A model for a solvent-free synthetic organic research laboratory: click-mechanosynthesis and structural characterization of thioureas without bulk solvents
作者:Vjekoslav Štrukil、Marina D. Igrc、László Fábián、Mirjana Eckert-Maksić、Scott L. Childs、David G. Reid、Melinda J. Duer、Ivan Halasz、Cristina Mottillo、Tomislav Friščić
DOI:10.1039/c2gc35799b
日期:——
The mechanochemical click coupling of isothiocyanates and amines has been used as a model reaction to demonstrate that the concept of a solvent-free research laboratory, which eliminates the use of bulk solvents for either chemical synthesis or structural characterization, is applicable to the synthesis of small organic molecules. Whereas the click coupling is achieved in high yields by simple manual grinding of reactants, the use of an electrical, digitally controllable laboratory mill provides a rapid, quantitative and general route to symmetrical and non-symmetrical aromatic or aromatic–aliphatic thioureas. The enhanced efficiency of electrical ball milling techniques, neat grinding or liquid-assisted grinding, over manual mortar-and-pestle synthesis is demonstrated in the synthesis of 49 different thiourea derivatives. Comparison of powder X-ray diffraction data of mechanochemical products with structural information found in the Cambridge Structural Database (CSD), or obtained herein through single crystal X-ray diffraction, indicates that the mechanochemically obtained thiourea derivatives are pure in a chemical sense, but can also demonstrate purity in a supramolecular sense, i.e. in all structurally explored cases the product consisted of a single polymorph. As an extension of our previous work on solvent-free synthesis of coordination polymers, it is now demonstrated that such polymorphic and chemical purity of selected thiourea derivatives, the latter being evidenced through quantitative reaction yields, can enable the direct solvent-free structural characterization of mechanochemical products through powder X-ray diffraction aided by solid-state NMR spectroscopy.
异硫氰酸酯与胺的机械化学点击偶联反应已被用作模型反应,证明了无溶剂研究实验室的概念适用于小有机分子的合成,该概念消除了化学合成或结构表征中对大量溶剂的使用。虽然通过简单手动研磨反应物可以实现高产率的点击偶联,但使用电动、数字可控的实验室研磨机提供了一种快速、定量且普遍适用的方法,用于合成对称和非对称的芳香或芳香-脂肪族硫脲。与手工研钵合成相比,电动球磨技术(干磨或液体辅助研磨)在合成49种不同的硫脲衍生物中展示了其效率的提升。通过将机械化学产品的粉末X射线衍射数据与剑桥结构数据库(CSD)中的结构信息或通过单晶X射线衍射获得的信息进行比较,表明机械化学合成的硫脲衍生物在化学意义上是纯净的,同时在超分子意义上也可以是纯净的,即在所有结构探索的情况下,产品只包含一种多晶型物。作为我们之前关于无溶剂合成配位聚合物工作的延伸,现在证明了选定的硫脲衍生物的多晶型和化学纯度(后者通过定量反应产率得到证实)能够通过粉末X射线衍射辅助的固态核磁共振光谱直接进行无溶剂的结构表征。