Synthesis Of Methyl N-phenyl Carbamate Research Articles

Fabrication and characterization of ZrO2 and ZrO2/SiO2 catalysts and their application in the synthesis of methyl N-phenyl carbamate: a study of the reaction mechanism by using in situ FT-IR spectroscopy

Fabrication and characterization of ZrO2 and ZrO2/SiO2 catalysts and their application in the synthesis of methyl N-phenyl carbamate: a study of the reaction mechanism by using in situ FT-IR spectroscopy

Zn/Al/Pb Mixed Oxides as Efficient Heterogeneous Catalysts for the Synthesis of Methyl N-Phenyl Carbamate.

Dimethyl carbonate aminolysis is an effective and green pathway for the synthesis of methyl N-phenyl carbamate (MPC), which is an important intermediate for the synthesis of polyurethanes and many other chemicals. In this work, we demonstrate the fabrication of Zn/Al/Pb mixed oxides as efficient and stable heterogeneous catalysts for MPC synthesis. The catalysts are prepared via facile coprecipitation and subsequent thermal annealing. Their micromorphology and physical–chemical properties are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning TEM (STEM), X-ray photoelectron spectroscopy (XPS), and NH3-TPD. The results show that rather than being doped into ZnO and/or Al2O3, PbO is highly dispersed in the ZnO/Al2O3 base forming ultrafine nanoparticles. Despite the weak interactions within the mixed oxides, the high density of active sites generates outstanding catalytic activity and cycling stability for MPC synthesis, with an aniline conversion of almost 100% and MPC yield of up to 90% during six repeated tests, providing great potential for their further application.

One‐Pot Preparation of Methyl N‐Phenyl Carbamate and Zn(OAc)2/SiO2 Catalyst with Enhanced Stability

AbstractThe one‐pot preparation of methyl N‐phenyl carbamate (MPC) and supported Zn(OAc)2/SiO2‐OP was investigated. Zn(OAc)2 and SiO2 were added to the reaction between dimethyl carbonate (DMC) and aniline upon which MPC and Zn(OAc)2/SiO2‐OP were obtained simultaneously. The co‐prepared Zn(OAc)2/SiO2‐OP showed superior catalytic performance for MPC synthesis, giving a aniline conversion of 96.3% and a MPC selectivity of 99.7%. Compared with catalyst prepared by incipient impregnation, Zn(OAc)2/SiO2‐OP was more stable during the reaction, and the aniline conversion was 85.0% with MPC selectivity of 88.2% for the seventh time. The catalyst was characterized and the results suggested that Zn(OAc)2, Zn5(OH)8(OAc)2⋅2H2O, ZnO and Zn4O(OAc)6 are present on SiO2 surface. Zn(OAc)2 and Zn4O(OAc)6 are the active sites for MPC synthesis. The superior stability of the Zn(OAc)2/SiO2‐OP catalyst came from the presence of Zn4O(OAc)6.

Methyl N-phenyl carbamate synthesis over Zn/Al/Ce mixed oxide derived from hydrotalcite-like precursors.

Methyl N-phenyl carbamate (MPC) is an important intermediate for the green synthesis of methylene diphenyl diisocyanate (MDI) as well as many other important products. In the present work, Zn/Al/Ce mixed oxides derived from hydrotalcite-like precursors were employed as effective and recoverable heterogeneous catalyst for MPC synthesis via DMC aminolysis. Zn/Al/Ce hydrotalcite-like precursors prepared via coprecipitation method and the resulting catalysts were characterized by means of XRD, BET, SEM and XPS. Strong interactions within the Zn/Al/Ce mixed oxides were observed via the addition of appropriate amount of cerium. The mixed oxides containing 2.5% cerium showed high DMC aminolysis activity giving aniline conversion of 95.8%, MPC selectivity of 81.6% and MPC yield of 78.2%. Moreover, as a heterogeneous catalyst, it also exhibited superiorities of easy recovery and recyclable stability for MPC synthesis.

The Induction Period and Novel Active Species in Zn(OAc)2 Catalyzed Synthesis of Aromatic Carbamates

Zn(OAc)2 is known to exhibit excellent catalytic activity for aromatic carbamate synthesis by the reaction of aromatic amine and dimethyl carbonate (DMC). It is determined that an induction period exists during the synthesis of dimethyl-4,4′-methylenediphenyl dicarbamate (MDC) and methyl N-phenyl carbamate (MPC), although this period is more evident in the case of MDC. Zn(OAc)2 is able to catalyze the reaction of amine and DMC, but also react with DMC to form Zn4O(OAc)6, which also shows excellent catalytic activity for carbamate synthesis. As for MDC synthesis, Zn4O(OAc)6 plays the important role. However, Zn(OAc)2 plays the leading role in MPC synthesis. The deactivation of Zn4O(OAc)6 was also investigated. Zn4O(OAc)6 was initially transformed into Zn5(OH)8(OAc)2·2H2O (LHZA) and then into ZnO.

Cerium dioxide catalyzed synthesis of methyl N-phenylcarbamate from carbon dioxide, aniline and methanol in the presence of n-butyllithium

Direct synthesis of methyl N-phenylcarbamate (MPC) from carbon dioxide (CO2), aniline and methanol catalyzed by cerium dioxide (CeO2) in the presence of n-butyllithium (BuLi) was developed. The catalytic activity of CeO2 was significantly improved by the addition of BuLi. The conversion of aniline and the yield of MPC were dependent on the amount of CeO2 and BuLi, reaction conditions including the pressure of CO2, reaction time and temperature, and 9.4% yield of MPC was obtained under the optimized conditions. The formation pathway of MPC was also investigated in detail by varying reactants based on previously reported investigations, and phenyl isocyanate (PI) was believed to be the intermediate for the synthesis of MPC. A possible reaction pathway for the direct synthesis of MPC from CO2, aniline and methanol was proposed.

Influence of Solvent on Reaction Path to Synthesis of Methyl N-Phenyl Carbamate from Aniline, CO2 and Methanol

Methyl N-phenyl carbamate (MPC), an important organic chemical, can be synthesized from aniline, CO2 and methanol. Catalyst Cu-Fe/ZrO2-SiO2 was first prepared and its catalytic performance for MPC synthesis was evaluated. Then the influence of solvent on the reaction path of MPC synthesis was investigated. It is found that the reaction intermediate is different with acetonitrile or methanol as a solvent. With acetonitrile as a solvent, the synthesis of MPC follows the reaction path with diphenyl urea as the intermediate, while with methanol as a solvent the reaction occurs via the reaction path with dimethyl carbonate as the intermediate. The catalytic mechanism of cooperative catalysis comprising metal sites, Lewis acid sites and Lewis base sites is proposed according to different reaction intermediates.

Investigation of supported Zn(OAc)2 catalyst and its stability in N-phenyl carbamate synthesis

Zn(OAc)2 was found to give excellent catalytic performance for methyl N-phenyl carbamate (MPC) synthesis from aniline and dimethyl carbonate (DMC). However, after being used for only once it tended to lose activity because of the formation of ZnO by the reaction of Zn(OAc)2 and methanol. Zn(OAc)2/SiO2 was prepared by incipient impregnation and it gave excellent catalytic performance in MPC synthesis, on which aniline conversion and MPC yield were 98.1% and 93.8%, respectively. And Zn(OAc)2/SiO2 was found to be more stable than Zn(OAc)2 during the reaction. When Zn(OAc)2/SiO2 was used for the fifth time, aniline conversion and MPC yield were found to be 64.3% and 38.1%, respectively. The Zn(OAc)2/SiO2 catalyst was characterized by TG-DTA, ICP, FTIR, XRD and XPS. The characterization results suggested that the deactivation of Zn(OAc)2/SiO2 was also due to the formation of ZnO and there were two reasons for the improved stability of Zn(OAc)2/SiO2 catalyst. One was the formation of the Si–O–Zn bonds in Zn(OAc)2/SiO2 catalyst, which increased the steric hindrance of Zn and consequently retarded the reaction between Zn(OAc)2 and methanol. The other cause was the dehydration between methanol and the hydroxyl group on the SiO2 surface, which reduced the chance of a reaction between methanol and Zn(OAc)2.

Reaction Path of One-Pot Synthesis of Methyl N-Phenyl Carbamate from Aniline, Urea, and Methanol

One-pot synthesis of methyl N-phenyl carbamate (MPC) from aniline, urea, and methanol is a green reaction route. However, along which reaction path the reaction proceeds is still unclear and thereby the reaction mechanism cannot be determined. So the present work put much more emphasis on the analysis of the reaction path of MPC synthesis from aniline, urea, and methanol. First, the components in this reaction system were identified by means of gas-phase chromatograph (GC), high-performance liquid chromatograph (HPLC), and HPLC–mass spectrometry (MS) analyses. On the basis of the change tendency of the reaction components with reaction time, five plausible reaction paths were conjectured: one proceeds via a dimethyl carbonate intermediate, another utilizes methyl carbamate as an intermediate, still another passes a 1-phenyl biuret intermediate, yet another takes place through a phenylurea intermediate, and the last one carries on using diphenylurea as an intermediate. Then on the basis of thermodynamic analysis of the five possible reaction paths in combination with necessary experimental verifications, the one via a phenylurea intermediate was determined as the major reaction path in the absence of catalyst. Lastly, the influence of catalyst on the reaction path was studied and the result showed that the reaction path changed from through the phenylurea intermediate to the methyl carbamate intermediate in the presence of γ-Al2O3 catalyst.

Synthesis of Methyl N-Phenyl Carbamate Catalyzed by Ionic Liquid-Promoted Zinc Acetate

A series of ionic liquid-promoted zinc acetate catalysts (Zn(OAc)2-ILs) were prepared by separately mixing anhydrous zinc acetate with one of some ionic liquids, and their catalytic performance for the synthesis of methyl N-phenyl carbamate (MPC) from aniline and dimethyl carbonate (DMC) was evaluated. Among the catalysts, Zn(OAc)2-[bmim]PF6 showed the best catalytic performance. Under the suitable reaction conditions, aniline conversion and MPC selectivity were 99.8% and 99.1%, respectively. Moreover, Zn(OAc)2-[bmim]PF6 could be used five times without a significant loss in its catalytic performance. The mechanism for the promotion of ionic liquid [bmim]PF6 on the catalytic performance of zinc acetate was investigated by means of FT-IR analysis. The results show that a hydrogen bond is formed between the carbonyl oxygen of zinc acetate and the C2–H on an imidazoiume ring of [bmim]PF6. As a result, the zinc acetate changes from a bidentate to a unidentate coordination structure. Simultaneously, this chang...

Non-phosgene synthesis of isocyanates based on CO 2: Synthesis of methyl N-phenyl carbamate through coupling route with lead compound catalysts

The synthesis of methyl N-phenyl carbamate (MPC), the key intermediate for the non-phosgene synthesis of isocyanates based on CO 2, was studied from the reaction of dimethyl carbonate and N, N′-diphenyl urea under pressure. A variety of solid catalysts were screened, which showed lead compounds such as PbO, PbO 2, PbCO 3, and 2PbCO 3·Pb(OH) 2 had excellent catalytic activity. The characterization of XRD showed that the screened lead compound catalysts after reaction were changed into the same lead compound with the group –PbOH. With the increase of recycling times of the used lead compound catalysts, the selectivity of MPC and conversion of DPU were still about 99%. And the characterization of XRD and FTIR showed that new lead compound, which was produced with the increase of recycling times of the used lead compound catalysts, was also a lead compound with –PbOH. So the above results indicated that the real lead catalyst was the compound containing –PbOH. A possible reaction mechanism was discussed with the lead compound catalysts.

One Pot Synthesis of Methyl N-Phenyl Carbamate from Aniline, Urea and Methanol

Methyl N-phenyl carbamate (MPC) was synthesized from aniline, urea and methanol. The effects of catalysts, loading amounts, preparation condition of catalyst and reaction condition on the synthesis of MPC were investigated. It was shown that KNO3 modified zeolite HY gave the best performance to MPC formation among the evaluated catalysts, over which 93.1% aniline conversion and 82.6% MPC selectivity were obtained under the optimum reaction condition. Additionally, a possible catalytic mechanism to the formation of MPC in this reaction was proposed.

Clean synthesis of methyl N‐phenyl carbamate over ZnO‐TiO2 catalyst

AbstractBACKGROUND: Methyl N‐phenyl carbamate (MPC) is an intermediate for the preparation of methylene diphenyl diisocyanate (MDI), which is an important monomer for polyurethane synthesis. The synthesis of MPC by the reaction of aniline and dimethyl carbonate (DMC) is becoming more and more attractive. However, most of the catalysts used in MPC synthesis are homogeneous and not environment‐friendly. Therefore, it is important and necessary to develop a new kind of oxide catalyst, that is not only friendly to the environment, but also exhibits higher activity and longer service time.RESULTS: A new heterogeneous catalyst, ZnO‐TiO2, was prepared for MPC synthesis. ZnO‐TiO2 catalyst with a molar ratio Ti/Zn = 2 and calcined at 673 K exhibited good catalytic activity: aniline conversion was 96.9% and MPC yield 66.7%.CONCLUSION: ZnO‐TiO2 exhibits better catalytic activity than ZnO or TiO2 alone, which may result from the formation of ZnTiO3 and Zn2TiO4. Compared with ZnTiO3, Zn2TiO4 has better selectivity for MPC synthesis. Lewis acid sites with weaker acid strength favour MPC synthesis. The catalyst activity can be recovered almost completely by calcination. Copyright © 2008 Society of Chemical Industry

Synthesis of methyl N-phenyl carbamate from dimethyl carbonate and 1,3-diphenyl urea under mild conditions

Synthesis of methyl N-phenyl carbamate from dimethyl carbonate and 1,3-diphenyl urea was investigated under atmospheric pressure. The results showed that homogenous catalyst sodium methoxide had the excellent activity to efficiently catalyze the synthesis of methyl N-phenyl carbamate under atmospheric pressure.

A non-phosgene route for synthesis of methyl N-phenyl carbamate derived from CO2 under mild conditions

A non-phosgene route for the synthesis of methyl N-phenyl carbamate from dimethyl carbonate and N,N′-diphenyl urea was studied under the mild conditions of atmospheric pressure. A series of homogenous and heterogenous catalysts were screened, and the homogenous catalyst sodium methoxide exhibited excellent activity in the synthesis of methyl N-phenyl carbamate under atmospheric pressure. The parameters of molar ratio of reactants, catalyst concentration, reaction time, number of additions of catalyst, reaction temperature and solvents in the synthesis of methyl N-phenyl carbamate were also investigated. A possible reaction mechanism with catalyst sodium methoxide was proposed.

Synthesis of Methyl N-Phenyl Carbamate from Aniline and Dimethyl Carbonate over Supported Zirconia Catalyst

The novel supported zirconia catalysts for the synthesis of methyl N-phenyl carbamate (MPC) from aniline and dimethyl carbonate (DMC) are investigated. The unknown byproduct is determined as N,N-dimethylaniline (DMA) by GC−MS. The basic thermodynamics data of the main reaction and side reactions are calculated using Benson's bond addition method. The results show that the synthesis of N-methylaniline (NMA) and DMA are the main competitive reactions to MPC synthesis. It is found that the best support for supported zirconia catalyst is SiO2 and that the best loading amount is 1%. The optimal reaction conditions over ZrO2/SiO2 are as follows: reaction temperature, 443.15 K; reaction time, 7 h; n(DMC)/n(aniline) = 20; catalyst/aniline = 25 wt %; the conversion of aniline is 98.6%; and the yield of MPC is 79.8%. The results of characterization for the fresh catalyst and the deactivated catalyst show that the decrease of the specific surface area is the reason for deactivation.

A new non-phosgene route for synthesis of methyl N-phenyl carbamate from phenylurea and methanol

Methyl N-phenyl carbamate (MPC) was synthesized via a new non-phosgene route by reaction of phenylurea with methanol. The effects of catalysts, reaction temperature, reaction time and molar ratio of methanol to phenylurea were investigated. It was found that the catalyst played an important role in this reaction. Although MPC can be prepared in the absence of catalyst, 95.21% conversion of phenylurea and 84.75% selectivity of MPC were obtained in the presence of methanol-pretreated PbO catalyst under the reaction condition of 413 K for 4 h. In addition, XRD and IR were used to identify the structure of pretreated PbO catalyst. It was found that PbO was transformed into Pb(OCH 3) 2 after the pretreatment with methanol at 413 K. An addition–elimination reaction mechanism for the formation of MPC via the reaction between phenyl urea and methanol was proposed, based on the product distribution.

A novel non-phosgene approach to the synthesis of methyl N-phenyl carbamate by a reaction of methanol with phenylurea

A novel non-phosgene process for the synthesis of methyl N-phenyl carbamate (MPC) by a reaction of phenylurea with methanol was studied. The reaction between phenylurea and methanol was found to be a spontaneous reaction that took place in the absence of catalyst and gave MPC as the main product. Addition of a catalyst markedly influenced the reaction behavior. A basic catalyst greatly enhanced the yield of MPC, whereas an acidic catalyst pro- moted the formation of aniline and methyl carbamate. Moderate strength of basicity showed the best catalytic per- formance in the cases studied. The mechanism of reaction and catalyst functioning was discussed.

A phosgene-free process for the synthesis of methyl N-phenyl carbamate by the reaction of aniline with methyl carbamate

Abstract A phosgene-free route for the synthesis of methyl N-phenyl carbamate (MPC) by the reaction of aniline with methyl carbamate in the presence of methanol was studied. Effects of catalysts, reaction temperature, reaction time, and catalyst content, the molar ratio of reactants and the content of water on the reaction were investigated. The results demonstrated that an aniline conversion of 90.1% and MPC selectivity of 99.7% were achieved when the reaction was carried out at 433 K for 4 h using ZnCl2 as a catalyst. A possible reaction mechanism was proposed based on the product distribution.

Catalytic Activity of Mesoporous Silica for Synthesis of Methyl N-Phenyl Carbamate from Dimethyl Carbonate and Aniline

Mesoporous silica MCM-41, especially an Al-containing one, showed high catalytic activity for synthesis of methyl N-phenyl carbamate from dimethyl carbonate and aniline at 363-383 K. It was easily separated from the product solution, and the catalyst was able to be used repeatedly.