Comparative Experimental Study on the Energy Efficiency of Nontraditional Activations in Catalyst-Free Processes

The energy efficiencies of high hydrostatic pressure, microwave, and ultrasonic activation methods were compared to that of traditional heating in three types of reactions, the carbonyl−hydrazine condensation, the Paal−Knorr pyrrole synthesis, and the O-acetylation of salicylic acid. Each of the carbonyl−hydrazine condensation and the Paal−Knorr pyrrole synthesis was investigated via two examples using substituted derivatives as starting materials. The energy consumption of the reactions by each method was determined, and the normalized energy consumption, defined as power usage per percent yield, was calculated. Based on the data obtained, high hydrostatic pressure and probe sonication appeared as the most energy efficient activation methods for four of the five model reactions.