<b>Investigation of the Kinetics and Mechanism of the Anodic Oxidation of Aniline in Aqueous Sulfuric Acid Solution at a Platinum Electrode</b>

Mohilner, David M.; Adams, Ralph N.; Argersinger, William J.

doi:10.1021/ja00878a003

Cited by 417 publications

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“…The pretreated Pt electrode was set in the spectroelectrochemical cell into which a given volume of aqueous HClO 4 or H 2 SO 4 solution containing aniline was poured, left alone for 30 min, and then thrust against the optical window to form a thin electrolyte layer. The potential was swept from an open-circuit value to +0.50 V (there is no oxidation of aniline).…”

Section: Methodsmentioning

confidence: 99%

“…2,3 According to the reaction scheme proposed by Mohilner et al, polymerization starts by the oxidation of non-protonated aniline to radical cationic species, and proceeds through coupling with another radical; these reactions are accompanied by the release of protons to eliminate the generated positive charges. 4 This suggests that the acidity at the polymer/solution interface increases during the course of aniline oxidation, but the effect of accumulated protons on the rate of polymerization is not determined. Furthermore, side reactions, such as degradation of the polymer, are not negligible during prolonged polymerization.…”

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In Situ Observation of Electrochemical Formation and Degradation Processes of Polyaniline by Fourier-Transform Infrared Spectroscopy

1999

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Polyaniline (PAn) is an electrically conducting polymer that can be easily prepared by the chemical and electrochemical oxidation of aniline, and shows excellent stability under ambient conditions. Electrochemical synthesis is generally carried out on metal electrodes in aqueous acidic solutions, such as HClO 4 , HCl and H 2 SO 4 , using potentiostatic, galvanostatic and potential cycling methods. A large number of studies on the redox process of PAn have been performed by means of electrochemical and optical techniques, revealing that electron transfer causes the migration of electrolyte ions into or out of the polymer film. 1 However, the scheme of electropolymerization of aniline, involving the charge-compensation manner, is not well understood. A film prepared from HClO 4 is known to be denser than that from H 2 SO 4 , suggesting that the electrolyte anion plays an important role in the polymerization of aniline. 2,3 According to the reaction scheme proposed by Mohilner et al., polymerization starts by the oxidation of non-protonated aniline to radical cationic species, and proceeds through coupling with another radical; these reactions are accompanied by the release of protons to eliminate the generated positive charges. 4 This suggests that the acidity at the polymer/solution interface increases during the course of aniline oxidation, but the effect of accumulated protons on the rate of polymerization is not determined. Furthermore, side reactions, such as degradation of the polymer, are not negligible during prolonged polymerization. 5 An in situ spectroelectrochemical method is useful to study such unclear problems.In the present study, in situ FTIR spectroscopy was applied to the electrochemical polymerization of aniline, and the growing polymer and polymer/solution interface were investigated on the molecular level. In situ FTIR spectroscopy has proven to be fruitful for studies on the metal/solution interface 6 and an electroactive film.7 An advantage of this technique when used in the latter system is that it allows a simultaneous determination of the polymer structure and movement of electrolyte species through the film. ExperimentalAll chemicals were of reagent grade and used as received. Sulfuric and perchloric acid solutions used as the electrolytes were prepared with those chemicals and doubly distilled water, and higher pH values were adjusted by adding a concentrated NaOH solution.The FTIR spectrometer used was a Shimadzu FTIR 8100M equipped with an external-reflection unit and a HgCdTe (MCT) detector cooled with liquid nitrogen. The spectroelectrochemical cell was similar to that described elsewhere. 8 A flat CaF 2 disk was used as the IR transparent window, and the angle of incidence on the CaF 2 surface was 70˚. Spectroelectrochemical experiments were carried out with a Pt disk (area=0.50 cm 2 ) substrate. The Pt surface was polished to a mirror finish with 0.3 µm alumina paste and sonicated for 10 The electrochemical polymerization of aniline on a platinum electrode in aqueous HClO4 and H...

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Section: Methodsmentioning

confidence: 99%

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confidence: 99%

In Situ Observation of Electrochemical Formation and Degradation Processes of Polyaniline by Fourier-Transform Infrared Spectroscopy

1999

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“…Segundo alguns autores, a primeira etapa de polimerização envolve a oxidação da anilina formando o cátion radical, sendo as etapas pos-teriores, de acoplamento, fortemente dependentes do pH 12 . Em condições ácidas prevalece o acoplamento cabeça-cauda, que favorece a formação do dímero predominante no processo de polimerização da PAni condutora, p-aminodifenilamina (ADPA) 22,23 . À medida que o pH do sistema aumenta, tornando-se neutro, observam-se evidên-cias da formação de ligações N-N, sugerindo o acoplamento cabeça-cabeça 23 .…”

Section: Introductionunclassified

Tratamento dos resíduos gerados na síntese de polianilina em escala pré-piloto

Sousa¹,

Araújo²,

Freitas³

et al. 2003

Quím. Nova

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Recebido em 6/1/03; aceito em 29/4/03 TREATMENT OF THE RESIDUES GENERATED BY POLYANILINE SYNTHESIS IN PRE-PILOT SCALE. Polyaniline (PAni) is one of the most studied conducting polymer. It can be synthesized by two methods: electrochemical or chemical oxidation. The chemical oxidation is more adequate to produce large quantities of polymer. Regardless of the synthesis scale, the treatment of the residues before its final destination is very important and necessary because it contains toxic aniline derivatives (carcinogens in some cases), acids and inorganic salts, both with low toxicity. In this work we discuss the methods used to treat these residues and to eliminate and discard the toxic substances. These were extracted from the reaction residues by using activated coal and the pH of the residue was neutralized.Keywords: polyaniline; residues; coal. INTRODUÇÃOO tratamento de resíduos químicos gerados nos laboratórios das instituições de ensino e pesquisa no Brasil é um assunto cada vez mais discutido entre a comunidade acadêmica 1 . Nas universidades, não são raros os casos em que os alunos de graduação (dos diversos cursos que se utilizam da Química), em suas práticas laboratoriais, não são devidamente instruídos sobre a geração de resíduos e seu devido tratamento antes do descarte. Assim, os resíduos provenientes de sínteses químicas e testes analíticos acabam sendo descartados diretamente no sistema de esgoto sanitário, resultando em contaminação ambiental. Em outros casos, diferentes resíduos são armazenados em um mesmo recipiente sem identificação, o que dificulta sua caracterização 1 , e não são tomadas iniciativas quanto ao seu tratamento e destino final. Felizmente, a crescente preocupação com o meio ambiente tem despertado o interesse de alguns Institutos de Química em criar programas de gerenciamento dos resíduos gerados nos laboratórios de ensino e pesquisa 1-3 , que podem servir de modelo para aqueles que ainda não dispõem destes programas. Dentre as medidas tomadas estão: minimização dos resíduos produzidos, cadastramento e segregação dos diferentes resíduos a serem estocados, tratamento antes da destinação final, e a recuperação daqueles que possam ser reutilizados 1-3 . Tradicionalmente, sempre que se deseja traçar uma estratégia de síntese em laboratório ou em escala piloto, seja nas universidades ou indústrias, a maior parte dos esforços são concentrados em se obter uma rota sintética que vise minimizar os custos e maximizar o rendimento do produto desejado. Assim, os subprodutos das reações, ou resíduos, só recebem a devida atenção depois de constatados os danos ambientais. Portanto, quando se pretende desenvolver um novo experimento, que envolva substâncias químicas, é fundamental que no seu planejamento sejam avaliadas a toxicidade e a reatividade dos reagentes e de todos os possíveis subprodutos da síntese. Deve-se considerar também, se estes reagentes e subprodutos não atuam como precursores de substâncias potencialmente tóxicas quando expostos no meio ambiente. Desta maneira, é desejável ...

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“…In 1962 Mohilner, Adams and Argersinger reinvestigated the mechanism of the electrooxidation of aniline in aqueous sulfuric acid solution at a platinum electrode. They proposed a free radical mechanism, and wrote that "the final product of this electrode reaction is primarily the octamer emeraldine, or a very similar compound" [18].…”

Section: Historical Backgroundmentioning

confidence: 99%

Synthesis; Redox behaviour; Composites; Sensors; Biosensors; Supercapacitors; Electrocatalysis

Inzelt

2017

J. Electrochem. Sci. Eng.

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Investigation of the Kinetics and Mechanism of the Anodic Oxidation of Aniline in Aqueous Sulfuric Acid Solution at a Platinum Electrode

Cited by 417 publications

References 0 publications

In Situ Observation of Electrochemical Formation and Degradation Processes of Polyaniline by Fourier-Transform Infrared Spectroscopy

In Situ Observation of Electrochemical Formation and Degradation Processes of Polyaniline by Fourier-Transform Infrared Spectroscopy

Tratamento dos resíduos gerados na síntese de polianilina em escala pré-piloto

Synthesis; Redox behaviour; Composites; Sensors; Biosensors; Supercapacitors; Electrocatalysis

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