Carbonylation of Acrylonitrile
The carbonylation of acrylonitrile is an important industrial process used to produce adiponitrile, which is then used to synthesize nylon 66. The reaction between acrylonitrile and carbon monoxide is catalyzed by complexes of nickel or cobalt, and it has been studied for several decades due to its technical and economic significance. The process is complex, and the main factors affecting the rate and yield of the reaction are reaction temperature, pressure, catalyst type and concentration, as well as the reactant concentrations in the reaction mixture.
The reaction between carbon monoxide and acrylonitrile proceeds via two consecutive steps. In the first step, nickel or cobalt catalyst is employed to abstract hydrogen atoms from the molecule of acrylonitrile, resulting in the formation of a nitrile ylide, which can further react to form a nitrilimine, a key intermediate of the reaction. In the second step, the nitrilimine is hydrogenated to form a linear carbon-nitrogen chain, which then undergoes global cyclization and dehydration to give adiponitrile.
The industrial production of adiponitrile generally involves a homogeneous catalytic process, in which nickel and cobalt catalysts are employed. Nickel-based catalysts are found to have higher activity than cobalt-based catalysts and the formation of byproducts is much lower. The reaction proceeds at temperatures of 100 to 200°C and at pressure of 0.3 to 1.0 MPa. The catalysts concentration range from 0.005 to 0.05 %.
In addition to the industrial use of this reaction, it has also been studied in recent years as a model system for homogeneous catalysis. Research has been focused on the investigation of reaction kinetics and mechanism as well as the development of more selective and active catalysts. For example, several recently reported catalysts have been found to be capable of selective dehydration. Also, several development have also been reported for the synthesis of hydrophobic catalysts, which can result in improved reaction selectivity and product yield.
Overall, the carbonylation of acrylonitrile is an important and well-studied process, and research is still ongoing to develop more efficient and selective catalysts and reaction conditions. The process is of great importance in the industrial production of nylon 66, which is one of the most widely used and ubiquitous polymers in the world. The understanding of the fundamentals of the catalytic reaction and improvement of the catalysts will be of great significance to the successful industrial production of nylon 66.
