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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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The FT-IR spectrum of (a) AlPO4 and (b) ZnAlPO4.
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Figure 2: The FT-IR spectrum of (a) AlPO4 and (b) ZnAlPO4.

Mentions: Figure 2 shows the FT-IR spectra of the AlPO4 and ZnAlPO4 catalysts. The spectrum of the AlPO4 (Figure 2a) exhibited the characteristic vibration absorptions of a berlinite structure [19,26-29], i.e. the bands associated with vibrations of the [PO4]3- unit (1127, 1096, 530, 504, 468, 418, and 378 cm-1), those of the pseudolattice Al vibrations (705, 687, 670, 652, and 566 cm-1), and a band (748 cm-1) ascribed to an overtone of that at 378 cm-1 (or, a result of sub-lattice aluminium defects in berlinite). The spectrum of ZnAlPO4 (Figure 2b) also presented the above bands, some of which were shifted towards lower wavenumbers probably due to the incorporation of Zn into the berlinite framework. In addition, two additional bands at 1009 and 990 cm-1 were also detected in the ZnAlPO4spectrum compared to that for AlPO4. Thus, the bands at 1009 and 990 cm-1 should be caused by the incorporation of Zn into the berlinite framework and assigned to the vibrations of Zn-O-P [27,28]. Infrared bands characteristic of ZnO are only observed below 600 cm-1 and a broad band at 400–550 cm-1had been reported by Oliver [28]. For ZnAlPO4, the sharp bands – rather than broad bands – attributed to [PO4]3- vibrations were observed in the range of 300–550 cm-1, providing further evidence for the incorporation of Zn into the berlinite framework.


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)

The FT-IR spectrum of (a) AlPO4 and (b) ZnAlPO4.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: The FT-IR spectrum of (a) AlPO4 and (b) ZnAlPO4.
Mentions: Figure 2 shows the FT-IR spectra of the AlPO4 and ZnAlPO4 catalysts. The spectrum of the AlPO4 (Figure 2a) exhibited the characteristic vibration absorptions of a berlinite structure [19,26-29], i.e. the bands associated with vibrations of the [PO4]3- unit (1127, 1096, 530, 504, 468, 418, and 378 cm-1), those of the pseudolattice Al vibrations (705, 687, 670, 652, and 566 cm-1), and a band (748 cm-1) ascribed to an overtone of that at 378 cm-1 (or, a result of sub-lattice aluminium defects in berlinite). The spectrum of ZnAlPO4 (Figure 2b) also presented the above bands, some of which were shifted towards lower wavenumbers probably due to the incorporation of Zn into the berlinite framework. In addition, two additional bands at 1009 and 990 cm-1 were also detected in the ZnAlPO4spectrum compared to that for AlPO4. Thus, the bands at 1009 and 990 cm-1 should be caused by the incorporation of Zn into the berlinite framework and assigned to the vibrations of Zn-O-P [27,28]. Infrared bands characteristic of ZnO are only observed below 600 cm-1 and a broad band at 400–550 cm-1had been reported by Oliver [28]. For ZnAlPO4, the sharp bands – rather than broad bands – attributed to [PO4]3- vibrations were observed in the range of 300–550 cm-1, providing further evidence for the incorporation of Zn into the berlinite framework.

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