Free-Radical Reactions of Pyrroles

Abstract

Free-Radical Reactions of Pyrroles 1163 the reaction subsided and the system had reached room temperature. The reaction mixture was worked up by distillation and trituration with ligroin to give a crystalline solid. The recrystallized product, m.p. 69°, 3.1 g., was obtained in 28% yield. The infrared spectrum of the solid coincided with that of the prepared phenyl sulfoxide. Mixture melting technique gave no depression.

Exploring Functionalities for the Development of High Thermal Stability Polypropylene-Based Dielectrics

“…The aforementioned possibility of chain cross-linking during heating arises from the labile character of the α-methylene C–H bonds of N -alkylpyrrole units, which are expected to undergone homolytic scission under the action of heat, oxygen or pre-existing PP hydroperoxides. Thereby, relatively stable benzyl-like radicals are generated and eventually combined with each other, as it has been described in the literature and is shown in Scheme . This process occurs at high temperatures, likely together with the also described radical addition of the above-mentioned radical on another pyrrole ring, and lay behind the pursued stabilization effect of the N -alkylpyrrole function.…”

“…without any intermediate copolymer post-modification. Among functionalities with such potential, we thought about the N-alkyl-pyrrole moiety because of its enhanced propensity to yield benzyl-like radicals through α-hydrogen abstraction, in the presence of peroxides, and to eventually yield intermolecular addition 28 . Such peculiarity would make it suitable, not only to trap radical activity in initial degradation stages of a thermoplastic polyolefin, but also to prevent mechanical damage by promoting selective chain crosslinking.…”

“…A detailed analysis of the 1 H-NMR spectrum confirmed, indeed, the presence of proton traces at 3.44 ppm and 3.66 ppm, which were ascribed to methine protons arising from coupling between N-alkylpyrrole branches. Such signals are shown in Figure 2 and their assignment was made on the basis of the 1 H-NMR spectrum predicted for the expected chemical structure, according to the distinctive radical reactivity of Nalkylpyrroles 28 (see spectrum in Figure S5). The spectrum in Figure 2 displays one triplet and one double triplet, slightly above and below the predicted value (3.5 ppm) respectively, which correspond to the diasterotopic methine protons of the resulting two chiral carbons.…”

“…Among functionalities with such potential, we thought about the N-alkylpyrrole moiety because of its enhanced propensity to yield benzyl-like radicals through αhydrogen abstraction, in the presence of peroxides, and to eventually yield intermolecular addition. 15 Such peculiarity would make it suitable, not only to trap radical activity in initial degradation stages of a thermoplastic polyolefin but also to prevent mechanical damage by promoting selective chain cross-linking. Furthermore, such thermally promoted radical chemistry would allow reactive processing of PP, in order to get net cross-linking without scission and oxidation, as well as tailored reticulation degrees.…”

“…A detailed analysis of the 1 H NMR spectrum confirmed, indeed, the presence of proton traces at 3.44 and 3.66 ppm, which were ascribed to methine protons arising from coupling between N-alkylpyrrole branches. Such signals are shown in Figure 2, and their assignment was made on the basis of the 1 H NMR spectrum predicted for the expected chemical structure, according to the distinctive radical reactivity of N-alkylpyrroles 15 (see spectrum in Figure S5).…”