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Open AccessArticle

Synthesis, Electrochemical and Spectroscopic Characterization of Selected Quinolinecarbaldehydes and Their Schiff Base Derivatives

1
Institute of Chemistry, University of Silesia in Katowice, ul. Szkolna 9, PL-40007 Katowice, Poland
2
Institute of Polymer and Dye Technology, Lodz University of Technology, Stefanowskiego 12/16, 90-924 Lodz, Poland
3
J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech Republic
4
Department of Chemistry and Industrial Chemistry, University of Pisa, Via Moruzzi 13, 56124 Pisa, Italy
5
Silesian Center for Education and Interdisciplinary Research, University of Silesia, Institute of Physics, 75 Pułku Piechoty 1a, 41-500 Chorzów, Poland
*
Authors to whom correspondence should be addressed.
Academic Editors: Sven Mangelinckx and Jacek Nycz
Molecules 2020, 25(9), 2053; https://doi.org/10.3390/molecules25092053
Received: 7 April 2020 / Revised: 24 April 2020 / Accepted: 26 April 2020 / Published: 28 April 2020
A new approach to the synthesis of selected quinolinecarbaldehydes with carbonyl groups located at C5 and/or in C7 positions is presented in this paper in conjunction with spectroscopic characterization of the products. The classical Reimer-Tiemann, Vilsmeier-Haack and Duff aldehyde synthesis methods were compared due to their importance. Computational studies were carried out to explain the preferred selectivity of the presented formylation transformations. A carbene insertion reaction based on Reimer-Tiemann methodology is presented for making 7-bromo-8-hydroxyquinoline-5-carbaldehyde. Additionally, Duff and Vilsmeier-Haack reactions were used in the double formylation of quinoline derivatives and their analogues benzo[h]quinolin-10-ol, 8-hydroxy-2-methylquinoline-5,7-dicarbaldehyde, 8-(dimethylamino) quinoline-5,7-dicarbaldehyde and 10-hydroxybenzo[h]quinoline-7,9-dicarbaldehyde. Four Schiff base derivatives of 2,6-diisopropylbenzenamine were prepared from selected quinoline-5-carbaldehydes and quinoline-7-carbaldehyde by an efficient synthesis protocol. Their properties have been characterized by a combination of several techniques: MS, HRMS, GC-MS, FTIR, electronic absorption spectroscopy and multinuclear NMR. The electrochemical properties of 8-hydroxy-quinoline-5-carbaldehyde, 6-(dimethylamino)quinoline-5-carbaldehyde and its methylated derivative were investigated, and a strong correlation between the chemical structure and obtained reduction and oxidation potentials was found. The presence of a methyl group facilitates oxidation. In contrast, the reduction potential of methylated compounds was more negative comparing to non-methylated structure. Calculations of frontier molecular orbitals supported the finding. The structures of 8-hydroxy-2-methylquinoline-5,7-dicarbaldehyde and four Schiff bases were determined by single-crystal X-ray diffraction measurements. View Full-Text
Keywords: vilsmeier-haack; reimer-tiemann; duff; aldehyde; aldazine; heterocyclic; cyclic voltammetry vilsmeier-haack; reimer-tiemann; duff; aldehyde; aldazine; heterocyclic; cyclic voltammetry
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MDPI and ACS Style

Wantulok, J.; Szala, M.; Quinto, A.; Nycz, J.E.; Giannarelli, S.; Sokolová, R.; Książek, M.; Kusz, J. Synthesis, Electrochemical and Spectroscopic Characterization of Selected Quinolinecarbaldehydes and Their Schiff Base Derivatives. Molecules 2020, 25, 2053.

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