A series of solvent-free condensation reactions have been studied calorimetrically, with the goal of determining feasibility of scale-up in the realisation of potentially greener processes, in which the use of auxiliary compounds, such as solvents, are obviated. Knoevenagel reactions leading to intermediates used in the production of 1,4-dihydropyridine drugs, and in drug libraries currently under testing, exhibit a reaction exotherm ascribed almost entirely to the formation of the imminium ‘Knoevenagel’ intermediate, which may be controlled by regulation of the quantity of catalyst. Reactions to form stable imines and cyanoamide products are also demonstrated to be exothermic.