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Oxidation of 4-chloroaniline studied by on-line electrochemistry electrospray ionization mass spectrometry
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
2009 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 81, no 13, 5180-5187 p.Article in journal (Refereed) Published
Abstract [en]

The oxidation of 4-chloroaniline (4-CA) has been studied by electrochemistry (EC) coupled on-line with electrospray ionization mass spectrometry (ESI-MS) using two electrochemical flow cells of different design. The experimental results, which generally verify previously suggested oxidation pathways for 4-CA, also indicate the presence of a so far unrecognized comproportionation reaction. The oxidation of 4-CA (m/z 128.2) was found to give rise to the formation of both an oxidized dimer, 4-[(4-chlorophenyl)imino]-2,5-cyclohexadien-1-imine (m/z 217.2) and a reduced dimer, 4-amino-4’-chlorodiphenylamine (m/z 219.2), in addition to a dimer intermediate (m/z 253.2). This unexpected formation of the reduced dimer is shown to stem from a comproportionation reaction involving 4-CA and the oxidized dimer. The presence of the latter reaction was clearly seen by comparing results obtained with two thin-layer flow cells, both with conversion efficiencies of 50% but of different design, with respect to the influence of the counter electrode reaction on the reaction at the working electrode. The experimental results demonstrate that the formation of the reduced dimer is favored by a decrease in the local pH in the flow cell and the influence of the pH on the oxidation of 4-CA was also investigated in the pH range between 2.0 and 6.0 using off-line voltammetry. It is concluded that EC/ESI-MS is a powerful tool for the study of the present type of reactions and that studies on reaction pathways are best carried out with thin-layer flow cells having conversion efficiencies smaller than 100% as this facilitates the detection of reaction intermediates. Comproportionation reactions, similar to the reaction present in the 4-CA system, can also be expected to be present during the formation of conducting polymers such as polyaniline and polypyrrole.

Place, publisher, year, edition, pages
2009. Vol. 81, no 13, 5180-5187 p.
Keyword [en]
4-chloroaniline, oxidation, electrochemistry, electrospray ionization mass spectrometry, reaction pathway, (p-chlorophenyl)aniline
National Category
Chemical Sciences
Research subject
Analytical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-99325DOI: 10.1021/ac802563fISI: 000267609500013PubMedID: 19563209OAI: oai:DiVA.org:uu-99325DiVA: diva2:207621
Available from: 2009-03-12 Created: 2009-03-12 Last updated: 2017-12-13Bibliographically approved
In thesis
1. On-line Electrochemistry Electrospray Ionisation Mass Spectrometry: Method Development and Applications
Open this publication in new window or tab >>On-line Electrochemistry Electrospray Ionisation Mass Spectrometry: Method Development and Applications
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with studies of on-line electrochemistry electrospray ionisation mass spectrometry (EC/ESI-MS). It is shown that the use of EC/ESI-MS demands optimal coupling characteristics.

Pre-concentration and desalting, due to matrix exchange, were demonstrated for the model substance 1-hexanethiol in an EC/ESI-MS setup. The setup was also used for investigations of the oxidation states of the manganese complex [Mn2(bpmp)(µ-OAc)2][ClO4], where bpmp is a 2,6-bis[[N,N-di(2-pyridylmethyl)amino]methyl]-4-methylphenol compound. The manganese complex, which is relevant to artificial photosynthesis, was found to be a good model compound for the EC/ESI-MS studies, thanks to its many oxidation states. For the first time, the presence of the Mn(III,IV) state of the manganese complex was demonstrated in the studies.

During the experimental work, the importance of the electrode positioning within the electrochemical cell was investigated. Different EC cell configurations were studied using the manganese complex as a model substance. It was clearly shown that the EC cell design influences the distribution between the peaks in the mass spectra - not only for manganese complexes and Olsalazine but also for 4-chloroaniline.

A previously unknown comproportionation reaction was found for 4-chloroaniline involving the oxidised dimer, 4-[(4-chlorophenyl)imino]-2,5-cyclohexadien-1-imine. This reaction explained the unexpected presence of the signal due to the reduced dimer, 4-amino-4'-chlorodiphenylamine, in the mass spectra.

Furthermore, it was shown that EC/ESI-MS was successful in conjunction with miniaturised gold wire electrodes in a PDMS chip within which dopamine was oxidised with a conversion efficiency of 30%. The oxidation products of dopamine were detected after 0.6-1.2 seconds for 1.0 and 0.5 µl/min, respectively. The combination of electrochemically controlled solid-phase extraction (EC-SPE) with ESI-MS was found to be less straightforward than detecting anions pre-concentrated on a polypyrrole coated electrode with EC-SPE/ICP-MS.

The on-line combination of liquid chromatography with EC/ESI-MS/MS for studying antioxidants in yellow onion extracts was shown to be fast and a relatively easy complement to classical antioxidant activity determinations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 78 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 622
National Category
Chemical Sciences
Research subject
Analytical Chemistry
Identifiers
urn:nbn:se:uu:diva-99329 (URN)978-91-554-7459-1 (ISBN)
Public defence
2009-04-24, BMC, B42, Husargatan 3, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2009-04-02 Created: 2009-03-12 Last updated: 2009-04-06Bibliographically approved

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Zettersten, CamillaSjöberg, Per J. R.

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