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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 reaction time on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; DMC/HDA, 8; temperature, 353 K. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲), selectivity for selectivity for dicarbamate, monocarbamate and N-methylated-carbamate, respectively.)
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Figure 5: Effect of reaction time on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; DMC/HDA, 8; temperature, 353 K. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲), selectivity for selectivity for dicarbamate, monocarbamate and N-methylated-carbamate, respectively.)

Mentions: Figure 5 outlines the effect of reaction time on HDA conversion, yield of dicarbamate and selectivities for both the main- and by-products. With increasing reaction time, the HDA conversion increased quickly within 8 h and only slightly over longer reaction times, reaching a value of nearly 100%. The yield of dicarbamate increased, followed by a decrease, with a maximum value of 87% being achieved at a reaction time of 8 h. For all the reaction timeframes tested, the selectivity for dicarbamate was much higher than those for monocarbamate and N-methylated-carbamate. On prolonging the reaction timeframe, the selectivity for dicarbamate decreased gradually. The selectivity for monocarbamate presented a minimum and that for N-methylated-carbamate a maximum at a reaction time of 8 h. Thus the decrease in the yield of dicarbamate at a longer reaction time may be explained by the partial decomposition of dicarbamate to monocarbamate. It appears that too long a reaction time did not promote greater formation of dicarbamate – but rather resulted in a reduced yield. The optimum reaction time is suggested as being 8 h.


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 reaction time on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; DMC/HDA, 8; temperature, 353 K. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲), selectivity for 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 5: Effect of reaction time on HDA conversion, yield of dicarbamate and selectivity for reaction products. Reaction conditions: HDA, 200 mmol; ZnAlPO4, 1.0 g; DMC/HDA, 8; temperature, 353 K. (Legend: (□) HDA conversion; (○) yield of dicarbamate; (■), (●) and (▲), selectivity for selectivity for dicarbamate, monocarbamate and N-methylated-carbamate, respectively.)
Mentions: Figure 5 outlines the effect of reaction time on HDA conversion, yield of dicarbamate and selectivities for both the main- and by-products. With increasing reaction time, the HDA conversion increased quickly within 8 h and only slightly over longer reaction times, reaching a value of nearly 100%. The yield of dicarbamate increased, followed by a decrease, with a maximum value of 87% being achieved at a reaction time of 8 h. For all the reaction timeframes tested, the selectivity for dicarbamate was much higher than those for monocarbamate and N-methylated-carbamate. On prolonging the reaction timeframe, the selectivity for dicarbamate decreased gradually. The selectivity for monocarbamate presented a minimum and that for N-methylated-carbamate a maximum at a reaction time of 8 h. Thus the decrease in the yield of dicarbamate at a longer reaction time may be explained by the partial decomposition of dicarbamate to monocarbamate. It appears that too long a reaction time did not promote greater formation of dicarbamate – but rather resulted in a reduced yield. The optimum reaction time is suggested as being 8 h.

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