Synthesis of 2-Isopropyl Naphthalene Catalyzed by Et3NHCl-AlCl3 Ionic Liquids

March 30, 2014

China Petroleum Processing and Petrochemical Technology

2014, V ol. 16, No. 1, pp 60-65

Catalyst Research

Recieved date: 2013-08-20; Accepted date: 2013-10-31.Corresponding Author: Tang Xiangyang, E-mail: txy@.

1　Introduction

2-Isopropyl naphthalene is an important raw material in chemical industry and it is a most important starting chemical for producing 2-naphthol which is mainly used for the production of organic pigments and dyes interme-diates, rubber antioxidant, bactericide, mildew preserva -tives and other chemicals [1-2]. As naphthalene is active at a relatively high temperature, alkylation reaction of naph-thalene is prone to generate multi-alkylated products and the yield of mono-alkylated product is low. In addition, it is difficult to separate the products with alkyl groups at the 1-position and 2-position of naphthalene molecules

[3-6]

.

The current production process is faced with some chal-lenges such as environmental hazard, non-reusability of catalyst, difficulties in recycling and disposal of the spent catalysts as well as product separation and purification. Therefore, great efforts have been directed to the develop-ment of a facile and environmental friendly catalytic route to improve the reactants conversion and the selectivity of 2-isopropyl naphthalene [7-11].

Among so many catalytic processes studied extensively on ionic liquids, the alkylation reactions have received increasing attention due to their potential application in

Synthesis of 2-Isopropyl Naphthalene Catalyzed by

Et 3NHCl-AlCl 3 Ionic Liquids

Li Chenmin; Qi Xin; Tang Xiangyang

(Department of Chemistry, Tianjin University, Tianjin 300072)

Abstract: In this paper, 2-isopropyl naphthalene has been synthesized by the reaction of naphthalene and isopropyl bromide, using triethylamine hydrochloride-aluminum chloride ionic liquid as the catalyst. The effect of the catalyst composition, the reaction time, the reaction temperature, the ionic liquid dosage, as well as the molar ratio of the reagents on the 2-isopropyl naphthalene yield was systematically investigated. The optimal reaction conditions cover: an AlCl 3 to Et 3NHCl ratio of 2.0, a reaction time of 3 h, a reaction temperature of 15.0 ℃, a volume fraction of ionic liquid to the mixture (isopropyl bromide, n-dodecane and n-hexane) of 9%, and a naphthalene/isopropyl bromide molar ratio of 4.0. Under the optimal reaction condi -tions, the conversion of isopropyl bromide reached 98% and the selectivity of 2-isopropyl naphthalene was equal to 80%. The test results verified good catalytic activity upon using Et 3NHCl-AlCl 3 ionic liquid as the catalyst for alkylation of naph-thalene with isopropyl bromide. The activity of the ionic liquid remains unchanged after it has been recycled for 4 times.Key words: ionic liquid; naphthalene; isopropyl bromide; alkylation

the petroleum industry. In addition to their ‘green’ nature, ionic liquids are often referred to as ‘designable solvents’, because their physical properties, including melting point, viscosity, density, solubility, and acidity/coordination properties, can be tuned according to different reactions or processes by altering the combination of their cations and anions [12-17]. Alkylation of naphthalene with isopropyl bromide to form 2-isopropyl naphthalene was carried out by using the ionic liquid triethylamine hydrochloride-aluminum chloride as the catalyst under optimal reaction conditions. The effect of the proportion of catalyst itself, the reaction time, the reaction temperature, the ionic liq-uid dosage as well as the molar ratio of reaction materials was studied. Besides, the recyclability of ionic liquid was also investigated.2　Experimental

2.1　Preparation of ionic liquid

The ionic liquid used in these experiments was prepared according to the procedure referred to in literature [18-19]. In