作者:Min Jeong Hyun、Mi Shin、Yong Jin Kim、Young-Woong Suh
DOI:10.1007/s11164-015-2224-x
日期:2016.1
In catalytic decomposition of dimethylhexane-1,6-dicarbamate (HDC) into hexamethylene-1,6-diisocyanate (HDI), Zn-containing homogeneous (i.e., zinc acetate) and heterogeneous (i.e., ZnO) catalysts were active among a number of catalysts tested, due to the great electron withdrawing ability of Zn ions. Particularly, when polyethylene glycol dimethyl ether was used as a solvent, ZnO was found to be relatively robust, because the catalytic performance was maintained up to the third use (HDC conversion of 93 % and HDI yield of 67 % at 180 °C for 1 h). Through investigation of a HDC/ZnO mixture at elevated temperatures by IR spectroscopy, a possible reaction scheme of ZnO-catalyzed decomposition of HDC was proposed. The H atom is removed from the N–H group of HDC by hydrogen bonding with an O site on the ZnO surface, followed by coordination of an O–C=O group in monodentate mode to a Zn site. The C–O group in the O–C=O linkage is then cleaved yielding the isocyanate and surface methoxide species. Finally, methanol is released from ZnO by a reaction between the surface methoxide and the hydroxyl species.
在催化二甲基-1,6-己烷二甲酸酯(HDC)分解为六亚甲基-1,6-二异氰酸酯(HDI)的过程中,由于锌离子具有很强的电子撤回能力,因此在测试的多种催化剂中,含锌均相催化剂(即醋酸锌)和异相催化剂(即氧化锌)具有很强的活性。特别是在使用聚乙二醇二甲醚作为溶剂时,ZnO 的催化性能一直保持到第三次使用(在 180 ℃ 1 h 条件下,HDC 转化率为 93 %,HDI 产率为 67 %),因此 ZnO 的催化性能相对较强。通过红外光谱对高温下 HDC/ZnO 混合物的研究,提出了 ZnO 催化 HDC 分解的可能反应方案。H 原子通过与 ZnO 表面的一个 O 位点发生氢键作用而从 HDC 的 N-H 基团上脱落,然后一个 O-C=O 基团以单配位模式配位到一个 Zn 位点上。然后,O-C=O 连接中的 C-O 基团被裂解,产生异氰酸酯和表面甲氧基。最后,通过表面甲氧基和羟基的反应,甲醇从氧化锌中释放出来。