to yield the least bulky product molecules. The pressure of propylene is also an important key factor for high yield of 4,4 -DIPB in the isopropylation of biphenyl, because the isomerization of 4,4 -DIPB occurred significantly under low pressure of propylene at the external acid sites. 

Olah has found perfluoroalkanesulfonic acids, such as perfluorodecanesulfonic acid (PDSA, C10F21SO3H), to be very effective catalysts for regioselective isopropylation of naphthalene (equation 27). 

The product distribution in the zeolite-catalysed alkylation of polynuclear aromatics depends on the structure of zeolite pores. High regioselectivities were observed in the HM catalysed isopropylation of polynuclear aromatics, such as biphenyl, naphthalene, p-terphenyl, and dibenzofuran, to yield predominantly the least bulky products e.g., 4,4 -DIPB for biphenyl, and 2,6-DIPN for naphthalene. These reactions are controlled by steric restriction at the transition state inside the pores and by the entrance of intermediate products molecules into the pores. On the other hand, the catalysts with large-pore HY and HL zeolite are controlled at low temperature by the electron density of the reactant molecule and at higher temperature by the stability of the product molecules because their pores have enough space for a transition state, which allow the formation of all corresponding isomers. 

Song, C. and A. Schmitz. Shape-Selective Isopropylation of Naphthalene over Dealuminated Mordenite. Key Factors Affecting Regioselectivity. Extended Abstracts, Program. 11th Internat. Congress on Catalysis, Baltimore, Maryland, June 30-July 5, 1996, Po-164. 

Schmitz and Song investigated the reactivity of 2,6-DIPN over HM under propylene pressure. Over HM(14) and HM(38), 2,6-DIPN conversions were 12-27% mostly to higher alkylates. The isopropylation of 2,6-DIPN increased over these HM under high propylene pressures, but its isomerization was suppressed. Both reactions of 2,6-DIPN produce a-substituted naphthalenes by non-regioselective reactions on the external surface. On the other hand, 2,6-DIPN was nearly unreactive over HM(74) because of fewer external acid sites compared with HM(14) and HM(38). These results reveal that high selectivity toward 2,6-DIPN in the isopropylation of naphthalene is partly ascribed to the low reactivity of 2,6-DIPN. 

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