Ultrasound-assisted fast preparation of low molecular weight fucosylated chondroitin sulfate with antitumor activity

Progress in Reaction Kinetics and Mechanism, 2018, 43(3–4), 254–261 https://doi.org/10.3184/146867818X15319903829173 Paper: 1700643

Nanopowder-supported ultra-low content Co–Rh bimetallic catalysts for hydroformylation of monoformyltricyclodecenes to value-added fine chemicals Chengyang Lia,b, Libo Zhanga,b, Yubo Maa and Tianfu Wanga* aLaboratory of Environmental Science and Technology, The Xinjiang Technical Institute of

Physics & Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi 830011, P.R. China bUniversity of Chinese Academy of Sciences, Beijing 100049, P.R. China

*E-mail: [email protected]

ABSTRACT The hydroformylation of monoformyltricyclodecenes (MFTD) to diformyltricyclodecanes (DFTD) was studied systematically. A series of 0.006 wt% Rh–0.006 wt% Co catalysts supported on commercially available nanopowders such as Al2O3, ZnO, TiO2 and CeO2 was prepared by the incipient wetness method and used to catalyse the hydroformylation of MFTD to DFTD. The 0.006 wt% Rh–0.006 wt% Co/ZnO catalyst showed the highest catalytic performance among the catalysts investigated, thus 41.8% DFTD yield with 100% DFTD selectivity could be achieved. This suggested that there may be a key role of the carrier on the catalytic performance in MFTD hydroformylation. Furthermore, the kinetic profiles for MFTD hydroformylation over the 0.006 wt% Rh–0.030 wt% Co/ZnO catalyst have been examined systematically to explore the effect of reaction temperature on the catalytic performance. These results collectively suggested that a particular reaction temperature might benefit MFTD hydroformylation. There may be some agglomeration of the active sites at higher reaction temperatures. KEYWORDS: monoformyltricyclodecenes, diformyltricyclodecanes, hydroformylation, nanopowder ZnO 1. INTRODUCTION Hydroformylation of olefins to their corresponding aldehydes is one of the most important chemical industrial processes [1]. Diformyltricyclodecanes (DFTD) as the starting material could be used for the synthesis of various agricultural chemicals, lubricating oils, perfumes, plasticisers and pharmaceuticals [2–5]. DFTD could be further derivatised to produce high value-added chemicals such as tricyclodecanedimethylol (TDDMO) (see Scheme 1), which is an important intermediate and can be potentially used in the polymer and pharmaceutical industries, etc. [5,6]. TDDMO-derived polyester composites from the TDDMO esterification reaction have found widespread use in water-based dispersants, paints, lubricants, etc. [4,5,7,8]. Considering the major potential of DFTD in practical use, much research activity has been focused on the synthesis of DFTD. Currently, the synthesis of DFTD primarily utilises Rh- and Co-based catalysts and dicyclopentadiene (DCPD) as the starting material [9–16]. Ma et al. reported Co–Rh/ Fe3O4 modified with triphenylphosphine (PPh3) was also found to be an effective catalyst for 254

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OHC

OHC

CHO

DFTD

MFTD H2

OHC

DFTD

HOH2C CH2 OH

CHO

TDDMO

Scheme 1 MFTD conversion reaction pathway.

DCPD hydroformylation [9]. In another report, an 87.3% DFTD selectivity with > 99% DCPD conversion could be obtained using 2% Rh–2% Co/MCM-41 [10]. Chen and co-workers [11] reported that a 98 mol% aldehyde [MFTD (monoformyltricyclodecenes) and DFTD] yield could be obtained over a homogenous catalyst. As mentioned above, synthesis of DFTD primarily currently uses a one-step method in which DCPD as the starting material is directly converted to DFTD. In our latest work, however, the MFTD was produced in a few minutes (about 4 min) over Co–Rh/SiO2 catalysts and it was easy to obtain rather pure MFTD (> 99%) by controlling the reaction time [17]. Considering the advantages of much shorter reaction times with higher MFTD yield, we attempted to divide the overall hydroformylation of DCPD into two steps: step 1, the hydroformylation of DCPD to MFTD and step 2, the further hydroformylation of MFTD to DFTD. In the first step, adopting our latest reported method using Co–Rh/SiO2 catalysts in the reaction system, MFTD was obtained quickly and in high yield and then, in the second step, we sought an efficient catalytic process for the conversion of MFTD into DFTD. It appears that the second step is the rate-determining step of the overall hydroformylation of DCPD to DFTD. Recently, reports have appeared that nanopowders were used as catalyst supports [18–23]. However their application to hydroformylation has not been reported. Here, we explore for the first time the use of commercially available nanopowders as supports of the active Co–Rh bimetallic catalyst in hydroformylation. Hence, a series of supported ultra-low content Co–Rh bimetallic catalysts with various inorganic oxides, such as Al2O3, ZnO, TiO2 and CeO2 as the carrier, was used to catalyse the hydroformylation of MFTD to DFTD. The data suggested that the carrier played an important role in the catalytic performance in the MFTD hydroformylation. The 0.006 wt% Rh–0.006 wt% Co/ZnO catalyst showed the highest catalytic performance among the catalysts investigated and a 41.8% DFTD yield with 100% DFTD selectivity could be achieved. Furthermore, the kinetic profiles for MFTD hydroformylation over the 0.006 wt% Rh–0.030 wt% Co/ZnO catalyst have been examined systematically to explore the effect of reaction temperature on the catalytic performance in MFTD hydroformylation. These results collectively suggested that a particular reaction temperature promoted MFTD hydroformylation. There may be some agglomeration of the active sites at higher reaction temperatures. 2. EXPERIMENTAL 2.1 Materials All chemicals were of analytical grade and were used without further purification unless otherwise noted. www.prkm.co.uk

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2.2 Catalyst preparation The 0.006 wt% Rh–0.006 wt% Co/ZnO catalyst was prepared using commercially available nanopowder ZnO as a support and rhodium chloride and cobalt nitrate as the precursors. In brief, RhCl3·3H2O (1.228 mg) and Co(NO)2·6H2O (2.371 mg) were dissolved in distilled water (100 mL) and the solution was added dropwise into a Na2CO3 solution (600 mL, 0.47 M) containing ZnO (8 g) under vigorous stirring for 1.5 h. The reaction mixture was further stirred for 3 h. After filtration and washing to a pH of value 7.0 with distilled water (1000–1500 mL), the resultant precipitate was dried at 357 K for 16 h, then reduced under an H2 flow at 400 °C for 2 h. Finally, the 0.006 wt% Rh–0.006 wt% Co/ZnO catalyst (about 8 g) was obtained. The catalyst was denoted as 0.006% Rh–0.006% Co/ZnO. Other carrier-supported catalysts were prepared by the same method. 2.3 Reaction testing The hydroformylation of MFTD was performed in a 200 mL stainless steel autoclave reactor with an inserted glass liner. The reaction temperature was controlled by using an oil bath on a digital hotplate with a thermocouple. In a typical experiment, the catalyst (0.2 g), PPh3 ligand (0.3 g) and tetrahydrofuran (THF) (20 mL) were added and mixed in a high pressure reactor. Then the reactor was purged with syngas (the molar ratio of H2 to CO was 1:1) three times and finally pressurised to 4 MPa at room temperature. The reactor was heated to the desired reaction temperature with a stirring rate of 600 rpm, which was found to be adequate for overcoming diffusion limitations according to the initial rate test. An aliquot of liquid sample was withdrawn at specified times for further analysis. After the reaction, the catalyst could be separated from the reaction medium simply by filtration. In the case of the recyclability test of the catalyst, replenishment of the PPh3 ligand was needed because PPh3 was soluble in the solvent, which leached into the liquid after the reaction. 2.4 Reaction product analysis The reaction effluents were analysed by either gas chromatography (GC)–mass spectrometry (Agilent 6890/5973) or GC (Shimadzu 2014) instruments equipped with flame ionisation detectors. The definitions used in the results and discussion section include

MFTD conversion =

DFTD selectivity =

mol(MFTDin) − mol(MFTDout) × 100% mol(MFTDin)

mol(DFTD) × 100% mol(MFTDin) − mol(MFTDout)

(1)

(2)

where mol(MFTDin) is the introduced MFTD in moles, mol(MFTDout) is the unreacted MFTD in moles when the sample was taken for analysis and mol(DFTD) is the amount of DFTD in moles produced in the reaction. 3. RESULTS AND DISCUSSION 3.1 Effect of various carriers on the MFTD hydroformylation MFTD hydroformylation with different catalysts was carried out in a high pressure reactor under the conditions of 140 °C reaction temperature, 4 MPa reaction pressure, 180 min www.prkm.co.uk

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Table 1 Screening the catalysts for MFTD hydroformylationa Catalyst MFTD conversion (%) 0.006% Co/ZnO 22.40 0.006% Rh/ZnO 33.60 0.006% Rh–0.006% Co/TiO2 (rutile) 30.91 0.006% Rh–0.006% Co/TiO2 (anatase) 32.40 0.006% Rh–0.006% Co/CeO2 39.56 0.006% Rh–0.006% Co/Al2O3 29.40 0.006% Rh–0.006% Co/ZnO 41.80

DFTD yield (%) 22.40 33.26 30.91 32.40 39.56 29.10 41.80

DFTD selectivity (%) 100 99 100 100 100 99 100

a Experimental

conditions: 140 °C, 4 MPa reaction pressure, MFTD (1 g), catalyst (0.2 g), PPh3 (0.3 g), reaction time 180 min.

reaction time, MFTD (1 g), PPh3 (0.3 g), THF (20 mL) and catalyst (0.2 g) and the results are summarised in Table 1. As shown in Table 1, 100% DFTD selectivity could be obtained over all the catalysts. Only 22.4% and 33.26% DFTD yield could be obtained over 0.006% Co/ZnO and 0.006% Rh/ZnO catalysts respectively, while 41.8% DFTD yield could be achieved with 0.006% Rh–0.006% Co/ZnO as the catalyst. This suggested that (1) an enhanced DFTD yield could be achieved when the 0.006% Rh/ZnO catalyst was modified by cobalt, (2) the addition of cobalt could dramatically improve the DFTD yield under the same experimental conditions and (3) there should be a synergetic effect between Rh and Co in bimetallic catalysts. Clearly, the 0.006% Rh–0.006% Co/ZnO catalyst showed the highest catalytic performance among the catalysts used in this work and 41.8% DFTD yield was achieved, while only 29.1% DFTD yield was obtained over the 0.006% Rh–0.006% Co/Al2O3 catalyst. All these data suggested that different catalyst supports play an important role in the MFTD hydroformylation. The nanopowder ZnO support was chosen for further studies. 3.2 Effect of Co loading on DFTD yield The impacts of the different Co loadings on hydroformylation reactions were further investigated and the results are shown in Table 2. In catalytic reactions, different Co loadings in bimetallic catalysts usually affect the yield of the target product to a certain extent. So, the effect of Co loading on the MFTD hydroformylation was determined. The Rh/Co ratios were increased from 1:1 to 1:5 and the results are shown in Table 2. All the data points are normalised to the concentration of 1 g MFTD/20 mL THF. It can be seen that, compared with a Rh/Co ratio in the catalyst of 1:1, the DFTD yield was greatly increased from 30.91 to 53.46% when the Rh/Co ratio was 1:3 and when the Rh/Co ratio continued to be increased to 1:5 the DFTD yield slightly increased, suggesting that there is a synergetic effect between Co and Rh in the bimetallic catalysts and that an appropriate ratio of Rh/Co can improve the activity of the catalyst to achieve a higher DFTD yield.

Table 2 Effect of Co loading on DFTD yielda Catalyst 0.006% Rh–0.006% Co/ZnO 0.006% Rh–0.018% Co/ZnO 0.006% Rh–0.030 % Co/ZnO

MFTD conversion (%) 30.91 54.00 55.40

DFTD yield (%) 30.91 53.46 55.40

DFTD selectivity (%) 100 99 100

a Experimental conditions:140 °C, 4 MPa reaction pressure, MFTD (1 g), catalyst (0.2 g), PPh (0.3 g), 3 reaction time 90 min.

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80

120 130 140 150

Yield of DFTD (%)

70 60 50 40 30 20 10 0 0

20

40

60 80 100 120 140 Time (min)

Figure 1 Effect of reaction temperature on DFTD yield.

3.3 Effect of reaction temperature on DFTD yield The hydroformylation of MFTD was investigated at various reaction temperatures under the conditions of 4 MPa reaction pressure, 150 min reaction time, MFTD (1 g), PPh3 (0.3 g) and catalyst (0.2 g) and the results are shown in Figure 1. The catalyst used here was the 0.006 Rh–0.030 Co/ZnO catalyst. It can be seen that the yield of DFTD was increased on increasing the reaction time. The hydroformylation of MFTD to DFTD was divided into three stages. The order of the yield of DFTD at reaction time from 0 to 50 min was basically as follows: 140 °C > 150 °C > 130 °C > 120 °C, with 150 °C > 140 °C > 130 °C > 120 °C from 50 to 90 min and 140 °C > 130 °C > 150 °C > 120 °C from 90 to 150 min. At 150 min reaction time, the highest DFTD yield (80%) and DFTD formation rate was achieved at 140 °C, while the lowest DFTD yield (50.0%) and DFTD formation rate was observed at 120 °C. These data indicated that a particular reaction temperature might be needed to achieve a higher DFTD yield; a higher reaction temperature may not produce a higher DFTD yield, a possible reason being that the active sites become agglomerated at higher reaction temperatures. 3.4 Kinetic analysis To our knowledge, although many reports have mostly focused on the overall conversion and selectivity for DFTD, relatively few reports have dealt with the kinetic profiles for MFTD hydroformylation to understand the individual catalytic steps. Better kinetic information can provide insights into what is happening during the reaction process to optimise DFTD production. Here, the kinetics of MFTD hydroformylation over the 0.006 Rh–0.030 Co/ZnO catalyst were investigated. Initial MFTD conversion rates were used to construct ln([MFTD] t /[MFTD] 0) versus t plots [(Eqn (3)] to understand the intrinsic catalytic characteristics of the catalysts. Apparent energy analysis was also performed according to Eqn (4) [MFTD]𝑡𝑡 (3) ln = – 𝑘𝑘 𝑡𝑡 MFTD]0 www.prkm.co.uk

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Table 3 Effect of reaction temperature on kinetics and catalytic performance k (s–1) 7.21 × 10 –5 17.67 × 10 –5 16.74 × 10 –5 10.73 × 10 –5

Reaction temperature (°C) 120 130 140 150

-8.6 -8.8

In k

-9.0 -9.2 -9.4 -9.6 2.34 2.36 2.38 2.40 2.42 2.44 2.46 2.48 2.50 2.52 2.54 2.56

103*1/T (K-1) Figure 2 Arrhenius plot for hydroformylation of MFTD over 0.006 Rh–0.030 Co/ZnO catalyst.

Here [MFTD] t and [MFTD] 0 are the concentrations of MFTD at time t and initial MFTD concentration respectively, k is the rate coefficient of reaction and t is time in min.

𝐸𝐸 (4) + ln 𝐴𝐴 RT where k is the observed rate constant, E is the activation energy, T is the temperature in kelvin, R is the ideal gas constant and A is the pre-exponential factor. The correlation between reaction rate constant and temperature is plotted in Figure 2 and also shown in Table 3. When the reaction temperature rises from 120 to 140 °C the k value increases greatly first and then increases slightly; while sharp decrease was detected when the reaction temperature increased from 140 to 150 °C indicating that an appropriate reaction temperature accelerates the MFTD hydroformylation and excessive temperature may cause a decrease in catalyst activity because of agglomeration of active sites of the catalyst. ln 𝑘𝑘 = –

3.5 Catalyst recyclability study The recyclability of the 0.006 Rh–0.030 Co/ZnO catalyst was examined. The reactions were performed at 140 °C for 150 min. After reaction, the solution was cooled and the supernatant was decanted. The catalyst was washed extensively with THF and the same amount of THF, PPh3 and MFTD were added for the next run. As shown in Table 4, the catalyst could be reused at least three times without significant performance loss in DFTD production, revealing that the catalyst 0.006 Rh–0.030 Co/ZnO could be readily recycled in this reaction. www.prkm.co.uk

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Table 4 Reusability of 0.006 Rh–0.030 Co/ZnO catalyst Run 1st 2nd 3rd 4th

DFTD selectivity (%) 80.00 78.54 77.60 76.85

4. CONCLUSIONS The fabrication of 0.006 wt% Rh–0.006 wt% Co/ZnO (Al2O3, CeO2 and TiO2) catalysts involved the use of nanopowder ZnO (Al2O3, CeO2 and TiO2) as a support and rhodium chloride and cobalt nitrate as precursors. The prepared catalysts were tested for MFTD hydroformylation to DFTD. A 41.8% DFTD yield with 100% DFTD selectivity could be achieved over the 0.006% Co–0.006% Rh/ZnO catalyst, while only 29.1% DFTD yield was obtained under the same reaction conditions with the 0.006% Rh–0.006% Co/Al2O3 catalyst, suggesting that it is necessary to select an appropriate carrier for MFTD hydroformylation. The kinetics were studied systematically by examining the effect of reaction temperature. Kinetic analysis suggested that a particular reaction temperature might be needed to obtain a higher DFTD yield; a higher reaction temperature might instigate some agglomeration of the active sites. 5. ACKNOWLEDGEMENTS This work has been financially supported by the Chinese Government “Thousand Talent” Programme (Y42H291501), the Chinese Academy of Sciences (2015RC013) and the National Natural Science Foundation of China (U1139302, U1403192, 21506246). Published online: 10 October 2018 6. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]

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