Addition of secondary amines to α,β-unsaturated carbonyl compounds and nitriles by using microstructured reactors

Several additions of amines to alpha,beta-unsaturated carbonyl compounds (Michael additions) were performed in a continuous-flow microstructured reactor rig and compared to the respective batch reaction. Dimethylamine/diethylamine/piperidine and acrylic acid ethyl ester/acrylonitrile were employed as two sets of reactants, giving six reactions. Some of these reactions are highly exothermal. Using the traditional batch procedure the olefin must be added quite slowly to the diluted amine to ensure temperature control and safe operation; especially this is necessary for the addition of dimethylamine (40 mass % aqueous solution) to acrylonitrile. Good yields (>85%) are achieved in this way; however, processing time is very long (17-25 h). To reveal the intrinsic kinetic potential and thus to accelerate these reactions, the reactants were mixed in a continuous-flow microstructured reactor rig which allows rapid mixing and efficient removal of the reaction heat. In this way, reaction time was decreased to a few seconds up to about half an hour, which is a change by 2 orders of magnitude. While the yields achieved with the continuous-flow microstructured reactor rig matched those for the batch procedure, the space-time yields for the microflow processing are much higher, in the best case by a factor of about 650.