Wei Zengfeng, Chen Xin, Duan Jiang, Mei Caihong, Xiao Dan, Zhang Aidong
Key Laboratory of Pesticide & Chemical Biology of the Ministry of Education, College of Chemistry, Central China Normal University Wuhan 430079 P. R. China
RSC Adv. 2019 Aug 12;9(43):24904-24914. doi: 10.1039/c9ra04981a. eCollection 2019 Aug 8.
Urushiol is a resource-limited natural coating material with diverse applications; however, the synthesis of urushiol analogues and the realization of their urushiol-like performance remain challenging. Herein, four urushiol analogues, namely, 3-((4-alkenoylpiperazin-1-yl)methyl)catechols with the precise 3-substitution pattern on a catechol as that found in urushiol were synthesized by employing the Mannich reaction of catechol with formaldehyde and -Boc-piperazine as the key step in a two-step route. By using optimization, the advantages of convenience in operation, cost-effectiveness, and scalability could be obtained. The electropolymerization of these analogues on copper was found to be practical due to their higher aerobic stability than urushiol, affording robust coatings with desirable hardness, adhesion strength, hydrophobicity, and thermal stability. Furthermore, the coatings exhibited effective corrosion protection on copper with initial anticorrosion efficiency up to 99.9% and comparatively higher efficiency (more than 97%) after 4 weeks of immersion in 3.5 wt% NaCl solution. The evidence from the electrochemical and infrared spectroscopic characterization data revealed that the electropolymerization process mechanically involved the free radical coupling of phenoxyl radicals to themselves and to the C[double bond, length as m-dash]C bonds in the side chain, forming a robust crosslinking coating. This work paves a way for the synthesis of high-performance urushiol analogues with potential applications as metal protection materials.
漆酚是一种资源有限但具有多种应用的天然涂层材料；然而，漆酚类似物的合成及其类漆酚性能的实现仍然具有挑战性。在此，通过采用邻苯二酚与甲醛以及 -Boc-哌嗪的曼尼希反应作为两步路线中的关键步骤，合成了四种漆酚类似物，即具有与漆酚中邻苯二酚上精确的3-取代模式相同的3-((4-烯丙酰基哌嗪-1-基)甲基)邻苯二酚。通过优化，可以获得操作方便、成本效益高和可扩展性强的优点。由于这些类似物比漆酚具有更高的需氧稳定性，发现在铜上对它们进行电聚合是可行的，可提供具有所需硬度、附着力、疏水性和热稳定性的坚固涂层。此外，这些涂层对铜表现出有效的腐蚀防护作用，初始防腐效率高达99.9%，在3.5 wt% NaCl溶液中浸泡4周后效率相对较高（超过97%）。电化学和红外光谱表征数据的证据表明，电聚合过程在机械上涉及苯氧基自由基自身之间以及与侧链中C[双键，长度为m破折号]C键的自由基偶联，形成坚固的交联涂层。这项工作为合成具有作为金属保护材料潜在应用的高性能漆酚类似物铺平了道路。
