- Polyamide synthesis from 6-aminocapronitrile, part 2: Heterogeneously catalyzed nitrile hydrolysis with consecutive amine amidation
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To test the potential of heterogeneous catalysts for the nylon-6 synthesis from 6-aminocapronitrile, a number of zeolites, aluminum silicate, and metal oxides were tested as catalysts for the model reaction of pentanenitrile with water and hexylamine to N-hexylpentanamide. All zeolitic and aluminum silicate systems showed an insufficient performance, while the metal oxides (TiO 2, ZrO2, Nb2O5) showed very promising results. The kinetic behavior of the metal oxides was further investigated. First the nitrile was catalytically hydrolyzed to the terminal amide and subsequently the amidation of the hexylamine occurred. To polymerize 6-aminocapronitrile into nylon-6, more than 99% nitrile conversion was required to obtain a high-molecular-weight polymer. Pentanenitrile conversions larger than 99% can be obtained within six hours, at 230°C, by using ZrO 2 as the catalyst. A kinetic study (by using IR spectroscopy) on the behavior of the metal oxides demonstrated that the adsorbed nitrile was catalytically hydrolyzed at the surface, but remained tightly bound to the surface. Zirconia-catalyzed polymerizations of 6-amino-capronitrile demonstrated that high-molecular-weight nylon-6 is feasible by using this route.
- Van Dijk, Adrianus J.M.,Duchateau, Robbert,Hensen, Emiel J.M.,Meuldijk, Jan,Koning, Cor E.
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- Effect of a hydrophobic environment on the hydrogen exchange kinetics of model amides determined by 1H-NMR spectroscopy
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In proteins, backbone amide hydrogen exchange rates can reveal important information about protein structure and dynamics. In order to assess the possible effects of detergent on the hydrogen exchange rates of detergentsolubilized proteins, we have synthesized a series of model aliphatic amides and measured their amide proton exchange rates in water and sodium dodecyl sulfate (SDS) micelles. Hydrogen exchange was measured using steady-state saturation-transfer proton nuclear magnetic resonance (NMR) spectroscopy. The extent of interaction of the model compounds with SDS was determined by measuring the longitudinal relaxation times, chemical shifts, and temperature coefficients of the amide protons. The sensitivity of the amide proton chemical shift to hydrogen bonding was found to be a particularly useful indicator of the extent of interaction of the amides with the hydrophobic core of the micelle. It is argued that the measured hydrogen exchange parameters reflect the dynamics of exchange of the molecules between bulk solvent and the surface and core of the micelle. Two major effects of the micelle on hydrogen exchange were measured: First, an electrostatic effect due to the negatively charged sulphate groups of SDS causes a decrease of the local pH at the micellar surface. This effect increases with the affinity of the amides for the micelle and enhances acid-catalyzed exchange and decreases base-catalyzed exchange. Second, a hydrophobic effect of the core of the micelle causes a depression of the minimum rate of exchange, which, for the most nonpolar molecule, is 25-fold. This effect is similar in magnitude to the slowing of exchange by hydrogen bonding reported by Perrin et al. (J. Am. Chem. Soc. 1990, 112, 3122-3125). The hydrophobic effect is likely to be an important factor in the slowing of exchange in the solvent-excluded interior of water-soluble proteins as well as in the exchange of detergent-solubilized peptides and proteins.
- Spyracopoulos, Leo,O'Neil, Joe D. J.
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- Polyamide synthesis from 6-aminocapronitrile, part 1: N-alkyl amide formation by amine amidation of a hydrolyzed nitrile
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The synthesis of N-hexylpentanamide from a stoichiometric amount of pentanenitrile and hexylamine has been studied as a model reaction for the synthesis of nylon-6 from 6-aminocapronitrile. The reaction was carried out under mild hydrothermal conditions and in the presence of a homogeneous ruthenium catalyst. For the mild hydrothermal conditions the presence of hexylamine distinctively increases the nitrile hydrolysis compared to the nitrile hydrolysis in the absence of hexylamine. Amine-catalyzed nitrile hydrolysis mainly produces the N-substituted amide. A clear product development is observed, consisting of first the terminal amide formation and second the accumulation of N-hexylpentanamide. With a maximum conversion of only 80 % after 18 h, the nitrile hydrolysis rate at 230°C is still much too low for nylon-6 synthesis. Ruthenium dihydride phosphine was therefore used as a homogeneous catalyst, which significantly increases the nitrile hydrolysis rate. At a temperature of 140°C and with only 0.5 mol% [RuH2-(PPh 3)4]a 60% nitrile conversion is already reached within 2 h. Initially the terminal amide is the sole product, which is gradually converted into N-hexylpentanamide. The reaction has a high initial rate, however, for higher conversions a strong decrease in hydrolysis rate is observed. This is ascribed to product inhibition, which results from the equilibrium nature of the reaction.
- Van Dijk, Adrianus J.M.,Heyligen, Tom,Duchateau, Robbert,Meuldijk, Jan,Koning, Cor E.
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- Manganese-Catalyzed Direct Conversion of Ester to Amide with Liberation of H2
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A simple and efficient Mn-catalyzed acylation of amines is achieved using both acyl and alkoxy functions of unactivated esters with the liberation of molecular hydrogen as a sole byproduct. The present protocol provides an atom-economical and sustainable route for the synthesis of amides from esters by employing an earth-abundant manganese salt and inexpensive phosphine-free tridentate ligand.
- Mondal, Akash,Subaramanian, Murugan,Nandakumar, Avanashiappan,Balaraman, Ekambaram
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supporting information
p. 3381 - 3384
(2018/06/11)
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- N-Acyl-N-(4-chlorophenyl)-4-nitrobenzenesulfonamides: Highly selective and efficient reagents for acylation of amines in water
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A variety of N-acyl-N-(4-chlorophenyl)-4-nitrobenzenesulfonamides (1a-e) were synthesized in one pot from 4-chloroaniline under solvent-free conditions and have been developed as chemoselective N-acylation reagents. Selective protection of primary amines in the presence of secondary amines, acylation of aliphatic amines in the presence of aryl amines, and monofunctionalization of primary-secondary diamines as well as selective N-acylation of amino alcohols using these reagents are described. All of the acylation reactions were carried out in water as a green solvent. High stability and easy preparation of these acylating reagents are other advantages of this method.
- Ebrahimi, Sara,Saiadi, Safoura,Dakhilpour, Simin,Mirsattari, Seyed Nezamoddin,Massah, Ahmad Reza
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- Chemo- and regioselective homogeneous rhodium-catalyzed hydroamidomethylation of terminal alkenes to N-alkylamides
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A rhodium/xantphos homogeneous catalyst system has been developed for direct chemo- and regioselective mono-N-alkylation of primary amides with 1-alkenes and syngas through catalytic hydroamidomethylation with 1-pentene and acetamide as model substrates. For appropriate catalyst performance, it appears to be essential that catalytic amounts of a strong acid promoter, such as p-toluenesulfonic acid (HOTs), as well as larger amounts of a weakly acidic protic promoter, particularly hexafluoroisopropyl alcohol (HORF) are applied. Apart from the product N-1-hexylacetamide, the isomeric unsaturated intermediates, hexanol and higher mass byproducts, as well as the corresponding isomeric branched products, can be formed. Under optimized conditions, almost full alkene conversion can be achieved with more than 80 % selectivity to the product N-1-hexylamide. Interestingly, in the presence of a relatively high concentration of HORF, the same catalyst system shows a remarkably high selectivity for the formation of hexanol from 1-pentene with syngas, thus presenting a unique example of a selective rhodium-catalyzed hydroformylation-hydrogenation tandem reaction under mild conditions. Time-dependent product formation during hydroamidomethylation batch experiments provides evidence for aldehyde and unsaturated intermediates; this clearly indicates the three-step hydroformylation/condensation/hydrogenation reaction sequence that takes place in hydroamidomethylation. One likely role of the weakly acidic protic promoter, HORF, in combination with the strong acid HOTs, is to establish a dual-functionality rhodium catalyst system comprised of a neutral rhodium(I) hydroformylation catalyst species and a cationic rhodium(III) complex capable of selectively reducing the imide and/or ene-amide intermediates that are in a dynamic, acid-catalyzed condensation equilibrium with the aldehyde and amide in a syngas environment. Taking control: A rhodium/xantphos homogeneous catalyst system has been developed for direct chemo- and regioselective mono-N-alkylation of primary amides with 1-alkenes and syngas through the new catalytic hydroamidomethylation reaction (see picture). Copyright
- Raoufmoghaddam, Saeed,Drent, Eite,Bouwman, Elisabeth
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p. 1759 - 1773
(2013/10/21)
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- Rhodium-catalyzed homogeneous reductive amidation of aldehydes
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The catalytic reductive amidation of an aldehyde (hexanal) with an amide (acetamide) is reported. Apart from the desired N-hexylacetamide, the two isomeric unsaturated intermediates as well as hexanol are produced together with higher mass products that arise from aldol condensation and diamide coupling of the aldehyde. Screening of different catalyst precursor salts, ligands and reaction conditions led to the finding that the catalytic system based on the (cyclooctadiene)rhodium chloride dimer, [Rh(cod)Cl]2, in combination with the ligand xantphos and an acid co-catalyst results in high selectivity for the desired product. Under optimized conditions nearly full conversion is reached with high selectivity to the desired N-alkylamide and with a very high N-alkylamide/alcohol ratio, while producing only small amounts of by-products. The scope of the reaction has been investigated using different amides as well as aldehydes; the results show the general applicability of this novel reaction, but with electron-withdrawing amides the selectivity to N-alkylamide is lower. NMR studies showed that the nucleophilic addition of acetamide to hexanal is acid catalyzed, forming N-(1-hydroxyhexyl)acetamide in equilibrium with both hexanal and the dehydrated unsaturated imides. A catalytic mechanism is proposed in which a strong acid such as HOTs acts as a co-catalyst by establishing a rapid chemical equilibrium between the aldehyde, acetamide and the intermediates. Furthermore, it is proposed that the presence of acid causes a change in catalytic species, enabling a cationic Rh/xantphos hydrogenation catalyst to selectively hydrogenate the intermediates to N-hexylacetamide in the presence of hexanal. Copyright
- Raoufmoghaddam, Saeed,Drent, Eite,Bouwman, Elisabeth
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supporting information
p. 717 - 733
(2013/04/23)
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- Direct synthesis of imines from alcohols and amines with liberation of H2
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"Chemical equation presented" A clean sweep: Aryl and aliphatic mines can be synthesized directly and efficiently from alcohols and amines under mild, neutral conditions with the liberation of only molecular hydrogen and water (see scheme; R=isopropyl, tert-butyl). This general, environmentally benign reaction is catalyzed by a de-aromatized ruthenium PNP pincer complex (0.2 mol%), and can proceed in toluene under an inert atmosphere or under air.
- Gnanaprakasam, Boopathy,Zhang, Jing,Milstein, David
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supporting information; experimental part
p. 1468 - 1471
(2010/05/02)
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