The Role of the Interface in Thin Film and Droplet Accelerated Reactions Studied by Competitive Substituent Effects

Based on a study of competitive substituent effects in a Claisen-Schmidt reaction, interfacial effects have been shown to play an important role in accelerated reactions that occur in thin films and droplets. A role for the interface in an accelerated C-C bond-formation reaction between 6hydroxy-1-indanone and aromatic aldehydes is indicated by cooperative interactions between p-methylbenzaldehyde and p-nitrobenzaldehyde. Additional acceleration over that occurring in bulk reactions is seen for p-methylbenzaldehyde, but only in the presence of p-nitrobenzaldehyde. A decrease in the degree of acceleration is detected when the reaction is forced electrostatically to occur inside the thin film, and the interface is shown to participate in the accelerated reactions. This experimental evidence for interfacial thin film and droplet acceleration supports a recent model and builds on earlier work which locates molecules within evaporating droplets in electrosprays.