According to the reports on the research work of direct dehydration method, the catalytic dehydration reaction of a-NHP requires relatively harsh conditions, the yield of the product is often low, and it is difficult to obtain a dehydration catalyst that meets the requirements of industrial production, so the indirect dehydration method is produced.
The reaction process of the indirect dehydration method is mainly divided into three steps: one step is the same as that of the direct dehydration method, which is the aminolysis reaction of r butyrolactone and ethanolamine to obtain α-NHP; The second step is the halogenation reaction of a-NHP, that is, the hydroxyl group in the α-NHP molecule is converted into halogens with a halogenated agent, and then the α-NHP is converted into haloethylpyrrolidone, such as chloroethyl pyrrolidone; Compared with the direct dehydration method, the reaction conditions are milder than the direct dehydration method, but at the same time, it also has its shortcomings, that is, there are relatively many reaction steps, the process flow is longer, the raw materials used are more, the by-products are more, and the post-treatment process is cumbersome, which will cause environmental pollution.
As far as industrialization is concerned, the -butyrolactone method generally has the problems of high raw material price and high production cost. However, compared with the acetylene method, the Y-butyrolactone method has a short process flow and small equipment. With the advantages of short construction period and mild operating conditions, it is more suitable for small and medium-sized manufacturers of NVP. It can be seen that both the acetylene method and the y-butyrolactone method have their own shortcomings, so there are still a large number of scientific and technological workers engaged in the research and production of NVP and its polymer PVP.
The research on the synthesis of NVP and PVP by y-butyrolactone as raw material began in the 40s of the 20th century, because it is based on y-butyrolactone as the main starting material, it is called y-butyrolactone method α α. The second step is to carry out the intramolecular dehydration reaction of α-NHP in the presence of a dehydration catalyst, and remove a molecule of water to obtain the monomer NVP α. In addition to the main acetylene method and y-butyrolactone method, there are other synthesis methods, such as pyrrolidone method for direct generation of NVP by reacting pyrrolidone and ethylene under the action of palladium catalyst, all of which will be introduced and discussed in the relevant chapters below.
