Accelerated C-N Bond Formation in Dropcast Thin Films on Ambient Surfaces

The aza-Michael addition and the Mannich condensation occur in thin films deposited on ambient surfaces. The reagents for both C-N bond formation reactions were transferred onto the surface by drop-casting using a micropipette. The surface reactions were found to be much more efficient than the corresponding bulk solution-phase reactions performed on the same scale in the same acetonitrile solvent. The increase in rate of product formation in the thin film is attributed to solvent evaporation in the open air which results in reagent concentration and produces rate acceleration similar to that seen in evaporating droplets in desorption electrospray ionization. This thin film procedure has potential for the rapid synthesis of reaction products on a small scale, as well as allowing rapid derivatization of analytes to produce forms that are easily ionized by electrospray ionization. Analysis of the derivatized sample directly from the reaction surface through the use of desorption electrospray ionization is also demonstrated.