Journal
SYNTHETIC METALS
Volume 159, Issue 5-6, Pages 445-455Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.synthmet.2008.11.002
Keywords
Polyaniline; Phenazine; Polyazane; Boyland-Sims rearrangement
Funding
- University of Texas at Dallas
- University of Massachusetts Lowell
- Nanomanufacturing Center of Excellence (NCOE)
- Center for High-rate Nanomanufacturing (CHN), NSF [0425826]
- Center for Advanced Materials
- Div Of Engineering Education and Centers
- Directorate For Engineering [0425826] Funding Source: National Science Foundation
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Chemical oxidative polymerization of aniline using peroxydisulfate oxidant in aqueous pH 2.5-10.0 buffers yields electrically insulating brown powders that are believed to be mixtures of Michael-type adducts of benzoquinone monoimine and aniline at various stages of hydrolysis. A spectroscopically similar product is formed when solid 1,4-benzoquinone is added to an aqueous solution of aniline at room temperature in the absence of peroxydisulfate. This suggests that the peroxydisulfate oxidant in the aniline/S2O82- system provides a pathway for the formation of benzoquinone monoimine as an intermediate. Benzoquinone monoimine intermediate could be formed as a result of a Boyland-Sims rearrangement of aniline proceeding via the intermediacy of p-aminophenyl sulfate. Benzoquinone monoimine undergoes a series of conjugate 1,4-Michael-type addition/reoxidation/coupling steps with aniline or p-aminophenyl sulfate yielding the oligoaniline product. The precipitate that is isolated is also in the midst of two simultaneous pH dependent hydrolysis reactions: (i) hydrolysis of the imine groups to quinone, and (ii) hydrolysis of arylsulfates to phenols. The ratio of hydrolysis in each case was determined by the C/N ratio and sulfur elemental analysis values yielding analytical data that is consistent with experimentally determined values and also with our proposed reaction scheme. These findings offer a rationale for the high C/N ratios (> 6.0) frequently observed in these systems while tracing the genesis of the residual sulfur in the product to unhydrolyzed arylsulfate. The oligoaniline product has previously been reported to have a novel poly-aza structure consisting of continuously linked -N-N-N- bonds, and alternately also reported to consist of phenazine-type linkages. This study is consistent with the latter and describes a pathway to phenazine coupling through a second and third stage hydrolysis of the arylsulfate and reoxidation with peroxydisulfate. There is no pathway for the formation of linear -N-N-N- linkages in the aniline/benzoquinone adduct and the striking similarity between its spectroscopic properties and the aniline/S2O82- adduct suggests that it is nota preferred pathway under these experimental conditions. (C) 2008 Elsevier B.V. All rights reserved.
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