- Insight into the Alkaline Stability of N-Heterocyclic Ammonium Groups for Anion-Exchange Polyelectrolytes
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The alkaline stability of N-heterocyclic ammonium (NHA) groups is a critical topic in anion-exchange membranes (AEMs) and AEM fuel cells (AEMFCs). Here, we report a systematic study on the alkaline stability of 24 representative NHA groups at different hydration numbers (λ) at 80 °C. The results elucidate that γ-substituted NHAs containing electron-donating groups display superior alkaline stability, while electron-withdrawing substituents are detrimental to durable NHAs. Density-functional-theory calculations and experimental results suggest that nucleophilic substitution is the dominant degradation pathway in NHAs, while Hofmann elimination is the primary degradation pathway for NHA-based AEMs. Different degradation pathways determine the alkaline stability of NHAs or NHA-based AEMs. AEMFC durability (from 1 A cm?2 to 3 A cm?2) suggests that NHA-based AEMs are mainly subjected to Hofmann elimination under 1 A cm?2 current density for 1000 h, providing insights into the relationship between current density, λ value, and durability of NHA-based AEMs.
- Chen, Nanjun,Fan, Jiantao,Hu, Chuan,Jin, Yiqi,Lee, Young Moo,Li, Hui,Liu, Haijun,Wu, Bo,Xu, Shaoyi
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supporting information
p. 19272 - 19280
(2021/07/25)
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- Hydrogen bonded calixarene capsules kinetically stable in DMSO
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Half-life times up to 4 days in DMSO at room temperature are observed for the decomposition of dimeric capsules of urea substituted calix[4]arenes held together by a combination of hydrogen bonds, mechanical entanglement and cation-π interactions.
- Vysotsky,Thondorf,Boehmer
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p. 1890 - 1891
(2007/10/03)
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- Orthoamides. LIV. Contributions to the chemistry of azavinylogous orthoformic acid amide derivatives
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The azavinylogous aminalester 3 reacts with primary amines to give amidines 5 and 6. In the reaction of 3 with aniline the azavinylogous amidine 7 is produced additionally to the amidine 5c. Ethylendiamine is formylated at both aminogroups, the bis-amidine 8 thus formed is transformed to the salts 9a,b. Benzoxazole and benzimidazole can be prepared from 3 and o-aminophenol and o-phenylenediamine, resp. Carboxylic acid amides, urea, thiourea, aromatic acid hydrazides 17 and the sulfonylhydrazide 19 are formylated by 3 at nitrogen to give N-acylated formamidines 14, 16, 18, 20. From 3 and aliphatic acid hydrazides 17 and alkylhydrazines, resp., can be obtained 1,2,4-triazole 21 and 1-alkyl-1,2,4-triazoles 22a,b, resp. N.N-Dimethylcyanacetamide (32) reacts with 3 and the orthoamide 4a, resp., to give a mixture of the formylated compound 34 and the amidine 33. The reaction conditions are of low influence on the ratio in which 33 and 34 are formed. The orthoamide 4b and 32 react to afford a mixture of the amidine 35 and the enamine 36. Hydrogen-sulfide acts on 3 giving N,N-dimethylthioformamide (37). From 3 and 1-alkynes 41 can be prepared the amidines 42. Hydrolysis of 42b affords phenylpropiolaldehyde (43). The alkylation of the aminalester 3 gives rise to the formation of vinylogous amidinium salts 1c and 1d, resp., additionally is formed the amide acetal 2a. The salt 1d can also be prepared from 3 and borontrifluoride-ether. Iodide reacts with N,N-dimethylformamide acetals 12a,b in an unclear, complicated manner giving orthoesters 53, N,N-dimethylformamide, alkyliodides, alcohols, ammonium iodides 46 and carbondioxide. The action of halogens on 3 affords the salts 1a,b,c,e,f depending on the chosen stoichiometric ratio. Aromatic aldehydes are suited for trapping azavinylogous carbenes formed on thermolysis of 3; 1,3-oxazoles 69 are the reaction products. From 3 and propionaldehyde the amidine 65 can be obtained with low yield. Carbondisulfide transforms 3 to the azavinylogous salt 66. The preparation of the azavinylogous orthoamide 4a is described. The thermolysis of 3 and 4a, resp., gives rise to the formation of the triaminopyrimidine 67. Treatment of 1a with lithium diisopropylamide affords the triaminopyrazine 68, which can also be obtained by thermolysis of 3 in the presence of sodium hydride. Azavinylogous carbenes are thought to be the intermediates. Wiley-VCH Verlag GmbH, 2000.
- Kantlehner, Willi,Hauber, Michael,Haug, Erwin,Schallenmueller, Claus,Regele, Claudia
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p. 682 - 699
(2007/10/03)
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- REACTION OF CYCLIC PARTIAL PHOSPHITE ESTERS WITH ENAMINES - AN ELECTROPHILIC FORM OF THE PUDOVIK REACTION
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It was established that the ease of noncatalytic addition of cyclic and acyclic partial phosphites to enamines is due to the H-donor capacity of the acids and to the degree of localization of the electron density at the C=C bond in the unsaturated partner.It was shown that cyclic phosphites add initially at the carbon-carbon multiple bond of the conjugated N-C=C-C=O system of enamino ketones with the final formation of bisphosphorylated derivatives.
- Safina, Yu. G.,Malkova, G. Sh.,Cherkasov, R. A.
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p. 562 - 574
(2007/10/02)
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- Alkylation and Sulfenylation of Amino Thioethers. Tetrahydro-1,3-thiazine and Related Compounds
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Reactions of electrophiles with several amino thioethers of varying chain length and ring structure are described.The reactants include N,N-dimethylmethanesulfenamide, thio>methane, 1-(N,N-dimethylamino)-2-(methylthio)ethane, tetrahydro-1,3-thiazine, tetrahydro-2-methyl-1,3-thiazine, and the corresponding N-methyl and N-acetyl derivatives.Electrophiles include methyl iodide, ethyl iodide, 3-chloro- and 3-bromopropene, trimethyloxonium fluoroborate, methanesulfenyl chloride, and dimethyl(methylthio)sulfonium fluoroborate.The objective was to assess the influence of one heteroatom on the other in competition for an electrophile.The conditions of S-N, S-C, and N-C cleavage, and attack at sulfur as opposed to nitrogen, are described.
- Kim, Jhong K.,Souma, Yoshie,Beutow, Norman,Ibbeson, Chris,Caserio, Marjorie C.
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p. 1714 - 1720
(2007/10/02)
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- Substituted thiazoles as immunoregulants
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Thiazole derivatives have been made, for example, by reacting a 2-aryl-2,2-dialkoxyethylamine with an appropriately substituted aryl acetyl halide followed by treating the resulting amide with diphosphoryl pentasulfide. The thiazole derivatives are found to be effective immunoregulants.
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- 2(3H)- AND 2(5H)-FURANONES. III. AN EFFICIENT SYNTHESIS AND THE ESCHENMOSER-MANNICH REACTION OF N-SUBSTITUTED 4-AMINO-2(5H)-FURANONE
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A series of N-substituted 4-amino-2(5H)-furanones (II) was derived from β-tetronic acid (I) by direct action of several aliphatic and aromatic amines.The Eschenmoser-Mannich reaction of II readily gave the corresponding Mannich bases (VI) quantitatively.
- Momose, Takefumi,Toyooka, Naoki,Nishi, Takafumi,Takeuchi, Yumi
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p. 1907 - 1924
(2007/10/02)
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- Pyrylium Compounds. XXIII. 2-Dialkylamino-2H-pyrans from Tetra- and Pentasubstituted Pyrylium Salts
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Tetra- and pentasubstituted pyrylium salts of type 6 react with secondary alkyl amines to give stable crystalline 2-dialkylamino-2H-pyrans 7.In the case of tetrasubsituted pyrylium salts 6, R' = Me, R'' = H the reaction occurs regioselectively leading to 2H-pyrans with Me at C-3 of the heterocyclic ring.The structure of the reaction products was established by n.m.r., i.r., u.v. and mass spectroscopic methods.Electrophilic agents like protons, carboxylic acid chlorides or methyl iodide regenerate the original pyrylium cations from 7.In refluxing methanol 7a is converted into the 2-methoxy-2H-pyran derivative 8, whereas in aqueous acetone the pseudobase 9 and with ammonia the pyridine 10 are formed.Reaction of 7a with nitromethane or ethyl cyanoacetate provides the benzene derivatives 11 and 12, respectively.
- Fischer, Gerhard W.,Zimmermann, Thomas,Weissenfels, Manfred
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p. 657 - 666
(2007/10/02)
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- SPECIFICALLY DEUTERATED AND TRITIATED AUXINS
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Regiospecific synthesis of monodeuterated and monotritiated natural auxin (indole-3-acetic acid), a synthetic auxin (naphthalene-1-acetic acid) and a photoaffinity labeling auxin (5-azidoindole-3-acetic acid) are described.These synthesis provide benzene-ring tritiated auxins for use in reversible and covalent binding studies. - Key Word Index: Auxin; azido auxin; indole-3-acetic acid; 5-azidoindole-3-acetic acid; napthalene-1-acetic acid; radiolabeling; photoaffinity labeling; synthesis.
- Melhado, L. Lee,Pearce, Cedric J.,d'Alarcao, Marc,Leonard, Nelson J.
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p. 2879 - 2886
(2007/10/02)
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- Synthesis of Dihydrobenzofurans from Phenolic Mannich Bases and their Quaternized Derivatives
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Reaction of dimethylsulphoxonium methylide with quaternized derivatives of phenolic Mannich bases, and in certain cases with the bases themselves, constitutes a useful synthesis of dihydrobenzofurans.On the other hand treatment of those same quaternized derivatives with diazomethane may be a useful alternative procedure for the preparation of coumarans with base-sensitive groups.
- Blade-Font, Artur,Rocabayera, Teodoro de Mas
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p. 841 - 848
(2007/10/02)
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- AN UNUSUAL REACTION OF TERRAMYCIN WITH METHYL IODIDE
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An unusual fragmentation reaction was observed when terramycin is treated with MeI in acetone at room temp.The reaction proceeds with quaternization, loss of trimethylamine, fission of bonds 4a,5 and 12,12a with formation of an aldehydo-lactone derived from rings B, C and D.Additionally some transformations of this lactone are described.
- Woodward, Robert B.,Zimmerman, Howard E.
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p. 311 - 314
(2007/10/02)
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- Group Transfer Reactions. - Tetracarbonylferrates from Orthoformic Acid Derivatives and Pentacarbonyliron
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The nucleophilic leaving group X is transferred from orthoformic acid derivatives HC(NR2)X (X= NR2, OR, CN) to Fe(CO)5.No such reactions were observed between 4 and amide acetals (HCX2NR2) or ortho ester derivatives HCX3 (X= OR, SR).The structures of the transition metal-acyl complexes obtained have been determined by IR and NMR spectra.In the case of the reaction of tris(dimethylamino)methane (3a) with 4 the equilibrium between the resulting amidinium-carbamoyltetracarbonylferrate complex 5a and the starting materials was investigated.The equilibrium is shifted completely in favor of the ionic compound 5a.However, 3a could be isolated by extraction of this solution with an apolar solvent.Alkylation of 5a with triethyloxonium tetrafluoroborate leads to the tetracarbonyliron-carbene complex 13.Reaction of 5a with acrylonitrile or methyl acrylate by addition of both the nucleophile "NR2-" and the electrophile + and subsequent eliminations gives the β-dimethylamino substitution product 18 and 21, respectively.In contrast 3a induces polymerisation of acrylonitrile.
- Daub, Joerg,Hasenhuendl, Adelheid,Krenkler, Karl P.,Schmetzer, Johannes
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p. 997 - 1015
(2007/10/02)
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