- Efficient method for varying the anions in quaternary onium halides
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Quaternary onium salts of halides can be efficiently converted into the corresponding quaternary onium salts of various anions [NO3 -, BF4-, PF6-, CF 3SO3-, CH3SO3 -, ClO4-, p-CH3C6H 4SO3-, CF3CO2 -, 2,4-(NO2)2C6H3O -] by treating the onium halide with trimethyl phosphate under neat condition in the presence of an equivalent amount of conjugate acid of the desired anion.
- Jeon, Jong Yeob,Varghese, Jobi Kodiyan,Park, Ji Hae,Lee, Suck-Hyun,Lee, Bun Yeoul
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- Ambident Reactivity of Phenolate Anions Revisited: A Quantitative Approach to Phenolate Reactivities
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Prompted by the observation that the regioselectivities of phenolate reactions (C versus O attack) are opposite to the predictions by the principle of hard and soft acids and bases, we performed a comprehensive experimental and computational investigation of phenolate reactivities. Rate and equilibrium constants for the reactions of various phenolate ions with benzhydrylium ions (Aryl2CH+) and structurally related quinone methides have been determined photometrically in polar aprotic solvents. Quantum chemical calculations at the SMD(MeCN)/M06-2X/6-31+G(d,p) level confirmed that O attack is generally favored under kinetically controlled conditions, whereas C attack is favored under thermodynamically controlled conditions. Exceptions are diffusion-limited reactions with strong electrophiles, which give mixtures of products arising from O and C attack, as well as reactions with metal alkoxides in nonpolar solvents, where oxygen attack is blocked by strong ion pairing. The Lewis basicity (LB) and nucleophilicity (N, sN) parameters of phenolates determined in this work can be used to predict whether their reactions with electrophiles are kinetically or thermodynamically controlled and whether the rates are activation- or diffusion-limited. Comparison of the measured rate constants for the reactions of phenolates with carbocations with the Gibbs energies for single-electron transfer manifests that these reactions proceed via polar mechanisms.
- Mayer, Robert J.,Breugst, Martin,Hampel, Nathalie,Ofial, Armin R.,Mayr, Herbert
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p. 8837 - 8858
(2019/07/08)
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- Delineation of the Critical Parameters of Salt Catalysts in the N-Formylation of Amines with CO2
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N-formylation of amines combining CO2 as a C1 source with a hydrosilane reducing agent is a convenient route for the synthesis of N-formylated compounds. A large number of salts including ionic liquids (ILs) have been shown to efficiently catalyze the reaction and, yet, the key features of the catalyst remain unclear and the best salt catalysts for the reaction remain unknown. Here we demonstrate the detrimental effect of ion pairing on the catalytic activity and illustrate ways in which the strength of the interaction between the ions can be reduced to enhance interactions and, hence, reactivity with the substrates. In contrast to the current hypothesis, we also show that salt catalysts are more active as bases rather than nucleophiles and identify the pKa where the nucleophilic role of the catalyst switches to the more active basic role. The identification of these critical parameters allows the optimum salt catalyst and conditions for an N-formylation reaction to be predicted.
- Hulla, Martin,Ortiz, Daniel,Katsyuba, Sergey,Vasilyev, Dmitry,Dyson, Paul J.
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supporting information
p. 11074 - 11079
(2019/07/17)
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- A highly active and recyclable catalytic system for CO2/propylene oxide copolymerization
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(Figure Presented) Converting CO2 into polymer: A catalytic system that produces a high molecular weight CO2/propylene oxide copolymer with high activity and selectivity is disclosed. After filtration through silica gel, elution of the catalyst leaves a solid phase with a negligible metal residue (see picture). The catalyst can be reused without significant loss of performance.
- S, Sujith,Min, Jae Ki,Seong, Jong Eon,Na, Sung Jea,Lee, Bun Yeoul
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supporting information; experimental part
p. 7306 - 7309
(2009/04/10)
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- ACID DEACTIVATION OF A NUCLEOPHILE IN THE PHASE-TRANSFER PHENOLYSIS OF CYCLOPHOSPHAZENES AND ITS MECHANISM UNDER HOMOGENEOUS CONDITIONS
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The reactions of tetraalkylammonium salts of 2,4-dinitrophenol (ArO-Q+) with the cyclic trimer of phosphonitrile chloride were studied in a two-phase system of a buffer solution and benzene and in a homogeneous system modeling the conditions of the organic phase. In a two-phase system the aryloxide ion, while being incompletely ionized in the aqueous phase, is extracted into the organic phase together with the neutral form of the phenol, which results in the inhibition of the reaction of monoaryloxyphosphazene formation. The reason lies in the deactivation of the nucleophile as a result of the formation of less reactive complexes with an H bond between the anion and/or the ion pair ArO-Q+ and the proton donor (ROH) contained in the organic phase. On the basis of the kinetic relations and of the results of a study of the equilibrium processes it was found that in the case of strong proton donors (phenols) complexes of the anion and of the ion pair ArO-Q+ with a composition of 1:1 react with the substrate, but in case of weak donors (alcohols) an ion pair not bound into a complex and associations with the anion with compositions of 1:1 and 1:2 react. The reactivity of the complexes of composition 1:1 is thus proportional to the values of the constants of complex formation with ROH, and the inhibiting action of the latter is governed by a single correlation equation without regard to the type of the H-bond acceptor and to the nature of ROH. On the basis of the quantum-chemical calculations it was supposed that the ambiguous effect of ROH on the nucleophilicity of the anions and of the ArO-Q+ ion pairs is determined by the differences in specific solvation between the transition states of the reactions involving these forms of the reagent.
- Afon'kin, A. A.,Shumeiko, A. E.,Popov, A. F.
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p. 457 - 463
(2007/10/02)
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