Acetonitrile base catalysis

Solvation may also affect leaving group ability so that, for example, fluoride ions are much better solvated in water than in dipolar aprotic solvents. This can affect the nature of the ratedetermining step in the overall reaction. Hence, in the reaction of l-fluoro-2,4-dinitrobenzene with secondary amines, nucleophilic attack is rate limiting in water, but in acetonitrile, base catalysis is observed with the second step rate determining [87, 88]. 

Wallerberg et al. (1971) conducted the reaction of imidazole and PNPA in acetonitrile containing 1 M water and evaluated the influence of added tetramethylammonium benzoate. The observed rate constant is given by (27) which indicates the contribution of general-base catalysis. Since k2 (1.0 M-2... 

Ion exchange resins are used widely as heterogeneous catalysts of processes that require acid or base catalysis, for example, hydration of propylene to isopropanol, reaction of isobutylene with acetonitrile, and many others. The same kind of equipment is suitable as for ion exchange, but usually regeneration is not necessary, although some degradation of the resin naturally occurs over a period of time. 

Neuvonen H. Kinetics and mechanisms of reactions of pyridines and imidazole with phenyl acetates and trifluoroacetates in aqueous acetonitrile with low content of water nucleophilic and general base catalysis in ester hydrolysis. J Chem Soc Perkin Trans II 1987 266 159-67. 

Such reactions are formally the reverse of the alkylation of cobalt(I) nucleophiles by suitably activated olefins (Eqn. 8). Indeed, Schrauzer et al. [53] have presented spectroscopic as well as other evidence that for cobaloximes where X = —CN or —COOCH2CH3 these reversible reactions proceed via intermediate formation of a cobaloxime(I)-olefin w complex, i.e. the microscopic reverse of Eqns. 10 and 11. However, Barnett et al. [73] have studied the kinetics of the analogous base-catalyzed elimination of 2-cyanoethylcobalamin to produce cob(I)alamin and acrylonitrile. These authors found no general base catalysis and a rate law which was first order in organocobalamin and first order in hydroxide ion and determined a second-order rate constant of 230/M/min. As these authors pointed out, this rate constant is several orders of magnitude greater than the second-order rate constant for ionization of acetonitrile so that the mechanism must either by a concerted E2 elimination (or possibly direct elimination of hydridocobalamin) or, if stepwise, the rate of /8-proton dissociation must be substantially enhanced by the cobalt-containing substituent. 

The specific acid is defined as the protonated form of the solvent in which the reaction is being performed. For example, in water the specific acid is hydronium. In acetonitrile, the specific acid is CHaCNHh and in DMSO the specific acid is CHaSOlH )CH3. The specific base is defined as the conjugate base of the solvent. As examples, in water, acetonitrile, and DMSO, the specific bases would be hydroxide, CH2CN, and CH3SOCH2, respectively. These definitions lead to strict definitions for specific catalysis. Specific-acid catalysis refers to a process in which the reaction rate depends upon the sjrecific acid, not upon other acids in the solution. Specific-base catalysis refers to a process in which the reaction rate depends upon the specific base, not upon other bases in the solution. To understand the kinds of reaction mechanisms that would depend only upon the specific add or base, we need to examine some possible mechanisms and the associated kinetic analyses. 

A study of imidazolysis of 4-nitrophenyl acetate in water, acetonitrile, propylene carbonate, and dioxane at different temperatures concluded that two competitive pathways operate, the bimolecular nucleophilic substitution of the phenol moiety by imidazole and general-base catalysis by a second imidazole molecule. ... 

For the sake of comparison and mutual validation of methods for measuring large follow-up reaction rate constants, it is interesting to apply different methods to the same system. Such a comparison between high-scan-rate ultramicroelectrode cyclic voltammetry, redox catalysis, and laser flash photolysis has been carried out for the system depicted in Scheme 2.25, where methylacridan is oxidized in acetonitrile, generating a cation radical that is deprotonated by a base present in the reaction medium.20... 

A mechanistic study of acetophenone keto-enol tautomerism has been reported, and intramolecular and external factors determining the enol-enol equilibria in the cw-enol forms of 1,3-dicarbonyl compounds have been analysed. The effects of substituents, solvents, concentration, and temperature on the tautomerization of ethyl 3-oxobutyrate and its 2-alkyl derivatives have been studied, and the keto-enol tautomerism of mono-substituted phenylpyruvic acids has been investigated. Equilibrium constants have been measured for the keto-enol tautomers of 2-, 3- and 4-phenylacetylpyridines in aqueous solution. A procedure has been developed for the acylation of phosphoryl- and thiophosphoryl-acetonitriles under phase-transfer catalysis conditions, and the keto-enol tautomerism of the resulting phosphoryl(thiophosphoryl)-substituted acylacetonitriles has been studied. The equilibrium (388) (389) has been catalysed by acid, base and by iron(III). Whereas... 

The cooperative catalysis of CpRu(PPh3)2(CH3CN)PF6 (18) and DBU has permitted chemoselective nucleophilic activation of acetonitrile in the presence of base-sensitive aldehydes to afford corresponding /1-hydroxynitriles (19) in good yield (Scheme... 

Finally, an aspartic acid residue is necessary for full catalysis and this residue is thought to use its CO2 group as a general base. A chemical model shows that the hydrolysis of p-nitrophenyl acetate in aqueous acetonitrile containing sodium benzoate and imidazole follows the rate law ... 

Simplified nucleoside synthesis,8 The known synthesis of nucleosides from silylated heterocycles and a protected sugar derivative in the presence of (CHjijSiClO or (CH3)3SiOTf (6, 639-640) has been adapted to a one-pot synthesis based on in situ silylation and Lewis acid catalysis. The reagent (1) is prepared in situ (equation I) and is added to the free base and acylated sugar then triflic acid, potassium nonaflate, or SnCl4 is added as catalyst. The last Lewis acid is fhe most active and allows condensation to proceed at 24°. Acetonitrile is the most useful solvent. The method is generally applicable and yields are about the same as those obtained in the two-step procedure. 

PCp-CgH Cl) -j results in the quantitative production of -(py)Ru-(bpy)2N0J+ on the surface. The acid-base and redox steps are key elements in the catalytic sequence in Scheme 2. Oxidation of -(py)RuII(bpy>2N02+ to Ru1 in acetonitrile containing the phosphine, acetate ion, and a little water resulted in sustained catalytic currents although the catalysis is not persistent because of slow solvolysis of the nitro group to give -(py)Ru(bpy)2(013-CN) 2+. 

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