- AN ANALYSIS OF COMPLEX ALKYL-SUBSTITUENT EFFECTS IN THE WATER-CATALYZED HYDROLYSIS OF 1-ACYL-1,2,4-TRIAZOLES
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Pseudo-first-order rate constants and thermodynamic activation parameters have been determined for the water-catalyzed hydrolysis of the 1-acyl-1,2,4-triazoles 1-9 in water and in aqueous acetonitrile .The reaction occurs via water-catlalyzed nucleophilic attack of water at the amide carbonyl group.Variation of the alkyl group in the acyl part of the substrate led to the sequence of reactivities (in water): R= t-Bu > i-Pr > Et > Me > n-Pr > s-Bu > i-Pent > neo-Pent.This complex behaviour strogly suggest the operation of a composite steric effect most likely involving contributions from conformational preference (SE1), change of coordination number at carbonyl carbon (SE2), steric repulsion between O2 and the alkyl group (SE3), and steric inhibition of solvation (SE4)> Modelling of the relative rates in water in terms of the expanded branching equation gave satisfactory results.Two pssible transition states are proposed for the neutral hydrolysis, one involving intramolecular hydrogen bonding between the second water molecule and N2 of the 1,2,4-triazole ring .The different sequence of reactivities for neutral hydrolysis in aqueous acetonitrile as well as the rates for hydroxide-ion-catalyzed hydrolysis in water (BAc2 machanism) support the analysis of substituent effects.
- Mooij, Herman J.,Engberts, B. F. N.,Charton, Marvin
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p. 185 - 189
(2007/10/02)
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- Facile Conversions of Carboxylic Acids into Amides, Esters, and Thioesters Using 1,1'-Oxalyldiimidazole and 1,1'-Oxalyldi(1,2,4-triazole)
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Aliphatic, aromatic, and heteroaromatic carboxylic acids react with 1,1'-oxalyldiimidazole (1) or 1,1'-oxalyldi(1,2,4-triazole) (2) in acetonitrile for 40 min at 40 degC to give the corresponding 1-acylazole intermediates (11), which promptly undergo aminolysis and alcoholysis to form amides (13) including dipeptides (14), esters (16), and thioesters (19).These findings show that both 1 and 2 can be utilized as condensing reagents for the synthesis of carboxylic acid derivatives.Keywords --- 1,1'-oxalyldiimidazole; 1,1'-oxalyldi(1,2,4-triazole); 1,1'-carbonyldiimidazole; 1-acylazole; condensing reagent; amidation; esterification; dipeptide; aminolysis; alcoholysis
- Kitagawa, Tokujiro,Kuroda, Hiroko,Sasaki, Hideaki,Kawasaki, Koichi
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p. 4294 - 4301
(2007/10/02)
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