Vanishing Microwave Effects: Influence of Heterogeneity

A consistent setup of experiments has been conducted to demonstrate an enhanced reaction rate under microwave irradiation as compared to conventional heating, i.e. a real microwave effect. It was found that addition of a cosolvent, diminishing the heterogeneous character of the reaction mixture, greatly reduced the microwave effect. This was demonstrated by two examples; selective mono-urea formation and racemization of an N-acetylamino acid. Furthermore, formation of a Grignard reagent was accelerated under MW irradiation by electrostatic etching of the metal surface. The microwave effect observed in these reactions seems to rely on heterogeneity and specific interactions on the solid–liquid interface. Basic understanding of these findings is crucial for scaling up microwave assisted processes

Lipase-Catalyzed Ring-Opening Copolymerization of ε‑Caprolactone and β‑Lactam

The enzymatic ring-opening copolymerization of ε-caprolactone (ε-CL) and β-lactam by using Candida antarctica lipase B (CAL-B) as catalyst was studied. Variation of the feed ratios of 25:75, 50:50, and 75:25 of ε-CL/β-lactam was performed. The products contain poly(ε-CL-co-β-lactam) and the homopolymers of poly(ε-CL) and poly(β-lactam). The structure of the copolymers was determined by MALDI-ToF MS. Poly(ε-CL-co-β-lactam) has an alternating and random structure consisting of alternating repeating units with oligo(ε-CL) or oligo(β-lactam). The highest fraction of the alternating copolymers resulted from the reaction with a feed ratio 50:50. The copolymer is a semicrystalline polymer with a Tm at 124 °C and Tgs at −15 and 50 °C. Interestingly, the copolymer also demonstrated cold crystallization at 29 and 74 °C, after quenching the sample from the melt in liquid nitrogen.