1.2- Diamines, reaction with benzoquinones

Condensation of benzene-1,2-diamine (25) with 1,2-benzoquinones 26 under various reaction conditions affords phenazines 27 directly. 1,2-Benzoquinones should be prepared in situ to avoid selfcondensalion (see Houben-Weyl, Vol. 7/3 b, p 1). A solvent effect has been observed when conducting this reaction in different solvents in methanol the reaction product is phenazine-2,3-diol and in diethyl ether predominantly phenazine is formed. ... 

The reaction of 1,2-benzoquinones with 1,2-diamines gives p3zrazine derivatives, but examples since 1980 are very limited. For example, reaction of the diamine 89 with 1,2-benzoquinone gives the 2,3-di-p-tolylquinoxaline 90 (equation (10)) (85JA1501). In a similar way, a... 

The reaction of o-diamines 7 with o-benzoquinone or cyclohexane-1,2-dione is used for des ping of the quinoxaline system in porphyrins (1996JCS(P1)2675). In this case, in contrast to the classical reaction of Hinsberg-Kerner there occurs quinoxahneannulation to which the diamine moiety belongs. 

The diamines are isoelectronic with hydroquinone (an eiectron donor) while the diimines are isoelectronic with p-benzoquinone (an electron acceptor). It was recently proposed that this built-in redox couple, which is pH-sensitive, is the source of charge carriers in the form of semiquinone radical cations which are generated upon protonation of the quinonediimine, whose accepting power is expected to increase on protonation. A subsequent perusal of the literature indicates that a similar idea was proposed many years ago. A key issue yet to be resolved is whether electron transfer from diamine to diimine is an inter- or intramolecular process. An alternative mechanism of carrier generation which involves spin unpairing of diimines (creating a pair of radical cations) has recently been proposed." Carrier transport is believed to occur via intermolecular redox reactions between radical cations and diamine and/or diimine units. 

Gebert et al. [52] have reported a synthesis of polyaniline using Schiff base chemistry. The reactions involve the condensation of para phenylene diamine with p-benzoquinone and can be written as (Scheme 12.9). The obtained polymer has a conductivity of 4 X 10 S m . ... 

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