An Application of Chemical Oscillation: Distinguishing Two Isomers between Cyclohexane-1,3-dione and 1,4-cyclohexanedione
Graphical abstract
Introduction
Some chemical systems, being far from equilibrium, show nonlinear kinetic behaviors, such as periodic oscillations [1], chaos [2], wave propagation and pattern formation [3]. Among such nonlinear systems, periodic chemical oscillation not only exhibits the unique kinetic behaviors but it has also been used as unique tools in the analytical field. For example, some quantitive approaches based on oscillatory reaction have been developed for determination of analytes by their perturbation effects on oscillating system since 1978 when the pioneer work was established by Tichonova et al. Some succeeding developments in quantitive analysis include determination of irons (Ru3+, Ru4+, Hg2+), gases (CO, NO, Cl2) [4] analysis, and organic reagent analysis [5]. Strenuously, analysts utilized both the Belousov-Zhabotinsky (BZ) oscillating reaction and the Briggs-Rauscher (BR) oscillator, exploring the new domain where these two matrixes can be applied.
Like BZ oscillation which occurs in homogeneous solution, the BR system (an acidic solution of hydrogen peroxide, potassium iodate, malonic acid, and catalyst) exhibits typical periodic color changes from colorless to yellow to blue then to colorless with a starch indicator, making it an excellent demonstration in lab at its first emergence in history. Continuous studies on such reaction have revealed its complex mechanism, in which both the non-radical process and the radical process exist during oscillations [6]. Understanding on its unique dynamics has helped analysts utilize BR as a matrix to measure some antioxidants activities [7], [8], [9], [10], [11]. Antioxidant activities could be evaluated because antioxidants were found to function as free-radical scavengers to react with the radical intermediate in the BR system.
In our previous studies, we have shown that, some oscillating systems of BR type or BZ type can act as suitable matrixes in measurement of abundant of analytes, such as eugenol [12], Ag+ [13], pyrogallol [14],catechol [15],calcium pantothenate [16] and alizarin red [17]. Catalysts involved in these BR or BZ systems are macrocyclic complexes, [CuL](ClO4)2 or [NiL] (ClO4)2 (Scheme 1), where the ligand L in the complex is 5,7,7,12,14,14-hexemethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. The ligand of the complexes occupies the extended π-system, which ensures a high rate for reactions involving electron transfer at individual steps of the oscillating process [18]. This character makes these chemical oscillatory matrixes vulnerable to the external perturbations. As previous applications of chemical oscillation focus on the quantitative analysis, we report in this paper a novel qualitative method for distinguishing two positional isomers of cyclohexane-1,3-dione (1,3-CHD) and 1,4-cyclohexanedione (1,4-CHD) (Scheme 2) by utilizing their perturbation effects on such a catalyzed BR oscillation.
Some isomers are found tough getting separated and distinguished because they usually possess the same molecular weight, the same physical properties or even the same functional groups. In an attempt to distinguish the isomers, some instrumental methods like MS [19], GC–MS [20] and HPLC-NMR [21] have been employed. The mass spectrometry (MS) is based on the distribution of ions by mass-to-charge ratio and hence it can measure the mass of a molecule. But the method has difficulty in distinguishing isomers because the ion fragments come from two isomers may have the same mass-to-charge ratio and similar distribution. By coupling the high separation efficiency of gas chromatograph (GC) with high sensitivity of mass spectrum (MS), GC-MS method has the advantage of high sensitivity in distinguishing the isomers. But this technique does not work for some compounds with high boiling point because some molecules are prone to be decomposed at high operating temperature. Being insensitive to light and oxygen, the HPLC-NMR method possesses high separation and identification efficiency with high accuracy in structural analysis. However, one of its disadvantages is its low sensitivity. Another disadvantage is that it only works for small molecule but is not suitable for identification of macromolecular isomers. A new electrochemical method for distinguishing isomers is expected.
In this paper, an accomplishment for identification of two position isomers (1,3-CHD and 1,4-CHD) was achieved by using a Briggs−Rauscher oscillating reaction. The concentrations of 1,3-CHD and 1,4-CHD that can be distinguished is over the range from 9.0 × 10−4 to 8.0 × 10−3 M. Compared with our previous application of using BR reaction for quantitative measurement of analytes [12], [13], [14], [15], [16], [17], this electrochemical technonogy involving a BR reactor provieds a new rapid qualitative method in identification of two isomers (1,3-CHD and 1,4-CHD) with simpler equipment.
Section snippets
Apparatus
All chemicals used were of analytical reagent grade without further purification except for the catalyst [NiL](ClO4)2, which was synthesized according to a published procedure [22], [23] and identified by elemental analysis and IR spectrum. KIO3, malonic acid, H2O2 and sulfuric acid were obtained commercially from Sinopharm Chemical Reagent Co.,Ltd. Cyclohexane-1,3-dione (1,3-CHD) and 1,4-cyclohexanedione (1,4-CHD) were purchased from Shanghai Chemical Industry Development Co.,Ltd.
Action of distinguishing of two position isomers between 1,3-CHD and 1,4-CHD
In order to distinguish two position isomer, perturbation experiments were made by addition of the same amount of 1,3-CHD or 1,4-CHD into the BR system. We added 40 μL of 1.5 M of, 40 μL of 3.75 M of, or 80 μL of 3.75 M of 1,3-CHD solution into the BR system to make its concentration in the system reach 1.5 × 10−3 M, 3.75 × 10−3 M, or 7.5 × 10−3 M, respectively (Fig. 1. b,d and f). Also, we added 40 μL of 1.5 M of, 40 μL of 3.75 M of, or 80μL of 3.75 M of 1,4-CHD solution into the BR system to make its
Conclusions
We demonstrated that, for the first time, a macrocyclic Ni(II) complex-catalyzed BR oscillator could be utilized as a suitable tool in electrochemically distinguishing two positional isomers of 1,3-CHD and 1,4-CHD. The different perturbation mechanisms of these two isomers on the BR system result in the difference in potentiometric oscillation profiles change, which could be employed in qualitative analysis. We revealed that, 1,3-CHD is oxidized into carboxylic acid by radical IO2, whereas
Acknowledgment
The authors gratefully acknowledge funding of this work by the National Science Foundation of China (21171002).
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2021, Microchemical JournalCitation Excerpt :Recently, our group has successfully explored a new field in the qualitative assay of organic analytes using a BR system [31–36] based on their perturbation responses. Briefly, by perturbating such an oscillating system with analytes, we have shown that two aliphatic isomers (α-ketoglutaric from β-ketoglutaric acid) could be successfully identified in 2015 [31], while another two cyclohexanedione isomers (cyclohexane-1,3-dione from 1,4-cyclohexanedione) could be recognized in 2016 [32]. In order to explore the new domain that the oscillating system could be applied, we manage to utilize a BR system in identification of different inorganic species (metal ions) from each other in this paper.
Identification of two aromatic isomers between 3- and 4-hydroxy benzoic acid by their perturbation on the potential oscillations of a Belousov-Zhabotinsky system
2020, Arabian Journal of ChemistryCitation Excerpt :In order to widen the application of oscillating chemical system, we utilized chemical oscillators for the identification of isomers of a compound. Previously, our group successfully utilized BR chemical oscillator for the identification of two aliphatic isomers (α-ketoglutaric from β ketoglutaric acid) in 2015 (Zhang et al., 2015), and another two cyclohexane isomers (cyclohexane-1,3-dione from 1,4-cyclohexanedione) in 2016 (Chen et al., 2016). In order to find out if some types of chemical oscillator rather than BR type could be utilized for identifying other types of isomers, we consider the BZ oscillator for identification of two aromatic isomers.
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2018, Journal of Electroanalytical ChemistryCitation Excerpt :In 2015, a novel method for the identification of two aliphatic position isomers between α-ketoglutaric acid and β-ketoglutaric acid by their different was presented [34]. Similarly, BR oscillator was used to distinguish cyclohexanedione isomers (cyclohexane‑1,3‑dione from 1,4‑cyclohexanedione) [35] and disubstituted or polysubstituted benzonic isomers (2‑ and 3‑hydroxy benzonic acid, ortho and para vanillin) [36, 37]. So far, BZ oscillator was only utilized for disubstituted benzonic isomers (3‑ and 4‑hydroxy benzoic acid) [37].
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2017, Journal of Electroanalytical ChemistryCitation Excerpt :The BR system is not only limited for the determination of compounds or species but it has a vast potential applications such as waves production, patterns formations, chemical chaos etc. Recently, our group has successfully identified aliphatic isomers (α-ketoglutaric from β ketoglutaric acid) [33] and cyclohexane isomers (cyclohexane-1,3-dione from 1,4-cyclohexanedione) [34] based on BR oscillator. In order to extend the application of BR oscillator, we consider identifying aromatic isomers.