1.2.4.5- Tetraaminobenzene

One method of solving the kinetics dilemma is well known in coordination chemistry that is, start with a labile metal ion and render it inert during the course of the synthetic reaction. We have accomplished this in the case of zirconium(IV) by starting with tetrakis(salicylaldehydo)zirconium(IV), which is quite labile, and polymerization with 1,2,4,5-tetraaminobenzene in a Schiff-base condensation reaction in situ (6). The polymeric product contains a "double-headed" quadridentate ligand, which is much more inert to substitution. However, 1,2,4,5-tetraaminobenzene has become very expensive. Therefore, the synthesis of a zirconium polymer with 3,3, 4,4 -tetraaminobiphenyl (commercially 3,3 -diami nobenzidine) with zirconium salicylaldehyde, Zr(sal)4 (7) has been undertaken as shown below ... 

The pentacyclic bitropone 166 is prepared by the condensation of p-tropoquinone (137) and 1,2,4,5-tetraaminobenzene (88CL175 89CL1719). 

Note The 1,2,4,5-tetraaminobenzenes are sensitive to atmospheric oxygen and easily oxidise to mixtures containing p-benzoquinonediimines. The corresponding p-benzoquinone-diimines can be synthesised in high yield by standard procedures. 

A new quality in ladder polymer synthesis via multifunctional polycondensation was reached in the late 1960s when poly(benzimidazobenzo-phenanthroline) (BBL) 12 was prepared by Arnold and van Deusen [21 -24]. The polymer was synthesized from naphthalene-l,4,5,8-tetracarboxylic acid dianhydride (11) and 1,2,4,5-tetraaminobenzene (la) in strong acidic media (polyphosphoric acid, sulfuric acid). BBL is completely soluble in concentratal sulfuric acid or methanesulfonic add and is processible into durable films and... 

Sdieme 15e Two-stage polybenzimidazole thesis from 1,2,4,5-tetraaminobenzene and aromatic dialdehydes... 

Other group of ionomers for PEM fuel cells are based on polymers, such as poly [2,2 -(m-phenylene)-5,5 -bibenzimidazole] (m-PBI), obtained by polymerization of 3,3 -diaminobenzidine, 1,2,4,5-tetraaminobenzene and a variety of aromatic diphenyl dicarboxylates [189], whose structure is shown in Fig. 6.10. This non-ionic polymer becomes a proton conductor when doped with a strong acid such as sulphuric or phosphoric acid. 

Sulfonated polybenzoimidazole (sPBI) membranes have also been prepared by poly condensation of 2-sulphoterephthalic acid with 1,2,4,5-tetraaminobenzene tetrahydrochloride [193] or by grafting alkyl or aryl sulfonates on to the imidazole ring [194]. ABPBI was sulphonated by immersion in sulfuric acid followed by heat treatment at 450 °C [195]. Other methods of sulphonation have been reviewed by Asensio et al. [196], along with a detailed description of the properties of PBI blends with sulfonated and non-sulfonated polymers, and block PBI copolymers. 

On the other hand, some of the monomers are potentially dangerous. For example, 3,3, 4,4 -biphenyltetramine tetrahydrochloride is suspected of causing genetic defects and may cause cancer. 3,3 -Diaminobenzidine has carcinogenicity for the rat and is tumorigenic. 1,2,4,5-Tetraaminobenzene tetrahydrochloride and 2,6-Dicarboxypyridine cause skin irritation and serious eye irritation. 

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