A method was established to monitor organic reactions by micellar capillary electrokinetic chromatography (MEKC). After optimizing conditions such as the composition of the solvents, the surfactant, and the apparent pH (pH*) of the system, the method was utilized to analyze the reaction of glycidyl methacrylate (GMA) and allyl amine. The main products were identified in the electropherograms. The reaction procedure was monitored in real time. This method was found to have common applicability, being able to separate and detect nonaqueous soluble, nonionic, and low-UV-Vis absorbance compounds. It provides a rapid and low-cost way to understand organic reactions and to direct synthesis works.
Capillary electrophoresis (CE) is a rapid and high-performance method of separation and analysis [
It is very important to analyze the products of an organic reaction, as well as to monitor the related kinetics or reaction procedure. The related methods are mainly focused on elemental analysis, nuclear magnetic resonance (NMR), mass spectrometry (MS), infrared radiation (IR), and ultraviolet visible (UV-Vis) spectrometry. Many of these methods are usually obstructed by the limited purification of the products from complex reactions.
A chromatographic method (gas or liquid) can be used to simultaneously separate and detect complex samples. It enables the analysis and monitoring of organic reactions in real time [
In this paper, we give an example to explore the possibility to establish a universal method to study organic reactions by MEKC. Most of the compounds involved in an organic reaction, neutral or charged, water soluble, or insoluble, could be found in the electropherograms. The changing of relative peak areas of both the reactants and the products was used to monitor the reaction process.
Allyl amine was purchased from Haopeng Chemical Plant (Jinan, Shandong, China). GMA was purchased from Sigma. Cetyltrimethyl ammonium bromide (CTAB) was purchased from Lingfeng Chemical Reagents Co., Ltd (Shanghai, China). Imidazole was purchased from Sinopharm Chemical Reagents Co., Ltd (Shanghai, China). Other reagents were of analytical grade.
GMA and allyl amine (either 10
Capillary electrophoresis was carried out on a TriSepTM-2100 system (Unimicro Anal Tech Co, Shanghai, China). The capillary (100 um i.d., 360
The reaction of GMA and allyl amine was originally considered for the preparation of a multifunctionality monomer with high reactivity like a methacrylate. As showed in Figure
The reaction products of glycidyl methacrylate and allyl amine.
The pH* of the solution can obviously change the electroosmotic flow, as well as the charged status of the ionic analytes. The two main products of the reaction are basic compounds. Phosphorous acid (1 mol/L) was used to adjust the pH* of the running buffer. To overall compromise the resolution, resolved peak number, and total separation time, the pH* of the buffer was fixed at 6.50. Figure
The effect of pH*s on the separation of the reaction mixture. Buffer: Imidazole 15 mM, CTAB 35 mM in methanol/acetonitrile 65/35 (v/v). pH* (adjusted with H3PO3): (a) 6.01, (b) 6.50, and (c) 7.02. Voltage: 20 kV. Detection wavelength: 214 nm. Injection: 5 kV/5 sec. Capillary: 50
One of the reactants, allyl amine, is water soluble and the other, GMA. is insoluble in water. As to the products, their solubility could vary in a wide range. To dissolve all the reactants and products, solvents like methanol, acetonitrile, and their mixtures were tried. Finally, the mixture of methanol/acetonitrile (65 : 35 v/v) was used to run the electrophoresis. In this case, it became a nonaqueous mode of CE [
CTAB was used to form a micelle in which neutral compounds can be separated. On the other hand, CTAB can affect the electroosmotic flow (EOF) in CE, by absorption on the inner wall of the capillary and neutralizing the deprotonated silanol groups. Hence, increasing the concentration of CTAB could decrease the EOF and prolong the total separation time. Finally, CTAB was used in the concentration of 35 mmol/L.
The electropherograms indicating the reaction process are showed in Figure
Reaction process of GMA and allyl amine. Time of reaction: (a) 30 min, (b) 90 min, (c) 150 min, and (d) 12 h. Peaks: (1) allyl amine, (2) GMA, (3) thiourea, (4) 2-hydroxyl-3-allylamino-propyl methacrylamide (product I in Figure
The reaction can be elucidated from the variation of the area ratios of the compounds (to that of thiourea). Figure
The peak area ratios (to that of thiourea) varied versus time. (a) GMA, (b) compound I, and (c) compound II. Electrophoresis conditions are the same as in Figure
A useful method based on nonaqueous MEKC was developed to analyze organic reactions. An example was given to identify the various products of the reaction of GMA and allyl amine and to monitor the reaction process. It was found both neutral and charged, low UV-Vis absorbance compounds could be separated and identified with such an applicative method. With the popularization of CE in analytical fields, this method enables us to analyze and monitor organic reactions in an on-line, real-time, and low-cost method.
This work was financially supported by SRF (Ministry of Education, China) and Key Laboratory of Separation Sciences for Analytical Chemistry (KL1005, Dalian Institute of Chemical Physics, Chinese Academy of Sciences).