Thermolysis of Free-Radical Initiators:  tert-Butylazocumene and Its 1,3- and 1,4-Bisazo and 1,3,5-Trisazo Analogues

Abstract

Four tert-butylazocumenes (4-7) were prepared from the corresponding cyanobenzenes, and their nitrogen evolution kinetics and products were analyzed. In combination with TEMPO, the simplest compound, tert-butylazocumene (4), shows promise as a "one-radical" initiator of styrene polymerization. The ABNO-trapped cumyl radical 29 is a particularly stable trialkylhydroxylamine, whose thermolysis half-life is 2.1 h at 150 degrees C. Taking advantage of this stability, we trapped the cumyl radical centers from 7 to afford tris adduct 32a. While the behavior of the meta bisazoalkane 6 can be mostly predicted from that of 4, the para isomer 5 exhibits both unusual products and kinetics, attributed to the formation of quinodimethane 33 via azo-containing radical 34. In fact, flash vacuum pyrolysis of 5 allowed observation of the (1)H and (13)C NMR spectra of 33, whose persistence even at ambient temperature showed that this quinodimethane is far more stable than the parent 36. Finally, evidence is presented that 7 is an initiator of star polymerization.

Synthesis of 2,5-Diaryl-1,5-dienes from Allylic Bromides Using Visible-Light Photoredox Catalysis

“…R f 0.52 (10% ethyl acetate/hexanes); 1 H NMR (500 MHz, CDCl 3 ): δ 7.61 (d, J = 8.5, 2H), 7.54 (d, J = 8.5, 2H), 5.47 (s, 1H), 5.25–5.24 (m, 1H), 2.16 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ): δ 145.8, 141.9, 132.2, 126.2, 119.1, 115.8, 111.0, 21.6. Characterization data obtained matched those previously reported in the literature. , …”

Photolysis of an asymmetrically substituted diazene in solution and in the crystalline state

“…The synthesis of asymmetrically substituted diazenes is found in the literature. 14 The synthesis is done beginning with an alcohol and an amine.…”

6 Reaction mechanisms : Part (iii) Radical and radical ion reactions

“…Engel et al studied various aspects of tert-butylazocumene (73) and its multiply substituted analogs (74, 75, and 76). 37 The kinetics of nitrogen evolution have been measured and the first deazetation rate increases with the number of tert-butyl azo groups on the ring. The behavior of 74 varies slightly from the rest, as deazetation produces a diquinonemethide.…”