Relation of the transition-state structure for the water-catalyzed hydrolysis of 1-acetylimidazolium ion to solvent hydrophobicity: proton inventories in water-acetonitrile mixtures

Huskey, W. Phillip; Hogg, John L.

doi:10.1021/jo00314a011

Cited by 8 publications

(1 citation statement)

References 8 publications

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“…3.5 x lo-' and thus K 5. 6 x lo6 (details are in the Experimental section). Equation (xiii) is seen to give only a very approximate guide to values of K for other 2-…”

Section: 99941mentioning

confidence: 99%

Kinetics and equilibria of ring closure through an amide linkage. Part 2. 1-Aryl-2-pyrrolidones

ABDALLAH¹,

Moodie²

1983

J. Chem. Soc., Perkin Trans. 2

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Equilibrium constants, and rate constants for forward and reverse reactions, for ring closure of several 4-(arylamino) butanoic acids to 1 -aryl-2-pyrrolidones in aqueous acid, together with ionisation constants of the former group of compounds, are reported. The equilibrium constants K at 50 "C between neutral protonic forms of open-chain and ring compounds are related to the ionisation constants of the nitrogenprotonated 4-(ary1amino)butanoic acids, K1, by the equation : log K = 0.70 (pK,) + 1.53. The value of K for pyrrolidone itself was measured for comparison. Studies of l80 exchange reveal that (except in the case of the substrate which bears the most electron-withdrawing substituents in the aryl ring, namely 2,4-dinitro) the rate-determining step lies between the tetrahedral intermediate and the ring compound. Substituent effects and solvent deuterium isotope effects on the hydronium-ion catalysed reaction are consistent with a transition state close to the neutral tetrahedral intermediate. The effects of methyl substituents in the heterocyclic ring on rate and equilibrium constants have also been studied. The variation of K with temperature, and derived thermodynamic parameters, are reported in two cases.This study was undertaken in order to clarify certain aspects of the mechanism of amide hydrolysis (the reverse of the title reaction) and to provide information about the stability of five-membered rings.

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“…3.5 x lo-' and thus K 5. 6 x lo6 (details are in the Experimental section). Equation (xiii) is seen to give only a very approximate guide to values of K for other 2-…”

Section: 99941mentioning

confidence: 99%

Kinetics and equilibria of ring closure through an amide linkage. Part 2. 1-Aryl-2-pyrrolidones

ABDALLAH¹,

Moodie²

1983

J. Chem. Soc., Perkin Trans. 2

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ChemInform Abstract: RELATION OF THE TRANSITION‐STATE STRUCTURE FOR THE WATER‐CATALYZED HYDROLYSIS OF 1‐ACETYLIMIDAZOLIUM ION TO SOLVENT HYDROPHOBICITY: PROTON INVENTORIES IN WATER‐ACETONITRILE MIXTURES

Huskey¹,

Hogg²

1981

Chemischer Informationsdienst

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Kinetics of the pH‐independent hydrolyses of 4‐nitrophenyl chloroformate and 4‐nitrophenyl heptafluorobutyrate in water‐acetonitrile mixtures: consequences of solvent composition and ester hydrophobicity

Seoud

Siviero

2006

J of Physical Organic Chem

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The pH-independent hydrolyses of 4-nitrophenyl chloroformate, NPCF and 4-nitrophenyl heptafluorobutyrate, NPFB in aqueous acetonitrile were studied spectrophotometrically from 15 to 45 8C. The binary solvent composition covers water concentrations from 2.349 to 53.207 and from 2.745 to 53.333 mol L À1 for NPCF and NPFB, respectively. For both esters, the dependence of log (k obs ), the observed rate constant, on log [water] is sigmoidal. The approximate kinetic orders with respect to water were found to be 2 and 3 for NPCF and NPFB, respectively. DG 6 ¼ gradually decreases as a function of increasing [water], due to a complex, quasi-mirror image compensation of DH 6 ¼ and DS 6 ¼ ; both parameters increase. The structures of the transition states were probed by a proton inventory study, carried out in the presence of L 2 O mole fractions (L ¼ H or D) of 0.190, 0.540, 0.890 and 0.180, 0.529, 0.890, for NPCF and NPFB, respectively. Plots of observed rate constants versus the atom fraction of deuterium in the solvent curve downward. Cyclic transition state models were fitted to the kinetic data; these models contain the ester and two water molecules (NPCF) or three water molecules (NPFB). Thus, the sigmoidal dependences of log (k obs ) on log [water] are not due to a change in the number of water molecules in the transition states as a function of increasing [water]. The binary solvent mixture is micro-heterogeneous; there exists two ''micro-domains,'' one consists predominantly of coordinated water molecules, the other consists mostly of acetonitrile hydrogen-bonded to water molecules. NPCF is 232 times more soluble in water than NPFB. That is, the former ester is dissolved in the outer, more polar periphery of these micro-domains whereas the more hydrophobic NPFB is dissolved in their inner, less polar interiors. This conclusion is corroborated by comparing the dependence on log [water] of log [k obs ], and of E T , the empirical solvent polarity parameter, as measured by solvatochromic probes of increasing hydrophobicity. a The rate constants reported are the mean of at least triplicate runs. The relative standard deviation between k obs of a triplicate, that is, ((standard deviation/ k obs )100) was 1.0%.

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Relation of the transition-state structure for the water-catalyzed hydrolysis of 1-acetylimidazolium ion to solvent hydrophobicity: proton inventories in water-acetonitrile mixtures

Cited by 8 publications

References 8 publications

Kinetics and equilibria of ring closure through an amide linkage. Part 2. 1-Aryl-2-pyrrolidones

Kinetics and equilibria of ring closure through an amide linkage. Part 2. 1-Aryl-2-pyrrolidones

ChemInform Abstract: RELATION OF THE TRANSITION‐STATE STRUCTURE FOR THE WATER‐CATALYZED HYDROLYSIS OF 1‐ACETYLIMIDAZOLIUM ION TO SOLVENT HYDROPHOBICITY: PROTON INVENTORIES IN WATER‐ACETONITRILE MIXTURES

Kinetics of the pH‐independent hydrolyses of 4‐nitrophenyl chloroformate and 4‐nitrophenyl heptafluorobutyrate in water‐acetonitrile mixtures: consequences of solvent composition and ester hydrophobicity

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