Carbamate synthesis by solid-base catalyzed reaction of disubstituted ureas and carbonates

This is the published version. Copyright © The Royal Society of Chemistry 2001A simple and efficient methodology to prepare carbamates has been demonstrated for the first time from symmetrical ureas and organic carbonates in the presence of solid base catalysts

6-(4-Methyl­phen­yl)-2,10-dioxo-3,9-dioxa-6-aza-1(1,1′)-ferrocenacyclo­deca­phane

In the title compound, [Fe(C23H23NO4)], the two cyclo­penta­dienyl (Cp) rings are nearly parallel, with a dihedral angle of 2.1 (1)°. The distance between the centroids of the Cp rings is 3.277 (8) Å. The relative orientation of the two Cp rings is characterized by a torsion angle of −64.3 (3)° defined by the two centroids and two substituted atoms

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

<p>Abstract</p> <p>Background</p> <p>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.</p> <p>Results</p> <p>The XRD characterization identified a berlinite structure associated with both the AlPO₄and ZnAlPO₄catalysts. 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 ZnAlPO₄structure possessed a higher binding energy than those in ZnO, and as a result, a greater electron-attracting ability. It was found that ZnAlPO₄catalyzed 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 ZnAlPO₄was also proposed.</p> <p>Conclusion</p> <p>As a heterogeneous catalyst ZnAlPO₄berlinite is highly active and selective for the methoxycarbonylation of HDA with DMC. We propose that dimethylhexane-1,6-dicarbamate is formed <it>via </it>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.</p

Highly Selective Phosgene-Free Carbamoylation of Aniline by Dimethyl Carbonate under Continuous-Flow Conditions

Over the last 20 years organic carbamates have found numerous applications in pesticides, fungicides, herbicides, dyes, pharmaceuticals, cosmetics, and as protecting groups and intermediates for polyurethane synthesis. Recently, in order to avoid phosgene-based synthesis of carbamates, many environmentally benign and alternative pathways have been investigated. However, few examples of carbamoylation of aniline in continuous-flow apparatus have been reported. In this work, we report a high-yielding, dimethyl carbonate (DMC)-mediated carbamoylation of aniline in a fixed-bed continuously fed reactor employing basic zinc carbonate as catalyst. Several variables of the system have been investigated (i.e. molar ratio of reagents , flow rate, and reaction temperature) to optimize the operating conditions of the system

Exploit Social Relations in Sentiment Analysis of Social Media Content for Disaster Management

The world has witnessed the prevailing usage of social media for communication during disasters. Being able to monitor and predict public opinions on social media during disasters allows us to design more efficient and effective communication mechanisms during critical times. However, this potential is yet to be materialized due to difficulties in sentiment analysis of social media content. We propose to augment the effectiveness of such analysis by incorporating social relations in sentiment classification models. The proposed study extends previous work substantially by looking at a larger set of social relations and focusing on different communication goals at each stage of disaster management. In addition, we look at sentiments at both individual and community levels. The study can help formulate a better understanding of how opinions are formed and propagated during disasters, thus allow stakeholders to strategize for better communication

Tandem synthesis of &#946;-amino alcohols from aniline, dialkyl carbonate, and ethylene glycol

An efficient tandem route for selective synthesis of &#946;-amino alcohols from anilines, dialkyl carbonate and ethylene glycol in the presence of recyclable Na-Y zeolite has been demonstrated. Transesterification of dialkyl carbonate by ethylene glycol produce ethylene carbonate which further reacts with aniline to give &#946;-amino alcohols in a single step. This reaction system was studied under high-pressure as well as pot reaction condition. Various process parametric effects were investigated for the reaction of aniline, dialkyl carbonate, and ethylene glycol. It was observed that a maximum 51% yield of mono-&#946;-amino alcohol, i.e., N-phenylethanolamine (NPEA). is obtained under pressure conditions. The yield of NPEA was improved drastically (&gt;91%) by carrying out the reaction under pot conditions using diethyl carbonate as transesterification agent. Finally activity and selectivity of solid catalyst was explained on the basis of nature of active sites and pore structure of the catalyst

Carbamate synthesis by solid-base catalyzed reaction of disubstituted ureas and carbonates

A simple and efficient methodology to prepare carbamates has been demonstrated for the first time from symmetrical ureas and organic carbonates in the presence of solid base catalysts

Carbamate synthesis via transfunctionalization of substituted ureas and carbonates

Synthesis of carbamates from substituted ureas and organic carbonates has been demonstrated using di-n-butyltin oxide (DBTO) as a catalyst. Reactivity pattern of ureas indicated that substituents on ureas have no significant effect on the carbamate yields. While, the carbonate reactivity pattern seems to be following the rule that is expected based on the leaving group ability of alkoxides and phenoxide to form carbamate observed in aminolysis of carbonates, it has been shown that basicity of reacting urea plays a vital role in the catalytic activity of this reaction. The effect of reaction parameters such as temperature, catalyst loading, solvent, concentration of reactants, etc. were investigated for synthesis of methyl methyl carbamate (MMC). The Arrhenius activation energy for the reaction between dimethyl urea (DMU) and dimethyl carbonate (DMC) was found to be 7.57 kcal/mol. A reaction mechanism has been postulated explaining the role of DBTO in the synthesis of carbamate from urea and carbonate

Synthesis of β-amino alcohols from aromatic amines and alkylene carbonates using Na-Y zeolite catalyst

A simple, efficient, and environmentally benign methodology for the synthesis of β-amino alcohols from aromatic amines and alkylene carbonates in the presence of the highly active and reusable solid base catalyst Na-Y zeolite is demonstrated