Synthesis of N-vinyl caprolactam

The synthesis of N-vinyl caprolactam (NVCL), with acetylene as alkylene agent, was studied in a stirred reactor system. With potassium hydroxide (KOH) being used as catalyst and 18-crown-6 ether as cocatalyst, NVCL was synthesized by the reaction of acetylene with caprolactam (CL). Crude products were purified by vacuum distillation. The addition of 18-crown-6 ether accelerates the reaction rate of the nucleophilic addition much greatly. The initial explanation suggests that the hole radius of 18-crown-6 ether is close to the one of K+. A complex is formed between 18-crown-6 ether and K+ ion on the formed intermediate of potassium caprolactam, so the addition reaction between acetylene and caprolactam was accelerated greatly. In the stirred tank reactor (500 mL four flask bottle), the CL conversion is 30.5% and the product selectivity is up to 73.4%. The experimental data indicate that the product mixture is a non-ideal liquid mixture. A single process of distillation is difficult to obtain a high purity NVCL product. The combination of extraction and distillation is an ideal separation process for producing high purity NVCL.