Urea Decomposition:Efficient Synthesis Of Pyrroles Using The Deep Eutectic Solvent Choline Chloride/Urea

In recent years,low cost and environmentally friendly solvent system-deep eutectic solvent(DES)has attracted the attention of scientists and researchers.Deep eutectic solvent(DES)is a new type of green solvent.Compared with traditional solvents,it has low volatility,biodegradability,reproducibility,low toxicity,wide electrochemical stability window,and a large amount of organic or Inorganic compounds have high solvency and other advantages.Has been widely used in the separation process and chemical transformation.Although DES has a wide range of applications,its stability has rarely been studied.Choline chloride/urea is a relatively common eutectic solvent in DES.Little is known about the stability of urea in this system.Urea is a relatively stable chemical substance.However,it can also be decomposed into ammonia and carbon dioxide when using suitable catalysts and thermal conditions.The urea-containing DES system has a thermal decomposition temperature of more than 200°C.However,in our experiments it was found that DES can be partially decomposed at 80°C in the presence of certain media.This article mainly describes the lack of stability of the deep eutectic solvent choline chloride/urea system.And the use of this feature of the system in the synthesis of pyrrole and its derivatives in the application.The pyrrole heterocyclic ring is one of the important functional groups or parent nucleus with biological activity in the five-membered heterocyclic ring,and has an antifungal effect and anti-tumor,anti-hypertensive and other pharmacological activities.One of the most common methods for the synthesis of pyrrole compounds is the Knorr synthesis method,which is formed by the condensation of an ?-amino ketone with an ?-haloketone followed by condensation with a ?-ketone ester.We performed the Paal-Knorr furan synthesis using a tricarbonyl compound in a deep eutectic solution of choline chloride/urea and found that without the addition of ammonia,the reaction produced the corresponding pyrrole product.This further explains the lack of stability of the deep eutectic solvent system of choline chloride/urea.In this paper,it is reported that as a component of the deep eutectic solvent of choline chloride/urea,urea is easily decomposed in particular in the presence of a ketone carbonyl group in the tricarbonyl compound,and a simple and effective pyrrole synthesis method is described by the use of chlorine.The deep eutectic solvent of choline/urea is produced in situ by the condensation of ammonia with a series of tricarbonyl compounds.