The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Yanmei Chen - One of the best experts on this subject based on the ideXlab platform.
-
consecutive lossen rearrangement transamidation reaction of hydroxamic acids under catalyst and additive free conditions
Organic and Biomolecular Chemistry, 2018Co-Authors: Heng Zhang, Dimei Chen, Yanmei ChenAbstract:The Lossen rearrangement is a classic process for transforming activated hydroxamic acids into isocyanate under basic or thermal conditions. In the current report we disclosed a consecutive Lossen rearrangement/transamidation reaction in which unactivated hydroxamic acids were converted into N-substituted Formamides in a one-pot manner under catalyst- and additive-free conditions. One feature of this novel transformation is that the formamide plays triple roles in the reaction by acting as a readily available solvent, a promoter for additive-free Lossen rearrangement, and a source of the formyl group in the final products. Acyl groups other than formyl could also be introduced into the product when changing the solvent to other low molecular weight aliphatic amide derivatives. The solvent-promoted Lossen rearrangement was better understood by DFT calculations, and the intermediacy of isocyanate and amine was supported well by experiments, in which the desired products were obtained in excellent yields under similar conditions. Not only monosubstituted Formamides were synthesized from hydroxamic acids, but also N,N-disubstituted Formamides were obtained when secondary amines were used as precursors.
-
Consecutive Lossen rearrangement/transamidation reaction of hydroxamic acids under catalyst- and additive-free conditions
Organic and Biomolecular Chemistry, 2018Co-Authors: Mengmeng Jia, Dimei Chen, Yanmei Chen, Heng Zhang, Yongjia Lin, Yuanzhi XiaAbstract:The Lossen rearrangement is a classic process for transforming activated hydroxamic acids into isocyanate under basic or thermal conditions. In the current report we disclosed a consecutive Lossen rearrangement/transamidation reaction in which unactivated hydroxamic acids were converted into N-substituted Formamides in a one-pot manner under catalyst- and additive-free conditions. One feature of this novel transformation is that the formamide plays triple roles in the reaction by acting as a readily available solvent, a promoter for additive-free Lossen rearrangement, and a source of the formyl group in the final products. Acyl groups other than formyl could also be introduced into the product when changing the solvent to other low molecular weight aliphatic amide derivatives. The solvent-promoted Lossen rearrangement was better understood by DFT calculations, and the intermediacy of isocyanate and amine was supported well by experiments, in which the desired products were obtained in excellent yields under similar conditions. Not only monosubstituted Formamides were synthesized from hydroxamic acids, but also N,N-disubstituted Formamides were obtained when secondary amines were used as precursors.
Julius Rebek - One of the best experts on this subject based on the ideXlab platform.
-
Relative hydrophilicities of cis and trans Formamides.
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Luis Escobar, Yu-jie Zhu, Yoram Cohen, Pablo Ballester, Julius RebekAbstract:Secondary Formamides are widely encountered in biology and exist as mixtures of both cis and trans isomers. Here, we assess hydrophilicity differences between isomeric Formamides through direct competition experiments. Formamides bearing long aliphatic chains were sequestered in a water-soluble molecular container having a hydrophobic cavity with an end open to the aqueous medium. NMR spectroscopic experiments reveal a modest preference (
Heng Zhang - One of the best experts on this subject based on the ideXlab platform.
-
consecutive lossen rearrangement transamidation reaction of hydroxamic acids under catalyst and additive free conditions
Organic and Biomolecular Chemistry, 2018Co-Authors: Heng Zhang, Dimei Chen, Yanmei ChenAbstract:The Lossen rearrangement is a classic process for transforming activated hydroxamic acids into isocyanate under basic or thermal conditions. In the current report we disclosed a consecutive Lossen rearrangement/transamidation reaction in which unactivated hydroxamic acids were converted into N-substituted Formamides in a one-pot manner under catalyst- and additive-free conditions. One feature of this novel transformation is that the formamide plays triple roles in the reaction by acting as a readily available solvent, a promoter for additive-free Lossen rearrangement, and a source of the formyl group in the final products. Acyl groups other than formyl could also be introduced into the product when changing the solvent to other low molecular weight aliphatic amide derivatives. The solvent-promoted Lossen rearrangement was better understood by DFT calculations, and the intermediacy of isocyanate and amine was supported well by experiments, in which the desired products were obtained in excellent yields under similar conditions. Not only monosubstituted Formamides were synthesized from hydroxamic acids, but also N,N-disubstituted Formamides were obtained when secondary amines were used as precursors.
-
Consecutive Lossen rearrangement/transamidation reaction of hydroxamic acids under catalyst- and additive-free conditions
Organic and Biomolecular Chemistry, 2018Co-Authors: Mengmeng Jia, Dimei Chen, Yanmei Chen, Heng Zhang, Yongjia Lin, Yuanzhi XiaAbstract:The Lossen rearrangement is a classic process for transforming activated hydroxamic acids into isocyanate under basic or thermal conditions. In the current report we disclosed a consecutive Lossen rearrangement/transamidation reaction in which unactivated hydroxamic acids were converted into N-substituted Formamides in a one-pot manner under catalyst- and additive-free conditions. One feature of this novel transformation is that the formamide plays triple roles in the reaction by acting as a readily available solvent, a promoter for additive-free Lossen rearrangement, and a source of the formyl group in the final products. Acyl groups other than formyl could also be introduced into the product when changing the solvent to other low molecular weight aliphatic amide derivatives. The solvent-promoted Lossen rearrangement was better understood by DFT calculations, and the intermediacy of isocyanate and amine was supported well by experiments, in which the desired products were obtained in excellent yields under similar conditions. Not only monosubstituted Formamides were synthesized from hydroxamic acids, but also N,N-disubstituted Formamides were obtained when secondary amines were used as precursors.
Wander L. Vasconcelos - One of the best experts on this subject based on the ideXlab platform.
-
Structural evolution of silica sols modified with formamide
Materials Research-ibero-american Journal of Materials, 2001Co-Authors: Rubia F. S. Lenza, Wander L. VasconcelosAbstract:In this work we investigated the influence of formamide on the acid-catalyzed sol-gel process by Fourier transform infrared spectroscopy (FTIR). Three silica sols were studied: Sol catalyzed with nitric acid without formamide, sol catalyzed with nitric acid containing formamide and sol catalyzed with a mixture of nitric acid and hydrofluoric acid and modified with formamide. Following the time evolution of both the Si-(OH) stretching vibration at around 950 cm-1 and the Si-O-(Si) vibration between 1040 cm-1 and 1200 cm-1 we were able to describe the structural evolution of each sol. The curve of evolution of Si-(OH) stretching vibration corresponding to sol A has a simple asymptotic evolution. In the case of formamide containing sol, we observed a two-step structural evolution indicating that for the system containing formamide the polymerization goes through a temporary stabilization of oligomers, which can explain the non-variation of the Si-O(H) bond wavenumber for a certain time. Gelation times were of several days for gels without formamide and few hours for gels containing additive. The presence of additive resulted in a highly interconnected gel.
-
preparation of silica by sol gel method using formamide
Materials Research-ibero-american Journal of Materials, 2001Co-Authors: Rubia F. S. Lenza, Wander L. VasconcelosAbstract:In this work we obtained microporous and mesoporous silica gels by sol-gel processing. Tetraethylortosilicate (TEOS) was used as precursor. Nitric acid and hydrofluoric acid were used as catalysts. In order to study the affect of formamide as drying additive, we used a molar ratio alkoxide/formamide of 1/1. The performance of formamide in obtaining crack-free gels was evaluated through monolithicity measurements. The structural evolution occurring in the interconnected network of the gels during thermal treatment was monitored by Fourier transform infrared spectroscopy (FTIR), shrinkage and density measurements and nitrogen gas sorption. We noted that in the presence of formamide, the Si-O-Si bonds are stronger and belong to a more cross-linked structure. The samples obtained in the presence of formamide have larger pore volume and its pore structure is in the range of mesoporosity. The samples obtained without additive are microporous. Formamide allowed the preparation of crack-free silica gels stabilized at high temperatures.
Yuanzhi Xia - One of the best experts on this subject based on the ideXlab platform.
-
Consecutive Lossen rearrangement/transamidation reaction of hydroxamic acids under catalyst- and additive-free conditions
Organic and Biomolecular Chemistry, 2018Co-Authors: Mengmeng Jia, Dimei Chen, Yanmei Chen, Heng Zhang, Yongjia Lin, Yuanzhi XiaAbstract:The Lossen rearrangement is a classic process for transforming activated hydroxamic acids into isocyanate under basic or thermal conditions. In the current report we disclosed a consecutive Lossen rearrangement/transamidation reaction in which unactivated hydroxamic acids were converted into N-substituted Formamides in a one-pot manner under catalyst- and additive-free conditions. One feature of this novel transformation is that the formamide plays triple roles in the reaction by acting as a readily available solvent, a promoter for additive-free Lossen rearrangement, and a source of the formyl group in the final products. Acyl groups other than formyl could also be introduced into the product when changing the solvent to other low molecular weight aliphatic amide derivatives. The solvent-promoted Lossen rearrangement was better understood by DFT calculations, and the intermediacy of isocyanate and amine was supported well by experiments, in which the desired products were obtained in excellent yields under similar conditions. Not only monosubstituted Formamides were synthesized from hydroxamic acids, but also N,N-disubstituted Formamides were obtained when secondary amines were used as precursors.