Kinetics of Epoxidation of Hydroxyl-Terminated Polybutadiene with Hydrogen Peroxide under Phase Transfer Catalysis
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- 作者：Qingfa Wang ; Xiangwen Zhang ; Li Wang ; Zhentao Mi
- 刊名：Industrial & Engineering Chemistry Research
- 出版年：2009
- 出版时间：February 4, 2009
- 年：2009
- 卷：48
- 期：3
- 页码：1364-1371
- 全文大小：224K
- 年卷期：v.48,no.3(February 4, 2009)
- ISSN：1520-5045
文摘
The epoxidation of hydroxyl-terminated polybutadiene (HTPB) via phase transfer catalysis (PTC) using H2O2 as the oxidant and ammonium tungstate hydrate and phosphoric acid as the cocatalysts was successfully carried out in an acidic solution/organic solvent two-phase medium. The microstructures of original and epoxidized HTPB products were confirmed by 1H NMR and 13C NMR. The influence of some process variables such as stirring speed, ammonium tungstate hydrate amount, Aliquat 336 amount, phosphoric acid amount, hydrogen peroxide amount, and reaction temperature on the epoxidation of HTPB were studied in detail. The reactions in organic phase were the rate-controlling steps. Based on the experimental results, a rational PTC mechanism was proposed and a pseudo-steady-state kinetic model was applied to describe the epoxidation of HTPB. The apparent kinetic constants for the three configurations in HTPB under the temperatures of 20−60 °C were determined (kapp,c = (2.7−6.43) × 10−2 min−1, kapp,t = (0.95−4.49) × 10−2 min−1, kapp,v = (0.08−0.65) × 10−2 min−1). The activation energies of cis, trans, and vinyl configurations in the epoxidation of HTPB were 19.72, 31.35, and 90.75 kJ mol−1, respectively. This method (Aliquat 336 as PTC/H2O2/ammonium tungstate hydrate and phosphoric acid as the cocatalysts) was very effective for the epoxidation of HTPB. The chemoselectivity of epoxidation of three configurations in HTPB (cis, trans, and vinyl) was evaluated. The reactivity of double bonds toward epoxidation, depending on the chain microstructure, decreased in the following order: 1,4-cis > 1,4-trans > 1,2-vinyl.