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Catalysis over zinc-incorporated berlinite (ZnAlPO4) of the methoxycarbonylation of 1,6-hexanediamine with dimethyl carbonate to form dimethylhexane-1,6-dicarbamate.

Sun DL, Deng JR, Chao ZS - Chem Cent J (2007)

Bottom Line: The FT-IR result confirmed the incorporation of zinc into the berlinite framework for ZnAlPO4.It was found that ZnAlPO4 catalyzed the formation of dimethylhexane-1,6-dicarbamate from the methoxycarbonylation of HDA with DMC, while no activity was detected on using AlPO4.Based on these results, a possible mechanism for the methoxycarbonylation over ZnAlPO4 was also proposed.

View Article: PubMed Central - HTML - PubMed

Affiliation: College of Chemistry and Chemical Engineering, Hunan University, Changsha, People's Republic of China. sdlei80@yahoo.com.cn

ABSTRACT

Background: The alkoxycarbonylation of diamines with dialkyl carbonates presents promising route for the synthesis of dicarbamates, one that is potentially 'greener' owing to the lack of a reliance on phosgene. While a few homogeneous catalysts have been reported, no heterogeneous catalyst could be found in the literature for use in the synthesis of dicarbamates from diamines and dialkyl carbonates. Because heterogeneous catalysts are more manageable than homogeneous catalysts as regards separation and recycling, in our study, we hydrothermally synthesized and used pure berlinite (AlPO4) and zinc-incorporated berlinite (ZnAlPO4) as heterogeneous catalysts in the production of dimethylhexane-1,6-dicarbamate from 1,6-hexanediamine (HDA) and dimethyl carbonate (DMC). The catalysts were characterized by means of XRD, FT-IR and XPS. Various influencing factors, such as the HDA/DMC molar ratio, reaction temperature, reaction time, and ZnAlPO4/HDA ratio, were investigated systematically.

Results: The XRD characterization identified a berlinite structure associated with both the AlPO4 and ZnAlPO4 catalysts. The FT-IR result confirmed the incorporation of zinc into the berlinite framework for ZnAlPO4. The XPS measurement revealed that the zinc ions in the ZnAlPO4 structure possessed a higher binding energy than those in ZnO, and as a result, a greater electron-attracting ability. It was found that ZnAlPO4 catalyzed the formation of dimethylhexane-1,6-dicarbamate from the methoxycarbonylation of HDA with DMC, while no activity was detected on using AlPO4. Under optimum reaction conditions (i.e. a DMC/HDA molar ratio of 8:1, reaction temperature of 349 K, reaction time of 8 h, and ZnAlPO4/HDA ratio of 5 (mg/mmol)), a yield of up to 92.5% of dimethylhexane-1,6-dicarbamate (with almost 100% conversion of HDA) was obtained. Based on these results, a possible mechanism for the methoxycarbonylation over ZnAlPO4 was also proposed.

Conclusion: As a heterogeneous catalyst ZnAlPO4 berlinite is highly active and selective for the methoxycarbonylation of HDA with DMC. We propose that dimethylhexane-1,6-dicarbamate is formed via a catalytic cycle, which involves activation of the DMC by a key active intermediate species, formed from the coordination of the carbonyl oxygen with Zn(II), as well as a reaction intermediate formed from the nucleophilic attack of the amino group on the carbonyl carbon.

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Effect of the DMC/HDA molar ratio on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; timeframe, 8 h; temperature, 353 K. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲) denote selectivity for dicarbamate, monocarbamate and N-methylated-carbamate, respectively.)
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Figure 3: Effect of the DMC/HDA molar ratio on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; timeframe, 8 h; temperature, 353 K. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲) denote selectivity for dicarbamate, monocarbamate and N-methylated-carbamate, respectively.)

Mentions: Figure 3 presents the effect of the DMC/HDA molar ratio on HDA conversion and yield of dicarbamate, in addition to selectivities for both the main- and by-products. On increasing the DMC/HDA molar ratio from 2:1 to 8:1, the conversion of HDA and the yield of dicarbamate increased rapidly. Subsequently the HDA conversion increased at a smaller rate and reached a value of as high as 99% when DMC/HDA = 10:1. The yield of dicarbamate increased, followed by a decrease, with the DMC/HDA increasing from 8:1 to 10:1. The maximum yield of dicarbamate was 87%, obtained at a DMC/HDA molar ratio of 8:1. The selectivities for dicarbamate, monocarbamate and N-methylated-carbamate were almost unchanged for HDA/DMC molar ratios over the range of 2:1 to 6:1, while that for dicarbamate decreased. Selectivities for monocarbamate and N-methylated-carbamate increased when DMC/HDA > 6:1. For all the HDA/DMC ratios tested, the selectivity for the main product (dicarbamate) was much larger than for the by-products (monocarbamate and N-methylated-carbamate). It appears that a higher DMC/HDA ratio was favorable for the conversion of HDA and the formation of dicarbamate, but too high a ratio led to a decrease in the yield of dicarbamate. Thus, the optimum DMC/HDA ratio appears to be in the range of 6:1 to 8:1.


Catalysis over zinc-incorporated berlinite (ZnAlPO4) of the methoxycarbonylation of 1,6-hexanediamine with dimethyl carbonate to form dimethylhexane-1,6-dicarbamate.

Sun DL, Deng JR, Chao ZS - Chem Cent J (2007)

Effect of the DMC/HDA molar ratio on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; timeframe, 8 h; temperature, 353 K. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲) denote selectivity for dicarbamate, monocarbamate and N-methylated-carbamate, respectively.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2211281&req=5

Figure 3: Effect of the DMC/HDA molar ratio on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; timeframe, 8 h; temperature, 353 K. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲) denote selectivity for dicarbamate, monocarbamate and N-methylated-carbamate, respectively.)
Mentions: Figure 3 presents the effect of the DMC/HDA molar ratio on HDA conversion and yield of dicarbamate, in addition to selectivities for both the main- and by-products. On increasing the DMC/HDA molar ratio from 2:1 to 8:1, the conversion of HDA and the yield of dicarbamate increased rapidly. Subsequently the HDA conversion increased at a smaller rate and reached a value of as high as 99% when DMC/HDA = 10:1. The yield of dicarbamate increased, followed by a decrease, with the DMC/HDA increasing from 8:1 to 10:1. The maximum yield of dicarbamate was 87%, obtained at a DMC/HDA molar ratio of 8:1. The selectivities for dicarbamate, monocarbamate and N-methylated-carbamate were almost unchanged for HDA/DMC molar ratios over the range of 2:1 to 6:1, while that for dicarbamate decreased. Selectivities for monocarbamate and N-methylated-carbamate increased when DMC/HDA > 6:1. For all the HDA/DMC ratios tested, the selectivity for the main product (dicarbamate) was much larger than for the by-products (monocarbamate and N-methylated-carbamate). It appears that a higher DMC/HDA ratio was favorable for the conversion of HDA and the formation of dicarbamate, but too high a ratio led to a decrease in the yield of dicarbamate. Thus, the optimum DMC/HDA ratio appears to be in the range of 6:1 to 8:1.

Bottom Line: The FT-IR result confirmed the incorporation of zinc into the berlinite framework for ZnAlPO4.It was found that ZnAlPO4 catalyzed the formation of dimethylhexane-1,6-dicarbamate from the methoxycarbonylation of HDA with DMC, while no activity was detected on using AlPO4.Based on these results, a possible mechanism for the methoxycarbonylation over ZnAlPO4 was also proposed.

View Article: PubMed Central - HTML - PubMed

Affiliation: College of Chemistry and Chemical Engineering, Hunan University, Changsha, People's Republic of China. sdlei80@yahoo.com.cn

ABSTRACT

Background: The alkoxycarbonylation of diamines with dialkyl carbonates presents promising route for the synthesis of dicarbamates, one that is potentially 'greener' owing to the lack of a reliance on phosgene. While a few homogeneous catalysts have been reported, no heterogeneous catalyst could be found in the literature for use in the synthesis of dicarbamates from diamines and dialkyl carbonates. Because heterogeneous catalysts are more manageable than homogeneous catalysts as regards separation and recycling, in our study, we hydrothermally synthesized and used pure berlinite (AlPO4) and zinc-incorporated berlinite (ZnAlPO4) as heterogeneous catalysts in the production of dimethylhexane-1,6-dicarbamate from 1,6-hexanediamine (HDA) and dimethyl carbonate (DMC). The catalysts were characterized by means of XRD, FT-IR and XPS. Various influencing factors, such as the HDA/DMC molar ratio, reaction temperature, reaction time, and ZnAlPO4/HDA ratio, were investigated systematically.

Results: The XRD characterization identified a berlinite structure associated with both the AlPO4 and ZnAlPO4 catalysts. The FT-IR result confirmed the incorporation of zinc into the berlinite framework for ZnAlPO4. The XPS measurement revealed that the zinc ions in the ZnAlPO4 structure possessed a higher binding energy than those in ZnO, and as a result, a greater electron-attracting ability. It was found that ZnAlPO4 catalyzed the formation of dimethylhexane-1,6-dicarbamate from the methoxycarbonylation of HDA with DMC, while no activity was detected on using AlPO4. Under optimum reaction conditions (i.e. a DMC/HDA molar ratio of 8:1, reaction temperature of 349 K, reaction time of 8 h, and ZnAlPO4/HDA ratio of 5 (mg/mmol)), a yield of up to 92.5% of dimethylhexane-1,6-dicarbamate (with almost 100% conversion of HDA) was obtained. Based on these results, a possible mechanism for the methoxycarbonylation over ZnAlPO4 was also proposed.

Conclusion: As a heterogeneous catalyst ZnAlPO4 berlinite is highly active and selective for the methoxycarbonylation of HDA with DMC. We propose that dimethylhexane-1,6-dicarbamate is formed via a catalytic cycle, which involves activation of the DMC by a key active intermediate species, formed from the coordination of the carbonyl oxygen with Zn(II), as well as a reaction intermediate formed from the nucleophilic attack of the amino group on the carbonyl carbon.

No MeSH data available.


Related in: MedlinePlus