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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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A proposed mechanism for the methoxycarbonylation of 1,6-hexanediamine with DMC over ZnAlPO4.
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C1: A proposed mechanism for the methoxycarbonylation of 1,6-hexanediamine with DMC over ZnAlPO4.

Mentions: Although mechanistic studies on the methoxycarbonylation of HDA with DMC in the presence of a ZnAlPO4 catalyst are still in progress, it can be surmised that the reaction pathway may involve a catalytic cycle that involves a number of steps (Scheme 1). At first, DMC is activated because of its coordination to Zn(II), forming the species I as an active intermediate. Then, the carbonyl carbon in is attacked by the nucleophilic HDA, forming a reaction intermediate species IIa and methanol as a by-product. The interaction of the zinc ion in species IIa with another molecule of DMC results in the formation of monocarbamate and the recovery of the active intermediate species I. Similarly, the dicarbamate product may be result from the interaction between DMC and species IIb, which is formed by a nucleophilic attack of monocarbamate on the active intermediate species I. It must be noted that DMC, which has an ambident electrophilic nature, may react with a nucleophile not only at the carbonyl group to form carbamate, but also at the methyl moiety, forming the N-methylated product [35,36]. The carbonyl carbon, being a better electrophile, is expected to be more reactive with the amine than the methoxyl carbon For this reason, only a very limited amount of N-methylated product was formed during the reaction between HDA and DMC over the ZnAlPO4 catalyst.


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)

A proposed mechanism for the methoxycarbonylation of 1,6-hexanediamine with DMC over ZnAlPO4.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

C1: A proposed mechanism for the methoxycarbonylation of 1,6-hexanediamine with DMC over ZnAlPO4.
Mentions: Although mechanistic studies on the methoxycarbonylation of HDA with DMC in the presence of a ZnAlPO4 catalyst are still in progress, it can be surmised that the reaction pathway may involve a catalytic cycle that involves a number of steps (Scheme 1). At first, DMC is activated because of its coordination to Zn(II), forming the species I as an active intermediate. Then, the carbonyl carbon in is attacked by the nucleophilic HDA, forming a reaction intermediate species IIa and methanol as a by-product. The interaction of the zinc ion in species IIa with another molecule of DMC results in the formation of monocarbamate and the recovery of the active intermediate species I. Similarly, the dicarbamate product may be result from the interaction between DMC and species IIb, which is formed by a nucleophilic attack of monocarbamate on the active intermediate species I. It must be noted that DMC, which has an ambident electrophilic nature, may react with a nucleophile not only at the carbonyl group to form carbamate, but also at the methyl moiety, forming the N-methylated product [35,36]. The carbonyl carbon, being a better electrophile, is expected to be more reactive with the amine than the methoxyl carbon For this reason, only a very limited amount of N-methylated product was formed during the reaction between HDA and DMC over the ZnAlPO4 catalyst.

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