Thermolysis of polyazoalkanes and the radical stabilizing effect of azo and azoxy groups
Engel, Paul S.
Doctor of Philosophy
An unique linear aliphatic trisazoalkane was synthesized. Its thermolysis proceeded stepwise to yield seven fragments, with an overall reaction enthalpy of -93.6 kcal/mol, 66.6 kcal/mol lower than that for azo-t-butane. Due to the stepwise feature, the difference in overall reaction enthalpy resulted in only an 8.6 fold rate increase for the trisazoalkane relative to azo-t-butane at 153.46°C. Photolysis of a novel cyclic azimine obtained during the synthesis of the trisazoalkane yielded a highly strained triaziridine and an unusual triazane. The triaziridine rapidly reverted to the azimine with a rate constant of 2.05 x 10-4 s-1 at 24.4°C. Arylmethylenecyclopropanes with para azo, azoxy and other related N-containing substituents were synthesized to study radical stabilizing effects. The order of increasing radical stabilizing ability was determined to be -N(O)=NBu-t, -N3, CH=NBu-t, -N=NBu-t, -NH2, -CH=NOMe, -CH=NNMe 2, -N=N(O)Bu-t, -N=NPh and -CH=N(O)Bu-t. The last three groups, azoxy, nitrone and phenylazo, were the best non-ionic radical stabilizers ever studied. The large rate enhancements in the thermal rearrangement resulted from radical stabilization through spin delocalization by the para-substituents in the transition state. A cumyl type 1,3,5-trisazoalkane and its monoazo, para-bisazo and meta-bisazo analogs were synthesized. Thermolysis of C3 and C4 followed a stepwise mechanism; that is, the two azo groups decomposed sequentially. Mathematical models were developed for analyzing the kinetics data. The rate constants for these azoalkanes increased statistically with the number of -N=N-groups. In addition to the stepwise mechanism, the para-bisazo compound also decomposed concertedly to a quinodimethane. To demonstrate that the 1,3,5-triazoalkane could serve as a radical initiator, different trapping products were made by thermolysis of the 1,3,5-trisazoalkane in the presence of PhSH and nitroxyl radicals. In the binary system of C4 and TEMPO, low polydispersity (1.13) was obtained for polystyrene.
Organic chemistry; Polymer chemistry