ARTICLE pubs.acs.org/IECR
MgO-PbO Catalyzed Synthesis of Diethylene Glycol Bis(allyl carbonate) by Transesterification Route Hualiang An, Zhuo Gao, Xinqiang Zhao,* and Yanji Wang Hebei Provincial Key Lab of Green Chemical Technology and High Efficient Energy Saving, Hebei University of Technology, Tianjin 300130, China ABSTRACT: The catalytic performance of mixed metal oxides was evaluated for the synthesis of diethylene glycol bis(allyl carbonate) (ADC) by transesterification of diethylene glycol (DEG), dimethyl carbonate (DMC). and allyl alcohol (AAH), and MgOPbO was found to show the highest catalytic activity. The influence of preparation conditions on the catalytic performance of MgOPbO was studied and its suitable preparation conditions were as follows. A calcination process was used, with Mg(OH)2 and Pb(CH3COO)2 3 3H2O as precursors, molar ratio of Mg:Pb = 6:1, and calcination temperature of 650 °C. Under the following reaction conditions, molar ratio of DEG:DMC:AAH = 0.08:1:2, weight percentage of MgOPbO = 1.5% of total weight of all reactants, 100 °C, 6 h, and vacuum of 0.08 MPa, the yield of ADC was 97.3%. Moreover, MgOPbO showed a good recyclability; ADC yield of 95.4% could be achieved after the catalyst was reused for two times. The results of N2 adsorptiondesorption measurement and XPS analyses for MgOPbO indicate there exists an interaction between MgO and PbO, which promotes the catalytic performance and recyclability of MgOPbO. Furthermore, the reaction pathway for ADC synthesis was elucidated by means of GC-MS analysis and experimental verification.
1. INTRODUCTION Diethylene glycol bis(allyl carbonate) (abbreviated as ADC) is an important monomer for synthesizing polydiethylene glycol bis(allyl carbonate) which is commercially known as CR-39. CR39 has good physical and mechanical properties such as light weight, impact resistance, high light transmittance, good scuffresistance, and infrared and ultraviolet ray-resistance, so it is widely used as a substitute for glass in optics and vehicle windows. There are three routes to ADC synthesis: phosgenation route, CO2 route, and transesterification route. As the main industrial production process, phosgenation route using phosgene, diethylene glycol (DEG), and allyl alcohol (AAH) as raw materials possesses many advantages, e.g., high ADC yield, simple after-treatment process, mature production technology. This route, however, will be replaced gradually by nonphosgene routes for highly toxicity of phosgene, serious corrosion of byproduct hydrogen chloride and harmful effect of residual chlorine on ADC application. The CO2 route uses DEG, allyl chloride and greenhouse gas CO2 as reactants to prepare ADC and has better environmental merits.16 However, a large amount of base such as sodium carbonate is inevitably needed for neutralizing byproduct hydrogen chloride. In addition, residual chlorine also affects ADC purity. In contrast with CO2 route, the transesterification route (Scheme 1) using dimethyl carbonate (DMC) as the substitute of phosgene has obvious advantages such as no corrosion and high product purity because no hydrogen chloride is generated as a byproduct. Romano7 investigated ADC synthesis by transesterification route using basic catalysts such as sodium hydroxide, sodium carbonate, sodium alkoxide and anion exchange resin, and achieved a 90.2% yield of ADC at molar ratio of DEG:DMC:AAH = 2:25:50 and weight percentage of sodium methylate=0.1% of total weight of all reactants. The results revealed that the basic catalysts were r 2011 American Chemical Society
Scheme 1. Synthesis of ADC by Transesterification Route
effective for this transesterification reaction. However, these catalysts suffered from some problems such as difficulty in recovery and poor recyclability. Basic metal oxide catalysts have advantages of simple preparation procedure, high catalytic activity, easy separation and good thermal stability, so we have prepared a series of single metal oxide catalysts (e.g., Li2O, Na2O, K2O, MgO, CaO, ZnO, CuO, Fe2O3, La2O3, ZrO2) by a calcination process and evaluated their catalytic performance for ADC synthesis by transesterification route. The results showed that CaO had higher catalytic activity; ADC yield attained 79.7% under the conditions of molar ratio of DEG: DMC:AAH = 0.08:1:2, CaO weight percentage = 1.5% of total weight of all reactants, 100 °C, 6 h and vacuum of 0.08 MPa. However, CaO exhibited poor recyclability.8 In this paper, in order to enhance the activity and recyclability of metal oxide catalysts, several mixed metal oxides were prepared and their catalytic performance was evaluated in the Received: November 17, 2010 Accepted: May 11, 2011 Revised: April 4, 2011 Published: May 26, 2011 7740
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Industrial & Engineering Chemistry Research synthesis of ADC by transesterification route. Additionally, the reaction pathway for ADC synthesis was also elucidated by means of GC-MS and experimental verification.
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Table 1. Catalytic Performance of Mixed Metal Oxides for Synthesis of ADCa
2. EXPERIMENTAL SECTION
ADC yield ð%Þ ¼
moles of ADC formed 100% moles of DEG charged
The experiment process for determining the pathway is almost the same with that of activity test. The reaction products were quantitatively analyzed on a SP3420A gas chromatograph with a SE-30 capillary column. The analysis conditions were as follows: N2 as carrier, FID temperature of 290 °C, injection port temperature of 290 °C and the program-controlled column temperature: initial oven temperature of 70 °C for 3 min and then increasing with a rate of 10 °C min1 to 250 °C (held for 15 min). Diethyl phthalate was used as the internal standard to calculate ADC yield. The product mixture was identified qualitatively by Agilent 68905973GC-MSD GS-MS with a HP-5MS column. The analysis conditions were as follows: He as carrier, injection port
precursors
yield of ADC (%)
CaOPbO
Ca(NO3)2 3 4H2O þ Pb(NO3)2 Ca(NO3)2 3 4H2O þ Zn(NO3)2 3 6H2O Ca(NO3)2 3 4H2O þ Mg(NO3)2 3 6H2O
78.8 76.3 73.8
Mg(NO3)2 3 6H2O þ Ca(NO3)2 3 4H2O
76.0
CaOZnO CaOMgO
2.1. Preparation of Catalyst. All of the mixed-metal oxide
catalyst samples were prepared by calcinating their corresponding metal compounds. The preparation process was as follows: the metal compounds were mixed and ground first and then calcined at a certain temperature for a period of time. For example, for the preparation of MgOPbO with a Mg:Pb molar ratio of 4:1, Mg(OH)2 (11.7 g, 0.2 mol) and Pb(CH3 COO)2 3 3H2O (19.0 g, 0.05 mol) were mixed and then ground in a mortar by hand for about 3 min and finally calcined at 750 °C for 4 h in air. 2.2. Characterization of catalyst. X-ray diffraction (XRD) analysis was carried out using a D/MAX-2500 diffractometer with Cu KR radiation at 40 kV and 100 mA with a scanning range of 380°. Specific surface area and porosity of the samples were measured at 77 K by nitrogen adsorption using a Micromeritics ASAP 2020 surface area and porosity analyzer. X-ray photoelectron spectra (XPS) measurement was conducted on a PHI1600 ESCA SYSTEM. Mg KR radiation at 300 W and 15 kV was used as the light source and the vacuum system was controlled at about 1.33 106 Pa. The binding energy values of the XPS signals were calibrated by using adventitious C1s = 284.6 eV as a reference. FT-IR spectra of the samples were recorded on a Bruker Vector 22 FT-IR spectrophotometer in the range of 4000400 cm1 , with a resolution of 4 cm 1 and scanning rate of 0.2 cm s1 . Atomic absorption spectroscopy (AAS) was recorded on a Hitachi 18080 spectrometer. 2.3. Activity Test and Products Analysis. The reaction for synthesizing ADC from DEG, DMC, and AAH was carried out in a 250 mL three-necked flask fitted with a thermometer, a magnetic stirrer, and a distillation column connected to a vacuum for removing byproduct methanol released from the transesterification reaction. A typical reaction procedure was described below. After the three-necked flask was charged with 2.87 g of DEG, 30 mL of DMC, 46 mL of AAH, and 1.09 g of MgOPbO, the flask was heated to 100 °C and the reaction proceeded for 6 h at a vacuum of 0.08 MPa. The yield of ADC was calculated based on DEG
catalyst
MgOPbO MgOCaO MgOZnO a
Mg(NO3)2 3 6H2O þ Pb(NO3)2
Mg(NO3)2 3 6H2O þ Zn(NO3)2 3 6H2O
81.8 1.1
Reaction conditions: catalyst (molar ratio of Mg or Ca to another metal = 4:1) weight percentage = 1.5% of total weight of all reactants, molar ratio of DEG:DMC:AAH = 0.08:1:2, reaction time of 6 h, reaction temperature of 100 °C and reaction vacuum of 0.08 MPa.
Table 2. Effect of Precursors on Catalytic Performance of MgOPbOa precursors of magnesium
precursors of lead
(MgCO3)4 3 Mg(OH)2 3 5H2O Pb(NO3)2
Mg(NO3)2 3 6H2O
yield of ADC (%) 81.6
Pb(CH3COO)2 3 3H2O
83.8
PbCO3
83.5
Pb(NO3)2
81.8
Pb(CH3COO)2 3 3H2O
83.1
PbCO3
87.0
Mg(CH3COO)2 3 4H2O
Pb(NO3)2 Pb(CH3COO)2 3 3H2O
85.1 86.6
PbCO3
84.3
Mg(OH)2
Pb(NO3)2
80.2
Pb(CH3COO)2 3 3H2O
90.3
PbCO3
82.3
a
Reaction conditions: catalyst (Mg:Pb molar ratio=4:1) weight percentage=1.5% of total weight of all reactants, molar ratio of DEG:DMC: AAH=0.08:1:2, reaction time of 6 h, reaction temperature of 100 °C and reaction vacuum of 0.08 MPa.
temperature of 280 °C and the program-controlled column temperature: initial oven temperature of 70 °C for 3 min and then increasing with a rate of 10 °C min1 to 250 °C (held for 20 min). Mass spectra were collected with an ion source temperature of 230 °C and a scaning range of 10500 amu.
3. RESULTS AND DISCUSSION The catalytic performance of the prepared mixed metal oxide catalysts was evaluated and the reaction conditions described in our previous work8 were as follows: catalyst weight percentage = 1.5% of total weight of all reactants, molar ratio of DEG:DMC: AAH = 0.08:1:2, reaction time of 6 h, reaction temperature of 100 °C, and reaction vacuum of 0.08 MPa. 3.1. Screening of Catalyst. In our previous work,8 the catalytic behavior of alkali metal oxides, alkali-earth metal oxides and transition metal oxides had been evaluated under the following reaction conditions: molar ratio of DEG:DMC: AAH = 0.08:1:2, catalyst weight percentage = 1.5% of total weight of all reactants, 100 °C, 6 h, and vacuum of 0.08 MPa. The catalytic activity sequence was as follows: Li2O >Na2O > K2O > CaO > MgO > PbO > ZnO. Alkali metal oxides Li2O, Na2O, and K2O had high catalytic activity but poor stability in air, whereas alkali-earth metal oxides CaO and MgO were found to be the 7741
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Table 3. Specific Surface Area and Pore Volume of Samples sample
pore volume (cm3 g1) specific surface area (m2 g1)
MgO
0.3756
PbO
0.0007680
60.85
MgOPbOa
0.06704
16.37
MgOPbOMb
0.1579
25.91
0.6637
a
MgOPbO was prepared by a calcination process with Mg:Pb molar ratio of 4:1. b MgOPbOM was obtained by mixing MgO and PbO mechanically with Mg:Pb molar ratio of 4:1.
Figure 2. IR spectra of MgO, PbO, and MgOPbO; Mg:Pb molar ratio in MgOPbO sample is 4:1.
Figure 1. XRD patterns of the MgO, PbO, and MgOPbO samples: (() PbO, ()) MgO; Mg:Pb molar ratio in MgOPbO sample is 4:1.
suitable catalysts with ADC yield of 79.7 and 75.4%, respectively. The catalytic performance of CaO was evaluted further and the result showed that CaO had a poor recyclability: ADC yield decreased by 9.5% at the second run. To promote the catalytic activity and recyclability, CaO and MgO were separately matched with another metal oxide to form mixed metal oxides (molar ratio of Mg or Ca to another metal = 4:1). The mixed metal oxides were prepared using a calcination method at the calcination temperature of 750 °C and the calcination time of 4 h. Nitrate salts were selected as the precursors to eliminate the effect of anions on the catalytic performance. Table 1 shows the catalytic performance of the mixed metal oxides and MgOPbO was found to show the best catalytic performance. Hence the preparation of MgOPbO was studied further. 3.2. Effect of Preparation Conditions on Catalytic Performance of MgO-PbO. 3.2.1. Effect of Precursors. MgOPbO samples (Mg:Pb molar ratio of 4:1) were prepared by milling the corresponding precursors and subsequently calcinating at 750 °C for 4 h. The precursors and the catalytic performance of MgOPbO catalysts are listed in Table 2. MgOPbO prepared using Mg(OH)2 and Pb(CH3COO)2 3 3H2O as precursors shows the best performance and ADC yield is 90.3%. Because ADC yield was only 79.7% over CaO and 75.4% over MgO catalyst,8 MgOPbO exhibits much better catalytic performance than CaO or MgO. To study the effect of physical structure on the catalytic performance of the MgOPbO sample, we separately measured specific surface area and pore volume of MgO, PbO, and
Figure 3. Pore size distribution of PbO, MgO, and PbOMgO samples Mg:Pb molar ratio in MgOPbO sample is 4:1.
MgOPbO, and the results are listed in Table 3. The sample mixed mechanically by MgO and PbO with a Mg:Pb molar ratio of 4:1 is denoted as MgOPbOM, and its specific surface area and pore volume calculated using the corresponding values of MgO and PbO are 25.91 m2 g1 and 0.1579 cm3 g1, higher than that of MgOPbO sample. We think the differences in the specific surface area and pore volume between MgOPbO and MgOPbOM may be caused by the interaction of MgO with PbO. The XRD patterns and infrared spectra of MgO, PbO, and MgOPbO were separately presented in Figures 1 and 2. In Figure 2, the band centered at 2360 cm1 corresponds to PbO, the bands at 1457 and 3422 cm1 correspond to H2O adsorbed on the sample, and the band at 1641 cm1 corresponds to CO2 adsorbed on the sample. The band corresponding to MgO centers at 410 cm1 in pure MgO sample, whereas it appears at 512 cm1 in the MgOPbO sample. It might also be caused by the interaction of MgO with PbO. Although both Figures 1 and 2 show that there are no components appearing in the MgOPbO sample except MgO and PbO, we do not think the 7742
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Table 4. Binding Energy of Mg2p and Pb4f binding energy (eV) sample MgO
Mg2p 46.16
PbO MgOPbOa a
Pb4f
133.4 45.20
134.3
Mg:Pb molar ratio of 4:1.
Figure 4. Effect of Mg:Pb molar ratio on catalytic performance of MgO-PbO Reaction conditions: catalyst weight percentage = 1.5% of total weight of all reactants, molar ratio of DEG:DMC:AAH = 0.08:1:2, reaction time of 6 h, reaction temperature of 100 °C, and reaction vacuum of 0.08 MPa.
Figure 5. Effect of calcination temperature on catalytic performance of MgOPbO Reaction conditions: catalyst (Mg:Pb molar ratio of 6:1) weight percentage = 1.5% of total weight of all reactants, molar ratio of DEG:DMC:AAH = 0.08:1:2, reaction time of 6 h, reaction temperature of 100 °C, and reaction vacuum of 0.08 MPa.
MgOPbO sample is simply a physical mixture of MgO and PbO. To further illustrate that the MgOPbO sample is not a
physical mixture of MgO and PbO, we obtained the pore size distributions of the samples by N2 adsorptiondesorption measurments. As shown in Figure 3, there are hardly any pores in PbO sample and two pore size distribution peaks separately centered at 6.24 and 12.4 nm in MgO sample. In the MgOPbO sample, however, the peaks centered at 6.24 and 12.4 nm disappear and four new pore size distribution peaks appear at 2.11, 2.82, 4.78, and 7.63 nm. The results suggest that a new physical structure is generated in the MgOPbO sample, which may be caused by melt blending of Mg(OH)2 and Pb(CH3COO)2 3 3H2O in the preparation process. To further study whether there is an interaction between MgO and PbO in the MgOPbO sample or not, we performed XPS analyses of the samples; the results are given in Table 4. For MgOPbO sample, the Mg2p level is shifted to a lower binding energy by 0.96 eV, whereas the Pb4f level is shifted to a higher binding energy by þ0.90 eV. The change in the chemical environment for Mg and Pb indicates that there is an interaction between MgO and PbO. 3.2.2. Effect of Mg:Pb Molar Ratio and Calcination Temperature. The effect of Mg:Pb molar ratio and calcination temperature on the catalytic performance of MgOPbO is shown in Figures 4 and 5, respectively. The highest ADC yield is 97.3% over MgOPbO prepared with the suitable Mg:Pb molar ratio of 6:1 and suitable calcination temperature of 650 °C. The specific surface area and pore volume of the MgOPbO samples calcined at different temperatures were measured and the results are listed in Table 5. It can be seen that the specific surface area decreases with increasing calcination temperature as a result of sintering, whereas the pore volume increases first and then decreases. The maximum pore volume was observed at the calcination temperature of 650 °C and the highest ADC yield was obtained over the MgOPbO sample with the maximum pore volume. 3.3. Recyclability of MgOPbO Catalyst. To study the recyclability of MgOPbO catalyst, we recovered the used MgOPbO catalyst by filtrating, washing with 50 mL of dichloromethane, and then drying at 60 °C for 8 h under a vacuum of 0.08 MPa. The activity evaluation results of the recovered catalysts are illustrated in Figure 6. The yield of ADC is 97.3% at the first run and then decreases by only 1.9% at the second run and then keeps almost unchanged at the third run. The catalytic activity of the recovered catalysts decreases more rapidly in the succeeding two runs and ADC yield drops to 87.4% at the fifth run. Because the yield of ADC decreases by 9.5% at the second run over CaO,8 MgOPbO shows much better recyclability than CaO. Figure 7 shows the XRD patterns of the fresh, the first recovered and the fourth recovered MgOPbO catalysts. It is demonstrated that the diffraction peak of PbO almost disappeared, whereas the diffraction peaks of MgO scarcely changed in the recovered catalysts. The content (wt %) of Mg and Pb in the fresh and the fourth recovered catalysts was measured by atomic absorption spectrometry (AAS). The result is as follows: Mg 29.5, 29.4; Pb 39.6, 38.1. Pb content drops slightly and Mg content is almost unchanged. The slight loss of PbO may lead to the decrease of catalytic performance of the recovered catalyst. IR was employed to investigate the fresh and the fourth recovered catalysts. The characteristic peaks of PbO and MgO are observed in the infrared spectra (the band centered at 512 cm1 corresponds to MgO, the band at 2360 cm1 corresponds to PbO, the bands at 1457and 3422 cm1 correspond to H2O adsorbed on the MgOPbO sample, and the band at 7743
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Table 5. Specific Surface Area and Pore Volume of MgOPbOa Calcinated at Different Temperatures
a
calcination
pore volume
specific surface
temperature (°C)
(cm3 g1)
area (m2 g1)
550 650
0.05939 0.06704
17.92 16.45
750
0.03329
7.025
850
0.01139
3.638
Mg:Pb molar ratio of 6:1.
Figure 7. XRD patterns of the fresh and recovered catalysts: (() PbO, ()) MgO; Mg:Pb molar ratio in MgOPbO sample is 6:1.
Scheme 2. Possible Reaction Pathway for ADC Synthesis
Figure 6. Reuse of MgOPbO. Reaction conditions: catalyst (Mg:Pb molar ratio of 6:1) weight percentage = 1.5% of total weight of all reactants, molar ratio of DEG:DMC:AAH =0.08:1:2, reaction time of 6 h, reaction temperature of 100 °C, and reaction vacuum of 0.08 MPa.
1641 cm1 corresponds to CO2 adsorbed on the MgOPbO sample) of the fresh and the fourth recovered catalysts. The results of AAS and IR indicate the existence of PbO while PbO is not detected by XRD, suggesting that PbO may be in an amorphous or microcrystalline state in the recovered catalysts. 3.4. Possible Reaction Pathways for ADC Synthesis by Transesterification Route. 3.4.1. Qualitative Analysis of Reaction System. According to the GC-MS analysis results, besides DEG, DMC and AAH, the major components in the reaction system are methyl allyl carbonate (MAC), dially carbonate (DAC), diethylene glycol mono (allyl carbonate) (DGAC), ADC, diethylene glycol mono (methyl carbonate) (DGMC), and diethylene glycol dimethyl carbonate (DGDMC). 3.4.2. Experimental Verification of the Reaction Pathways. From the result of GC-MS analysis, two possible reaction pathways for ADC synthesis by transesterification route are proposed: (1) DAC is synthesized from DMC and AAH, and then reacts with DEG to ADC; (2) DGDMC is synthesized from DEG and DMC, and then reacts with AAH to ADC. We designed some verification experiments to determine which reaction pathway is correct. (1) Reaction Pathway 1. Designed experiment no. 1 and no. 2: to synthesize DAC from DMC and AAH, and then test whether the reaction needs a catalyst or not (reaction conditions: molar ratio of DMC:AAH = 1:3, 4 h, 100 °C, and weight percentage of
catalyst = 1.5% of total weight of all reactants in experiment no. 1, whereas no catalyst is used in experiment no. 2). The results show that there is a lot of DAC in the experiment no.1, whereas no DAC is found in experiment no. 2, indicating that the reaction for DAC synthesis can not take place without catalyst. Because a little MAC was also found in the reaction solution in experiment no. 1, we think that the reaction for DAC synthesis may proceed in two steps: MAC is formed from DMC and AAH at the first step, and then DAC is produced from the successive reaction of MAC and AAH. Designed experiment no. 3 and no. 4: to synthesize ADC from DAC and DEG, and then test whether the reaction needs a catalyst or not (reaction conditions: 4 h, 100 °C, vacuum of 0.07 MPa, and weight percentage of catalyst = 1.5% of total weight of all reactants in the experiment no. 3 while no catalyst in the experiment no. 4). The GC analysis results show that there 7744
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MgO and PbO. The interaction promotes the catalytic performance and recyclability of MgOPbO. (2) Under the following conditions: reaction temperature of 100 °C, reaction time of 6 h, molar ratio of DEG:DMC: AAH = 0.08:1:2, weight percentage of MgOPbO = 1.5% of total weight of all reactants and reaction vacuum of 0.08 MPa, the maximum yield of ADC is 97.3%. In addition, MgOPbO shows better recyclability than that of CaO. The results of AAS and IR analyses indicate that there exists PbO in recovered catalysts, whereas PbO can not be detected by XRD, suggesting that PbO may be in an amorphous or microcrystalline state in the recovered catalysts. (3) The reaction pathway for ADC synthesis by transesterification route is established on the basis of both GC-MS analysis and experimental verification. The results show that the reaction proceeds in four steps: (1) the formation of MAC from AAH and DMC; (2) the reaction of MAC with AAH to DAC; (3) the reaction of DAC with DEG to DGAC; (4) the formation of ADC from DGAC and DAC. In addition, two important side reactions are identified.
Scheme 3. Side Reactions for ADC Synthesis
are a lot of ADC and some DGAC in the experiment no. 3, whereas neither ADC nor DGAC are detected in the experiment no. 4, which indicates that the reaction can not take place without catalyst. With increasing vacuum, the content of ADC increased, whereas that of DGAC decreased. From these results, we speculate that the reaction for ADC synthesis from DAC and DEG may proceed in two steps: DGAC is first synthesized from DAC and DEG, and then DGAC reacts further with DAC to ADC. On the basis of the above experimental results, the reaction for the synthesis of ADC by transesterification route can proceed in four steps as shown in Scheme 2. (2) Reaction Pathway 2. Designed experiment no. 5 and no. 6: to synthesize DGDMC from DMC and DEG, and then test whether the reaction needs a catalyst or not (reaction conditions: malor ratio of DEG to DMC = 1:6, 4 h, 100 °C, and weight percentage of catalysts = 1.5% of total weight of all reactants in experiment no. 5, whereas no catalyst is used in experiment no. 6). The GC analysis results show that there are DGMC and DGDMC in experiment no. 5, whereas neither DGMC nor DGDMC is detected in experiment no. 6, indicating that the reaction for DGDMC synthesis could not happen without catalyst. The reaction may proceed in two steps: DMC reacts with DEG to form DGMC first, and then DGDMC is obtained by the reaction of DGMC and DMC. Designed experiment no. 7 and no. 8: to synthesize ADC from DGDMC and AAH, and then test whether the reaction needs a catalyst or not (reaction conditions: 4 h, 100 °C, vacuum of 0.07 MPa, and weight percentage of catalyst = 1.5% of total weight of all reactants in the experiment no. 7, whereas no catalyst is used in experiment no. 8). The GC analysis results show that there is no ADC either in experiment no.7 or in experiment no. 8, which indicates that reaction pathway (2) is infeasible. The reactions for the formation of DGMC and DGDMC are the side reactions for ADC synthesis as shown in Scheme 3. According to the results given above, the reaction pathway of ADC synthesis established by the experimental verification coincides well with that obtained by theoretical deduction in our previous work.8
4. CONCLUSION (1) Suitable preparation conditions for MgOPbO catalyst are as follows: using a calcination process, Mg(OH)2 and Pb(CH3COO)2 3 3H2O as precursors, molar ratio of Mg: Pb = 6:1, and calcination temperature of 650 °C. The N2 adsorptiondesorption measurement and XPS analysis results indicate that there exists an interaction between
’ AUTHOR INFORMATION Corresponding Author
*Fax: þ86-22-60204294. Tel: þ86-22-60202427. E-mail: zhaoxq@ hebut.edu.cn.
’ ACKNOWLEDGMENT This work was financially supported by Special Program of National Basic Research Program of China (973 Program) (Grant 2010CB234602), National Natural Science Foundation of China (Grant 20976035, 21076059), Science and Technological Research and Development Project of Hebei Province (Grant 072421107D), and Natural Science Foundation of Hebei province (Grant B2010000019). The authors are gratefully appreciative of their contributions. ’ REFERENCES (1) Shigemune, T.; Shibuya, M. Preparation of organic carbonate. JP 8102937, 1981. (2) Shigemune, T.; Shibuya, M. Preparation of organic carbonate. JP 8105442, 1981. (3) Shigemune, T.; Shibuya, M. Preparation of organic carbonate. JP 8105443, 1981. (4) William, M.; Dennis, R. Replacement of phosgene with carbon dioxide: Synthesis of alkyl carbonates. J. Org. Chem. 1995, 60, 6205. (5) An, H.; Zhao, X.; Liu, Z.; Jia, C.; Wang, Y. Synthesis of N,N,N0 , 0 N -tetramethyl-N00 -phenylguanidine and its catalytic performance for ADC synthesis via carbon dioxide route. J. Chem. Ind. Eng. 2008, 59, 590. (6) Sun, X.; Zhao, X.; An, H.; Wang, Y. Preparation of N-cyclohexylN0 ,N0 ,N00 ,N00 -tetramethylguanidine and its application in synthesis of diethylene glycol diallyl dicarbonate. Petrochem. Technol. 2008, 37, 602. (7) Romano, U. Process for synthesizing carbonic acid esters derived from unsaturated alcohols and polyhydric alcohols. US 4512930, 1985. (8) Gao, Z.; Zhao, X.; An, H.; Wang, Y. Synthesis of diethyene glycol bis(allyl carbonate) by transesterification route over CaO catalyst. Acta Petrol. Sin. 2010, 26, 684.
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