- Shape-Selective Recognition of Quaternary Ammonium Chloride Ion Pairs
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Synthetic receptors that recognize ion pairs are potentially useful for many technical applications, but to date there has been little work on selective recognition of quaternary ammonium (Q+) ion pairs. This study measured the affinity of a tetralactam macrocycle for 11 different Q+·Cl- salts in chloroform solution. In each case, NMR spectroscopy was used to determine the association constant (Ka) and the structure of the associated complex. Ka was found to depend strongly on the molecular shape of Q+ and was enhanced when Q+ could penetrate the macrocycle cavity and engage in attractive noncovalent interactions with the macrocycle's NH residues and aromatic sidewalls. The highest measured Ka of 7.9 × 103 M-1 was obtained when Q+ was a p-CN-substituted benzylic trimethylammonium. This high-affinity Q+·Cl- ion pair was used as a template to enhance the synthetic yield of macrocyclization reactions that produce the tetralactam receptor or structurally related derivatives. In addition, a permanently interlocked rotaxane was prepared by capping the end of a noncovalent complex composed of the tetralactam macrocycle threaded by a reactive benzylic cation. The synthetic method provides access to a new family of rotaxanated ion pairs that can likely act as anion sensors, molecular shuttles, or transport molecules.
- Li, Dong-Hao,Smith, Bradley D.
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p. 2808 - 2816
(2019/03/26)
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- Alkali stability excellent imidazole and imidazolium cation
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and membranes and devices comprising the polymers. Also provided are methods of making the inventive compounds and polymers.
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Paragraph 0290-0292
(2018/04/13)
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- Benzylic Ammonium Ylide Mediated Epoxidations
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A high yielding synthesis of stilbene oxides using ammonium ylides has been developed. It turned out that the amine leaving group plays a crucial role as trimethylamine gives higher yields than DABCO or quinuclidine. The amine group also influences the diastereoselectivity, and detailed DFT calculations to understand the key parameters of these reactions have been carried out.
- Roiser, Lukas,Robiette, Rapha?l,Waser, Mario
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supporting information
p. 1963 - 1968
(2016/08/10)
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- Imidazolium Cations with Exceptional Alkaline Stability: A Systematic Study of Structure-Stability Relationships
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Highly base-stable cationic moieties are a critical component of anion exchange membranes (AEMs) in alkaline fuel cells (AFCs); however, the commonly employed organic cations have limited alkaline stability. To address this problem, we synthesized and characterized the stability of a series of imidazolium cations in 1, 2, or 5 M KOH/CD3OH at 80 °C, systematically evaluating the impact of substitution on chemical stability. The substituent identity at each position of the imidazolium ring has a dramatic effect on the overall cation stability. We report imidazolium cations that have the highest alkaline stabilities reported to date, >99% cation remaining after 30 days in 5 M KOH/CD3OH at 80 °C.
- Hugar, Kristina M.,Kostalik, Henry A.,Coates, Geoffrey W.
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supporting information
p. 8730 - 8737
(2015/07/27)
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- Alkylation of ammonium salts catalyzed by imidazolium-based ionic liquid catalysts
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Quaternary ammonium salts were synthesized from ammonium salts and dialkyl carbonates over imidazolium ionic liquid catalysts. The reaction gave almost stoichiometric amounts of the quaternary ammonium salts for halides and nitrates. It was found that the electron-donating property of the alkyl moieties of ammonium cations, the electrophilic nature of the alkyl group of the carbonate, the acidity of the acid that the anion of the ammonium salt corresponds to, and the steric hindrance of the ammonium salts and the dialkyl carbonates are the key factors that influence the yields of quaternary ammonium salts. Strong electron-donating alkyl groups on the nitrogen atom of the ammonium salt, electron-withdrawing groups on the methylene carbon of dialkyl carbonate, and weaker steric hindrance of the starting ammonium salts and dialkyl carbonates favor the alkylation reaction of ammonium salts.
- Zheng, Zhuo Qun,Wang, Jie,Wu, Ting Hua,Zhou, Xiao Ping
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p. 1095 - 1101
(2008/03/27)
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- Apparent molar volumes of benzyltrimethylammonium bromide and its homologs in aqueous solution at 15, 25, and 35°C
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Apparent molar volumes at infinite dilution of benzyltrimethylammonium bromide and its butyl and hexyl homologs at 15, 25, and 35°C and of dibenzyldimethylammonium bromide at 25°C in aqueous solution were estimated from density measurements. The additivity rule for the contribution of the methylene groups to the apparent molar volumes was found to be obeyed within a broad range of homologs, which covers the parent salt and the dodecyldimethylbenzylammonium bromide. The volumetric contribution of the phenylene (-C6H4-) group was estimated to be 61 cm3-mol-1 at 25°C. A value of - 16.9 ± 0.3 cm3-mol-1 was suggested for the volumetric contribution of the N+ fragment to the apparent molar volume of alkylbenzyldimethylammonium salts.
- Tutaj,Gonzalez-Perez,Czapkiewicz,Del Castillo,Rodriguez
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p. 1101 - 1109
(2007/10/03)
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