Highly Selective Synthesis of Polyalkylated Naphthalenes Catalyzed by Ionic Liquids and Their Tribological Properties as Lubricant Base Oil

Abstract Naphthalene, one of the most important components in coal tar, is now in serious surplus. The Ionic Liquids (ILs) of Et 3 NHCl‐AlCl 3 were used as Lewis acidic catalysts for an alkylation reaction of naphthalene with medium‐chain alfa‐olefin ( n ‐hexene/ n ‐octene) to produce a lubricating base oil. Polyalkylated naphthalenes consisting of tri‐ and tetra‐alkylnaphthalenes can be obtained with a selectivity as high as 98% under mild conditions. We propose a plausible mechanism for the alkylation process catalyzed by Lewis acidic AlCl 3 derived from the dissociation of [Al 2 Cl 7 ] − anion in ILs. The physicochemical properties and tribological performances of synthesized polyalkylated naphthalenes, and especially poly‐octylnaphthalenes, are found to exhibit the properties of lubricating base oils, and are comparable to those of the conventional cycloalkyl base oil.