We used infrared (IR)-thermography for the rapid screening of a series of rare earth triflates for their catalytic activity in (i) the ring opening of epoxides by alcohols, and (ii) the Baeyer-Villiger oxidation of cyclobutanones with hydrogen peroxide. Both reactions are characterized by significant negative reaction enthalpies, thus they are ideally suited for thermographic detection. We discovered that scandium(III) is an outstandingly active catalyst for the ring opening of epoxides. In the case of the Baeyer-Villiger oxidation, again scandium(III) performed best, followed closely by neodymium(III). For both reaction types, scandium was not reported before as a catalyst. (C) 2003 Elsevier Science B.V. All rights reserved.