Azobenzenes nitrogen-containing compounds

It is well known that nitrogen-containing ligands are readily metallated by paHadium(II). The first reaction of this type was described in 1965 by Cope et al.1 for azobenzene. Since then numerous examples of similar reactions have been described in the literature.2 These cyclometallated compounds have been shown to be reactive intermediates in organic synthesis, especially in the... 

Hint To distinguish these compounds without elemental composition or standards for GC retention time, split the GC effluent to a FID, a nitrogen-phosphorus detector, and the mass spectrometer, simultaneously. Using this splitter system, it is easy to determine if the GC peak contains nitrogen. Also, the analyst can differentiate between azobenzene and benzophenone by using the methoxime derivative. 

In the case of compounds containing the azobenzene group, oxidation has been found to occur,16 yielding either symmetrical dibenzyls or stilbenes depending on the substitution of the azobenzene. It was, however, pointed out that this is a consequence of the oxidative ability of the azo group,17 since these reactions also take place under a nitrogen atmosphere. 

A similar but mechanistically different isomerization of two push-pull substituted azobenzenes shown in Scheme 3.2 was also studied. Although it is possible for azobenzenes to isomerize by the same nitrogen-inversion mechanism as the N-benzylideneanilines [40], rotational isomerization via a highly dipolar activated complex 3.2 becomes predominant [41, 42] in polar solvents provided that the compound contains a strongly electron-donating dialkylamino group as in DNAB and DMNAB. 

An example of the effect of the presence of heteroatoms, especially those containing lone pairs of electrons, can be seen in comparing stilbene, which is colorless, with azobenzene, which is orange. The presence of the non-bonded electrons on the nitrogens in the azo compound allow for n tt transitions, which occur for the most part in the visible region of the spectrum (Fig. 3.5). 

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