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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.

No MeSH data available.


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Effect of the reaction temperature on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; DMC/HDA, 8; time, 8 h. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲), selectivity for dicarbamate, monocarbamate and N-methylated-carbamate, respectively.)
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Figure 4: Effect of the reaction temperature on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; DMC/HDA, 8; time, 8 h. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲), selectivity for dicarbamate, monocarbamate and N-methylated-carbamate, respectively.)

Mentions: Figure 4 presents the effect of reaction temperature on HDA conversion, yield of dicarbamate and selectivities for both the main- and by-products. On increasing reaction temperature, the conversion of HDA increased rapidly over the temperature range 333 to 349 K, and only slightly at temperatures higher than 349 K, approaching its maximum of 98%. The yield of dicarbamate increased with on moving from 333 to 349 K, attaining a maximum of 92.5% at 349 K, before decreasing at higher temperatures. The selectivity for dicarbamate first increased and then decreased, on increasing the reaction temperature. The maximum selectivity for dicarbamate was achieved at 349 K. The selectivity for monocarbamate presented an inverse trend with reaction temperature, compared with that for dicarbamate, and achieved a minimum value at 349 K. The selectivity for N-methylated-carbamate was almost unchanged with reaction temperature. It appears that the decrease in selectivity for dicarbamate at temperatures higher than 349 K was due to the increase in that for monocarbamate. For all the reaction temperature points tested, the selectivity for various products was: dicarbamate >> monocarbamate > N-methylated-carbamate. The above results indicate that the elevation of reaction temperature promoted the conversion of HDA. Although a higher conversion of HDA could be attained at high temperature, too high a temperature reduced the yield of dicarbamate – possibly due to the partial decomposition of dicarbamate into monocarbamate. Thus, the optimum reaction temperature for the production of dicarbamate from the methoxycarbonylation of HDA with DMC is around 349 K.


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 reaction temperature on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; DMC/HDA, 8; time, 8 h. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲), 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 4: Effect of the reaction temperature on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; DMC/HDA, 8; time, 8 h. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲), selectivity for dicarbamate, monocarbamate and N-methylated-carbamate, respectively.)
Mentions: Figure 4 presents the effect of reaction temperature on HDA conversion, yield of dicarbamate and selectivities for both the main- and by-products. On increasing reaction temperature, the conversion of HDA increased rapidly over the temperature range 333 to 349 K, and only slightly at temperatures higher than 349 K, approaching its maximum of 98%. The yield of dicarbamate increased with on moving from 333 to 349 K, attaining a maximum of 92.5% at 349 K, before decreasing at higher temperatures. The selectivity for dicarbamate first increased and then decreased, on increasing the reaction temperature. The maximum selectivity for dicarbamate was achieved at 349 K. The selectivity for monocarbamate presented an inverse trend with reaction temperature, compared with that for dicarbamate, and achieved a minimum value at 349 K. The selectivity for N-methylated-carbamate was almost unchanged with reaction temperature. It appears that the decrease in selectivity for dicarbamate at temperatures higher than 349 K was due to the increase in that for monocarbamate. For all the reaction temperature points tested, the selectivity for various products was: dicarbamate >> monocarbamate > N-methylated-carbamate. The above results indicate that the elevation of reaction temperature promoted the conversion of HDA. Although a higher conversion of HDA could be attained at high temperature, too high a temperature reduced the yield of dicarbamate – possibly due to the partial decomposition of dicarbamate into monocarbamate. Thus, the optimum reaction temperature for the production of dicarbamate from the methoxycarbonylation of HDA with DMC is around 349 K.

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