고순도 1,4-Sorbitan을 이용한 저융점 Sorbitan Monostearate의 합성

Abstract

Surfactants are classified depending on the charge of the surface - active moiety, usually the large part of the molecules, into anionic, cationic and nonionic surfactant. Sorbitan monostearate(Span 60), nonionic surfactant, has been used as an anti - fogging agent for plastic films. Conventional synthetic method of sorbitan monostearate was esterfication of D-sorbitol with stearic acids at elevated temperature. However, the purity and the color of the sorbitan monostearate are not proper for the anti - fogging agent. This research established the efficient process to synthesize highly pure sorbitan monostearate with low melting point. The process composed of two separated stages. At first stage, starting material, D-sorbitol, was decomposed into pure 1,4-sorbitan under acidic catalyst. The 1,4-sorbitan was finally reacted with stearic acid to give highly pure sorbitan monostearate with low melting point. In the fisrt stage, for the synthesis of highly pure 1,4-sorbitan solution from D-sorbitol, some experimental studies were performed. The reaction showed first order reaction with activation energy of 118.3 KJ/mol. Color of the product solutions changed to brown with reaction temperature and reaction time. The equilibrium contents of 1,4-sorbitan increased with decrease in reaction pressure, but the content of major impurity, sorbide, showed maximum about 550 torr vacuum with H3PO4 catalyst. The reasonable catalyst configuration was 0.26 wt% PTSA and 1 wt% H3PO2 and optimum reaction temperature and pressure range was 110 ～ 120℃ and 700 ～ 720 torr vacuum, respectively. At optimum reaction conditions, we could obtain white product solutions of highly pure 1,4-sorbitan with sorbide less than 10 wt%. This white product solution is advantageous for preparation of high quality span, anti-fogging agent. In the second stage, nonionic surfactant, sorbitan monostearate, has been prepared by esterification of stearic acid with some starting materials(1,4-sorbitan and/or sorbitol). The effects of starting materials and catalysts on the purity and melting point of nonionic sorbitan monostearate have been experimentally investigated. We could obtain low melting point sorbitan monostearate from highly pure 1,4-sorbitan with NaOH as catalyst. The synthesized sorbitan monostearate was identified with NMR and FT-IR, and the compositions were analyzed with GC. The acid value and melting point of sorbitan monostearate synthesized with optimum conditions were 7.15 and 48.5℃ respectively. These values suggests that sorbitan monostearate synthesized in this research may be more efficient for the anti-fogging agent than our reference material whose melting point is 53℃.