62545-70-4Relevant academic research and scientific papers
Pressure Effects on Azocumene Decomposition Rates, Efficiencies of Radical Production, and Semibenzene Dimers
Neuman, Robert C.,Amrich, Michael J.
, p. 4629 - 4636 (2007/10/02)
Rates of thermal decomposition of azocumene (1a) and p,p'-dimethylazocumene (1b) in cumene or chlorobenzene are decreased by pressure with decomposition activation volumes of +5 cm3/mol (1a,cumene), +4.3 cm3/mol (1a,chlorobenzene) and +4.6 cm3/mol (1b,cumene).Efficiencies (f) of radical production, with di-tert-butyl nitroxide (DBNO) or thiophenol as scavengers, decrease with pressure; however, the pressure dependence of f with DBNO is anomalous.This is explained by the formation of semibenzene dimers as cage products, which subsequently decompose to give cumyl radicals.The corresponding α-ortho semibenzene dimers of cumyl radicals are formed from both 1a and 1b.The α-para semibenzene dimer from decomposition of 1a in chlorobenzene appears to rearrange to give p-cumylcumene.No such rearrangements appears to occur from the α-ortho dimers nor is it likely that any α-para dimer is formed from 1b decomposition.An apparent activation volume for thermal decomposition of the α-ortho semibenzene dimer in cyclohexane at 20 deg C is ca. +6 cm3/mol.Pressure favors disproportionation over coupling for geminate cumyl radicals.
Decomposition of Azocumene on Silica Surfaces
Leffler, J. E.,Zupancic, J. J.
, p. 259 - 267 (2007/10/02)
The decomposition of azocumene on silica surfaces in the absence of solvent is slower than in toluene solution and has a much lower radical efficiency.Radicals that escape geminate reaction can be trapped by adsorbed bisdiphenylenephenylallyl.The ratio of cumene to α,α-dicumyl is about five times that in toluene.Aromatized α-ortho and α-para cumyl dimers, found only in the reactions on silica, are formed in low yield.These products (10 and 11) are formed via the quinoidal α-ortho and α-para dimers, which have been reported as transient products in toluene.The aromatized dimers (10 and 11) are exclusively geminate recombination products, presumably because they are formed only if the site at which the azocumene decomposes is also a catalytic site for the aromatization of the quinoidal dimers.The rates and product ratios depend to some extent on the purity and degree of hydroxylation of the silica.They also depend on the fraction of a monolayer occupied by the azocumene.At low monolayer coverages the azocumene is preferentially adsorbed on sites that give lower rates, higher cumene to α,α-dicumyl ratios, and higher yields of the aromatized dimers 10 and 11.The silicas were characterized by their acidities, Rf values, catalytic properties, and the electron paramagnetic resonance spectra of adsorbed radicals.
