145729-05-1Relevant articles and documents
Synthesis, thermochemistry, and reactions of vicinal bis(azoalkanes). The chemistry of α- and β-azo radicals
Engel, Paul S.,Wang, Chengrong,Chen, Yanqin,Rüchardt, Christoph,Beckhans, Hans-Dieter
, p. 65 - 74 (2007/10/02)
Two vicinal bis(azo)alkanes, 8P and 8B, were prepared from acetone phenylhydrazone (APH) and acetone tert-butylhydrazone (ATBH), respectively. Thermolysis of 8P above 130°C in the presence of thiophenol affords APH in quantitative yield, showing that the central C-C bond of 8P cleaves in preference to the usual C-N homolysis of azoalkanes. The resulting radicals 9P recombine to the C-N dimer 16P about 40 times faster than to the more stable C-C dimer 8P. From the combustion heat of 8P, we deduce that its strain enthalpy Hs is 5.5 kcal/mol, while the resonance stabilization energy (RSE) of 9P is 15.3 kcal/mol. The tert-butyl analog 8B loses 2 mol of N2, showing that C-N homolysis greatly dominates over C-C homolysis. Nevertheless, we estimate that the latter process would occur with ΔG* (150°C) > 40.3 kcal/mol, which implies that the RSE of aliphatic hydrazonyl radical 9B is at least 6 kcal/mol below that of 9P and is little or no more than the RSE of the 1,1-dimethylallyl radical.
