- Aerobic oxidative transformation of primary azides to nitriles by ruthenium hydroxide catalyst
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In the presence of an easily prepared supported ruthenium hydroxide catalyst, Ru(OH)x/Al2O3, various kinds of structurally diverse primary azides including benzylic, allylic, and aliphatic ones could be converted into the corresponding nitriles in moderate to high yields (13 examples, 65-94% yields). The gram-scale (1 g) transformation of benzyl azide efficiently proceeded to give benzonitrile (0.7 g, 90% yield) without any decrease in the performance in comparison with the small-scale (0.5 mmol) transformation. The catalysis was truly heterogeneous, and the retrieved catalyst could be reused for the transformation of benzyl azide without an appreciable loss of its high performance. The present transformation of primary azides to nitriles likely proceeds via sequential reactions of imide formation, followed by dehydrogenation (β-elimination) to produce the corresponding nitriles. The Ru(OH)x/Al2O3 catalyst could be further employed for synthesis of amides in water through the transformation of primary azides (benzylic and aliphatic ones) to nitriles, followed by sequent hydration of the nitriles formed. Additionally, direct one-pot synthesis from alkyl halides and TBAN3 (TBA = tetra-n-butylammonium) could be realized with Ru(OH)x/Al2O3, giving the corresponding nitriles in moderate to high yields (10 examples, 64-84% yields).
- He, Jinling,Yamaguchi, Kazuya,Mizuno, Noritaka
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supporting information; experimental part
p. 4606 - 4610
(2011/07/29)
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- Reactivity of anionic nucleophiles in ionic liquids and molecular solvents
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The nucleophilic reactivity of a representative series of anions has been measured in [hmim][ClO4] 3i, [hm2im][ClO4] 3′i, and [hmim][PF6] 3l ILs in the reaction with n-alkyl methanesulfonates and compared with that found in common molecular solvents (MeOH, DMSO, PhCl). The reactivity is found to depend on both the imidazolium cation-anion interaction and the specific solvation by water present in the IL, the water playing the main effect, in particular with hydrophilic anions. Removal of the largest quantity of water remarkably increases the ion pair reactivity in the IL up to rate constant value k comparable with those obtained in DMSO and in low polarity media (PhCl).
- Betti, Cecilia,Landini, Dario,Maia, Angelamaria
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p. 1689 - 1695
(2008/09/18)
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- Anion nucleophilicity in ionic liquids: A comparison with traditional molecular solvents of different polarity
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The nucleophilic reactivity of a homogeneous series of anions (halides, pseudohalides and organic anions) in the ionic liquids [hexmim] [ClO 4] and [hexmim] [PF6] has been measured in their reaction with n-alkyl methanesulfonates, and compared with that found in traditional molecular solvents of different polarity, that is, chlorobenzene, DMSO, and MeOH.
- Landini, Dario,Maia, Angelamaria
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p. 3961 - 3963
(2007/10/03)
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- Phase-Transfer Reactions Catalyzed by Lipophilic Cryptands and Dicyclohexano-18-crown-6: Dehydrating Effect of Concentrated Aqueous Alkaline Solutions
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A study of how the concentration of aqueous KOH affects the hydration and hence the reactivity of anions (Cl-, Br-, I-, SCN-, N3-) in aliphatic nucleophilic substitutions catalyzed by lipophilic cryptand (1a) and dicyclohexano-18-crown-6 (DCH18C6) (2) under phase-transfer conditions is reported.A comparison with the same reactions performed in classical liquid-liquid PTC and homogeneous anhydrous conditions is also included.Unlike quaternary onium salts, even at the highest KOH concentrations (53percent; ie., conditions in which aH2O ca. 0), water in the presence of 1a is not completely removed.Residual hydration depends on the nature of the anion and is the highest for anions with localized and/or less polarizable charge, such as Cl-, Br-, and N3-.As a consequence, rate constants noticeably increase in comparison with those found under conventional PTC conditions but do not reach those of anhydrous solutions.The different behavior of cryptates and quaternary salts is discussed on the basis of the different topology of the two systems.Behavior of crown ethers is in between that of quaternary salts and cryptates, since residual hydration in the presence of 53percent aqueous KOH is lower than that of cryptates, whereas anionic reactivity becomes practically identical with that found under anhydrous conditions.
- Landini, Dario,Maia, Angelamaria,Montanari, Fernando
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p. 2917 - 2923
(2007/10/02)
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- Nonhydrated Anion Transfer from the Aqueous to the Organic Phase: Enhancement of Nucleophilic Reactivity in Phase-Transfer Catalysis
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A systematic study of how the nature and concentration of the inorganic salt affect hydration and reactivity of anions transferred into the organic phase under conditions of phase-transfer catalysis (PTC) has been performed.The inorganic salt concentration in the aqueous phase up to saturated solution (= or > 6 M), does not affect the hydration and hence the reactivity of the anion in aliphatic nucleophilic substitutions.On the other hand, in concentrated aqueous alkaline solutions (50percent NaOH or 60percent KOH) unhydrated anions are transferred from the aqueous to the organic phase.The anionic reactivity thus becomes identical with that found under anhydrous homogeneous conditions, the rate enhancement being 13.0, 4.0, 2.6, and 1.4 times for Cl(1-), N3(1-), Br(1-), and I(1-), respectively.The same dehydrating effect was not observed with less concentrated alkaline solutions or with 50percent aqueous NaF.These data show the unique property of OH(1-) in producing conditions of virtually null water activity under PTC conditions.
- Landini, Dario,Maia, Angelamaria,Podda, Gianni
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p. 2264 - 2268
(2007/10/02)
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- Crown ethers as phase-transfer catalysts. A comparison of an ionic activation in aqueous-organic two-phase systems and in low polarity anhydrous solutions by perhydrodibenzo-18-crown-6, lipophilic quaternary salts, cryptands
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Anion-promoted nucleophilic substitutions carried out in aqueous-organic two-phase systems in the presence of catalytic amounts of perhydrodibenzo-18- crown-6 follow the classic mechanism of phase-transfer catalysis. The observed pseudo-first-order rate constants are linearly related to the concentration of complexed crown ether in the organic phase. The narrow reactivity range and the sequence found in the reaction between n-octyl methane-sulphonate and a homogeneous series of anions in the PhCl-H2O two-phase system (N 3- > I- ~ Br- > CN - > Cl- > SCN-) remain largely unaltered in anhydrous PhCl. From this point of view complexed crown ethers differ substantially from lipophilic quaternary salts and cryptates. Indeed, removal of the hydration sphere of the anions in going from two-phase to anhydrous conditions is balanced by a larger cation-anion interaction, resulting in a very small variation of anion reactivity. This indicates that, unlike cryptates, complexed crown ethers can hardly be considered as a source of 'naked anions.' A comparison is also reported among lipophilic crown ethers, quaternary salts, and cryptands as phase-transfer catalysts.
- Landini, Dario,Maia, Angelamaria,Montanari, Fernando,Pirisi, Filippo M.
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