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A novel Brönsted–Lewis acidic heteropoly organic–inorganic salt: preparation and catalysis for rosin dimerization
© Yuan et al. 2016
Received: 17 November 2015
Accepted: 4 April 2016
Published: 14 April 2016
A novel Brönsted–Lewis acidic heteropoly organic–inorganic salt has been prepared via the replacement of protons in neat phosphotungstic acid with both organic and metal cations. This hybrid catalyst, Sm0.33[TEAPS]2PW12O40, exhibited satisfactory performance in the dimerization of rosin to prepare polymerized rosin Under optimum conditions (15.0 g rosin and 5.0 g Sm0.33[TEAPS]2PW12O40 catalyst in 18.0 mL toluene at 90 °C for 10 h), a polymerized rosin product with a softening point of 120.1 °C was obtained. In addition, the Sm0.33[TEAPS]2PW12O40 catalyst maintains excellent catalytic performance over five recycles.
Polymerized rosin has a higher softening point, lighter color, and better stability than rosin, and is harder to oxidize. It is a key ingredient in oil paints, printing ink, adhesives, perfume, and more (Cheng et al. 1996; Chen 1992). The industrial preparation of polymerized rosin, employing aqueous mineral acids such as H2SO4 or ZnCl2/HCl, suffers from various shortcomings, including corrosion, pollution, and difficult recovery. Some environmentally friendly catalysts, such as solid superacids (Luo and Wu 1999; Gao et al. 2007), have been used to realize the clean polymerization of rosin. However, despite their superior separation, solid superacids exhibit insufficient recycling performance due to their uneven and vulnerable active components.
For the past few years, types of heteropoly organic salt catalytic materials have called attention for their potential water tolerance, acidity and self-separation performance (Leng et al. 2009a, b, 2012; Li et al. 2011, 2014; Shimizu et al. 2009; Sun et al. 2012; Zhou et al. 2014). It has been found that heteropoly anions with high charge numbers in these materials lead to higher melting points than conventional ionic liquids (Yuan et al. 2014). Furthermore, based on the high charge numbers of heteropoly anions, sulfated organic cations with Brönsted acidity and metal cations with Lewis acidity can act together as counterions to heteropoly anions, establishing novel Brönsted–Lewis acidic heteropoly organic–inorganic salts (Yu ST 2013). Herein, we report a heteropoly organic–inorganic catalyst, Sm0.33[TEAPS]2PW12O40, with Brönsted–Lewis acidity, which has different performances for melting point, solubility and acidity with both heteropoly compounds and ionic liquids. Moreover, the dimerization of rosin catalyzed by Sm0.33[TEAPS]2PW12O40 as a solid acid has been carried out to achieve an environmentally friendly process for polymerized rosin.
Materials and methods
Analytical grade H3PW12O40 was dried at 180 °C. All other chemicals were of analytical grade and used without further purification. The 1H-NMR spectra of the catalyst and intermediates were recorded with a 500 MHz Bruker spectrometer in D2O. FT-IR spectra for catalyst samples (the Py-IR sample was mixed with pyridine (2:1, v/v) for 24 h prior to measurement) on KBr discs were recorded on a Nicolet iS10 FT-IR instrument. Melting points were measured using a conventional method on an X-4 type micro melting point apparatus. TG analysis was performed with a NETZSCH-TG 209 F1 Libra instruments in dry N2 at a heating rate of 20 °C/min from 30 to 800 °C.
The acidity of the prepared catalysts was determined by potentiometric titration (Shi and Pan 2008; Vazquez et al. 2000). A mixture containing the sample (0.5 g) and acetonitrile (30 mL) was mixed at the stable potential before being titrated with n-C4H9NH2 solution (0.05 mol/L in acetonitrile). The initial and jump potential values were measured by a pH meter to identify the acid strength and total acid amount in catalyst samples.
Contrastive catalyst, [TEAPS]3PW12O40 and H2[TEAPS]PW12O40, were prepared according to the literature (Leng et al. 2009b). Analogously, equimolar triethylamine and 1,3-propanesultone (0.10 mol) were dissolved in 80 mL ethyl acetate and stirred at 50 °C for 24 h under nitrogen atmosphere. The obtained white precipitate, 3-(triethylammonio)propane sulfonate, was filtered, washed with ethyl acetate and dried at 100 °C for 6 h. Next, a solution of intermediate 3-(triethylammonio)propane sulfonate (0.008 mol) and Sm(NO3)3·6H2O (0.0013 mol) in water was dropped into another aqueous solution of H3PW12O40 (0.004 mol). The mixture was stirred at room temperature for 24 h, distilled to remove water, and washed with ethyl acetate. Finally, the obtained Sm0.33[TEAPS]2PW12O40 solid was dried in a vacuum at 80 °C for 6 h (Leng et al. 2009b; Ramesh Kumar et al. 2012). Catalyst Sm0.66[TEAPS]PW12O40 was prepared by a similar method to that outlined above, using alternative materials proportion.
Dimerization of rosin
In batch experiments, heteropoly organic–inorganic salt catalyst (5.0 g) was added to a round-bottomed flask contained toluene (18.0 mL) and dissolved rosin (15.0 g). The resulting reaction mixture was stirred vigorously at 90 °C for 10 h and then cooled to room temperature. The solid catalyst was removed by centrifugation and directly reused without further treatment. The reaction solution, from which the toluene solvent had been separated, was distilled under low pressure (2 mmHg) at 260–270 °C (system temperature) and 180–210 °C (steam outlet temperature) for 30 min to remove low softening point materials, such as rosinol and some unpolymerized rosin, and obtain the polymerized rosin product. The ring and ball softening points of the products were determined by SYD-2806G numerical control asphalt softening point tester.
Results and discussion
Characterization of hybrid catalysts
Properties of hybrid catalysts
Melting point (°C)
Solubility (25 °C)
Acid strength (mV)
Total acid amount (mmol/g)
Faint yellow/white crystal
Catalytic performances of Sm0.33[TEAPS]2PW12O40 in the dimerization of rosin
Catalytic dimerization performance of hybrid catalysts
Softening point (°C)
Acid value (mg/g)
Catalytic reusability of Sm0.33[TEAPS]2PW12O40 for the rosin dimerization
Catalyst recycle times
Softening point (°C)
Acid value (mg/g)
A novel heteropoly organic–inorganic salt with Brönsted–Lewis double acidity, Sm0.33[TEAPS]2PW12O40, was prepared via the replacement of protons in neat phosphotungstic acid with both organic cations containing sulfonic acid groups and metal Sm3+ cations. As a solid acid catalyst, this environmentally benign Brönsted–Lewis double acidic hybrid enables an effective catalytic performance in the dimerization of rosin to afford polymerized rosin products with a softening point above 115 °C. Moreover, the catalyst also exhibited reasonable reuseability, demonstrated by a five-run recycling test.
BY made the study desighs, did the data analysis, and drafted the manuscript. CXX, FLY, STY and JLZ participated in the design and coordination of the study and helped to draft the manuscript, XYY and XBC participated in the acquisition of data. All authors read and approved the final manuscript.
The financial support provided for this research by the “National Natural Science Foundation of China” (31470595, 31270615 and 21106074), “Opening Foundation of Beijing National Laboratory for Molecular Sciences” (20140141) and “The Taishan Scholar Program of Shandong” is gratefully acknowledged.
The authors declare that they have no competing interests.
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