General Papers
ARKIVOC 2016 (v) 327-337
A convenient method for the synthesis of 3,6-dihydroxybenzene-1,2,4,5-tetracarboxylic acid tetraalkyl esters and a study of their fluorescence properties Aswathy L. Balachandran, Vidya Sathi, Ani Deepthi,* and Chettiyam V. Suneesh Department of Chemistry, University of Kerala, Thiruvananthapuram 695581, Kerala, India E-mail:
[email protected] DOI: http://dx.doi.org/10.3998/ark.5550190.p009.843 Abstract A mild, efficient and simple method for the synthesis of 3,6-dihydroxy-1,2,4,5-tetracarboxylic tetraalkyl esters using cerium(IV) ammonium nitrate mediated oxidation of 1,3-acetone dicarboxylates has been developed. The detailed absorption and emission studies of the synthesized compounds reveal that these molecules have appreciable quantum yields and possess large Stokes shift values. Keywords: Pyromellitic dianhydride, 1,3,5-tricarbonyl compounds, cerium(IV) ammonium nitrate, quantum yield, Stokes shift
Introduction Among other methods,1 vapour phase oxidation of pyromellitic acid leads to the synthesis of pyromellitic dianhydride (PMDA) which in-turn is the chief raw material for the production of polyimides2 that are used in aircraft industry and cryogenics.3 Apart from the production of PMDA, pyromellitic acid has also been extensively used for the synthesis of Metal Organic Frameworks (MOFs)4 which has rich applications in gas storage, catalysis, luminescent sensing and separations.5 Conventional synthesis of pyromellitic acid from p-xylene involves an initial chloromethylation followed by oxidation of the resulting compound using organometallic catalysts.6-9 Modified methods for its synthesis using ionic liquids have also been reported.10 However, to the best of our knowledge, except for a few isolated early reports,11,12 further studies on pyromellitic acid derivatives with hydroxyl substituents in the 3,6-positions are unknown in the literature. In the aforementioned reports, von Pechmann and Hammond have used sodium wire and iodine for the synthesis of these compounds (Scheme 1). The method is both cumbersome and very low yielding. At the same time, 3,6-dihydroxybenzene-1,2,4,5-tetracarboxylates are the only direct source of 1,4-benzoquinone-2,3,5,6-tetracarboxylates which are strong electron-acceptors.12 Hydroquinone/quinone redox couples are the widely used electron transport cofactors in the
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