APPLIED CHEMISTRY Study on the Synthesis of Benzoic Acid Esters by Transesterification of Crude Methyl Benzoate†
Shaokun Tang and Shufen Li*
School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, China
According to the need of reclamation and utilization of the byproducts crude methyl benzoate in the production ofterephthalic acid dimethyl ester by the Witten-Hercules method, the processes of the preparation of benzoic acid esters such as benzyl and butyl benzoate by transesterification of crude methyl benzoate were studied. The processes of the synthesis of benzyl and butyl benzoate were investigated using different technologies including batch rank reaction and reactive distillation. The results showthat benzoic acid esters can be obtained particularly easily with high conversions without the formation of additional byproducts, the catalyst titanate has a high activity, and the reaction conversions of the preparation of benzyl and butyl benzoate are respectively up to 100% and 82.79% under the proper conditions.
Introduction Terephthalic acid dimethyl ester (hereinafter designated as DMT) isproduced worldwide in great quantities by the Witten-Hercules method. During this production, considerable amounts of methyl benzoate containing waste product (below designated as crude B-ester) are thereby produced, which are always conveyed to waste combustion or cheaply sold. However, B-ester (namely, methyl benzoate) with a high degree of purity can be used extensively as perfumes and solvents,and the crude B-ester can also serve as a raw material for the production of sodium benzoate, plasticizer, and benzoic acid ester of monoalcohols higher than methanol such as butyl benzoate, benzyl benzoate, and so on.1-3 Butyl benzoate is widely used as the menstruum of cellulose esters, the material of plasticizers and flavors, and the dyestuff carrier of variegating polyester fibers. Benzylbenzoate is mainly used in the fields of food and medicine as the solvent of fixing perfumes, seasoning candys, and synthesizing muskiness and the material of mosquito repellant oil and plasticizer. Consequently, it is important and significant for the factories that involve the reclamation of this byproduct to explore the technology of refinement and comprehensive utilization of crude B-ester. Fewattempts were made to study the technology of the preparation of benzoic acid esters from crude Bester. Only in a German Patent2 and a Japanese Patent5 were the processes described, but the reaction conditions were not optimized and reaction distillation was not used. In this paper, the processes of the synthesis of benzyl and butyl benzoate by transesterification of crude B-ester and therefinement of the products were inves† Imbursed by State Key Laboratory of Chemical Engineering of China. * To whom correspondence should be addressed. Tel.: +86-22-27408578. Fax: +86-22-27407388. E-mail: shktang@ 163.com.
tigated. Furthermore, the technologies of reactive distillation for the synthesis of benzoic acid esters were developed to further improve the reaction conversions and realize thesuccession of the technologies. Experimental Section 1. Material. Benzyl alcohol, n-butanol, and catalyst tetrabutyl titanate were purchased from reagent factories. They were analysis grade. Petrochemical Corp. of Tianjin, China, offered crude B-ester. The composition of the crude B-ester material is listed in Table 1. 2. Synthesis of Benzyl Benzoate. The reactants crude B-ester and benzyl alcoholwere added to a glass reaction kettle of 500 mL with a certain mole ratio of B-ester to benzyl alcohol and then heated. The catalyst tetrabutyl titanate was not dropped into the kettle until the reaction temperature had reached the scheduled value. The reaction preferably proceeded with the continuous removal of methanol from a short glass packed column. When methanol separation ceased, the...