Reversible capture and release of aromatic amines by vicinal tricarbonyl compound
Graphical abstract
Introduction
Vicinal tricarbonyl compounds, such as alloxan, 1,2,3-indanetrione (dehydrate form of ninhydrin), and dehydroascorbic acid (oxidative form of Vitamin C), are defined as compounds containing three consecutive carbonyl groups, and show highly electrophilic reactivity due to the electron-poor central carbonyl group.1, 2 One of the intriguing properties of vicinal tricarbonyl compounds is high reactivity to various nucleophiles. For instance, addition of vicinal tricarbonyl compounds and water, alcohol, or amine afford gem-diol, hemiketal, or hemiaminal, respectively (Scheme 1). Because these reactions proceed without any catalysts, vicinal tricarbonyl compounds are usually obtained as their hydrated form. These hydrates can be dehydrated by heating under vacuum,3, 4 sublimation,4, 5 distillation,6, 7, 8 crystallization,7 azeotropic removal of water,8 and utilization of dehydrating agents5, 8, 9 to afford the free vicinal tricarbonyls.
To date, we have investigated the reactivity of tricarbonyl compounds to water or alcohols in detail, and exploited the reactions to develop functional network materials. We have synthesized polystyrene derivatives containing vicinal tricarbonyl moieties in its side chain, and confirmed that water and alcohols added to the vicinal tricarbonyl polymer in a reversible manner.10 Based on the reaction, we have designed and synthesized a reversible network formation and dissociation system using the vicinal tricarbonyl polymer and 1,6-hexanediol11 or poly(ethylene glycol).12 Moreover, we have also reported the synthesis of a bifunctional vicinal tricarbonyl compound (bistriketone) and reversible crosslinking and decrosslinking systems of commercially available alcoholic polymers, namely, poly(2-hydroxyethyl methacrylate) and poly(vinyl alcohol), using bistriketone as a crosslinker.13 Thus, exploiting a new crosslinking unit plays an important role in developing functional networked materials.
As mentioned above, vicinal tricarbonyl groups can also undergo the addition of amines to the central carbonyl group. Previously reported methods for preparing hemiaminals of vicinal tricarbonyl compounds include the addition of amines,14, 15 imine,16 or amide17, 18 to vicinal tricarbonyl compounds. However, there was no report on reversibility of neither their hemiaminal formation nor their regeneration of vicinal tricarbonyl compounds, to the best of our knowledge, since most of the works focused on developing synthetic methods for natural products. These facts prompted us to construct novel, reversible capture and release system of amines by vicinal tricarbonyl compounds (Scheme 1). Herein, we describe our investigation on reversible capture and release behavior of aromatic amines by vicinal tricarbonyl compounds.
Section snippets
Results and discussion
First, we investigated capture and release behavior of amines by diphenylpropanetrione (DPPT) by 1H NMR (Fig. 1). The 1H NMR spectrum of a chloroform-d (CDCl3) solution of an equimolar mixture of DPPT and p-toluidine (0.1 M each) 10 min after mixing showed characteristic peaks at 8.01, 7.46, and 7.32 ppm as well as 2.18 ppm due to the protons of p-toluidine-adduct of DPPT (DPPT−p-toluidine). Fig. 2 shows the time dependence of conversion of DPPT in the addition of p-toluidine determined by 1H
Conclusion
The reversible capture and release behavior of the aromatic amines by diphenylpropanetrione was investigated in detail. The capture of the amines by DPPT proceeded smoothly to provide the aromatic amine adducts of DPPT (DPPT−amine adducts). Since addition reactions of DPPT and the aromatic amines were reversible, DPPT−amine adducts exist in fast equilibrium with DPPT and the amines in solution. Furthermore, we succeeded in the recovery of DPPT from DPPT−amine adducts by washing a solution of
General information
Chloroform and chloroform-d (CDCl3) were distilled over molecular sieves 4A (MS 4A). Dichloromethane and aniline were distilled over CaH2. n-Hexane and diethyl ether were dried over MS 4A. Tetrahydrofuran (THF) was distilled over sodium benzophenone ketyl. p-Toluidine, p-chloroaniline, p-nitroaniline, 4,4′-methylenedianiline, acetic acid (Wako), p-anisidine, o-toluidine, 3,5-xylidine, 2,4,6-trimethylaniline, diphenylamine (TCI) were purchased and used without further purification.
Acknowledgements
This work was supported by JSPS KAKENHI grant number 25288060.
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