Catalytic proton bridge in acetyl imidazolium ion hydrolysis implicated by a proton inventory

Hogg, John L.; Phillips, Mary K.; Jergens, Dana E.

doi:10.1021/jo00434a024

Cited by 14 publications

(10 citation statements)

References 2 publications

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“…These values indicate the extent of development of hydron character of the water molecule that is acting as a general base in the transition state 66. For the reactant state $\phi _{L_i }^{{\rm RS}} $ = 1 and for the full hydron $\phi _{L_i }^{{\rm PS}} $ = 0.69.…”

Section: Resultsmentioning

confidence: 99%

The mechanisms of hydrolysis of N‐alkyl O‐arylthioncarbamate esters

Humeres

Souza

Debacher

2010

J of Physical Organic Chem

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The hydrolysis of N‐ethyl O‐p‐methoxyphenylthioncarbamate (EMeOT) at 50 °C was studied in the range of $H_o^X $ −3.6 to H− 13.7. The pH‐rate profile showed that the hydrolysis occurred through specific acid catalysis at pH <2, spontaneous hydrolysis at pH 2–3, and specific basic catalysis at pH >3. The excess acidity plot against X was linear with slope 0.93, and the Bunnett–Olsen coefficient was 0.07. The acid hydrolysis occurred by an A1 mechanism. The basic hydrolysis of EMeOT can be explained if the mechanism is E1cb. At pH >3 the rate constants increased, reaching a constant value indicating that the expulsion of the aryloxy is not concerted. The neutral species hydrolyzed with general base catalysis with Brønsted β = 0.63 ± 0.07. Water acted as a general base catalyst with (pseudo‐) first‐order rate constant kN = (2.6 ± 0.2) × 10−8 s−1, and inverse kinetic solvent isotope effect of $k_o^D /k_o^H = 2.76$ consistent with a transfer of the proton at a late transition state, as also supported by the highly negative entropy of activation (−31 cal K−1 mol−1). The polynomial expression of the proton inventory curve presented a minimum of the standard deviations that favors the assumption that there are three active protons. The N to O proton transfer to the water molecule forms an incipient hydron. The fractionation factor of the TS of the protons indicated that the hydron is ca. 68% developed at the transition state. Copyright © 2010 John Wiley & Sons, Ltd.

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Section: Resultsmentioning

confidence: 99%

The mechanisms of hydrolysis of N‐alkyl O‐arylthioncarbamate esters

Humeres

Souza

Debacher

2010

J of Physical Organic Chem

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“…In fact, however, it is generally agreed that more than one water molecule is involved. [21] Obviously, the water molecule acting as a nucleophile on the imidazolide carbonyl group is hydrogenbonded to a second water, making the first one more nucleophilic. A further water molecule is expected to be attached by hydrogen bonding to N(3) of the imidazole.…”

Section: In -C-qx X = F Ci Chmentioning

confidence: 99%

Reactivity of Azolides

Staab

Bauer

Schneider

1998

Azolides in Organic Synthesis and Biochemistry

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“…The product could not be distilled but was NMR pure. Due to its hygroscopic nature no satisfactory elemental analysis could be obtained: NMR (CDCla, 35 °C) 3.70 (d, 6 , JPH = 11.25 Hz, P(IV) methoxy H), 3.87 (d, 6 H, JPH = 15.75 Hz, P(V) methoxy H), 7.35 (m, 6 H, aromatic ), 7.80 (m, 4 H, aromatic H); NMR (CD2C12, -80 °C) 3.75 (d, 6 H, JPH = 11.25 Hz, P(IV) methoxy ), 3.90 (d, broadened, JPH = 15.75 Hz, P(V) methoxy H), 7.47 (m, 6 H, aromatic H), 7.85 (m, broadened, 4 H, aromatic H); 81P NMR (CD2C12, -80 °C) -57.7 (d, JPP = 27 Hz, P(V)), -7.7 (d, JPP = 27 Hz, P(IV)).…”

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confidence: 99%

“…Addition of an equivalent amount of acetic acid to a solution of 2,2,2-triethoxy-5-methyl-2,2,3,3-tetrahydro-l,2-oxaphosphole in hexane (~0.1 M solution) resulted in an exothermic reaction with formation of ethyl acetate and the phoephonate. After evaporation of the hexane the residue could be distilled to give pure phosphonate in a nearly quantitative yield: NMR (CDClg, 35 °C) 1.27 (t, 6 H, Jpai = 7 Hz, ethoxy methyl H), ca. 1.90 (m, 2 H, PCH.¡), 2.15 (s, 3 H, CHaCO), ca.…”

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confidence: 99%

“…The pure compound could be isolated by precipitation in ether, followed by thorough washing with ether. The compound was very hygroscopic, and elemental analysis constantly gave low C and N values: NMR (CH2C12, 35 °C) 1.47 (t, 9 H, JHh = 7 Hz, ethoxy methyl H), 2.21 (s, 3 H, CH3CO), 3.30-2.30 (m, 4 H, PCH2CH2), 4.55 (dq, 6 H, Jph = Jhh = 7 Hz, ethoxy ethyl H).…”

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confidence: 99%

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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

Huskey¹,

Hogg²

1981

J. Org. Chem.

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The transition-state structure for the water-catalyzed hydrolysis of 1-acetylimidazolium ion has been probed in solvent systems which may mimic the hydrophobic nature of an enzyme's active site. The kinetic solvent deuterium isotope effects, k^/k^p, are 2.58, 2.49, and 2.10 in water, in 0.5 vol fraction of acetonitrile in water, and in 0.9 vol fraction of acetonitrile in water, respectively. The proton inventory investigations suggest all three solvent systems entertain a transition-state structure composed of a catalytic proton bridge between the reorganizing substrate and a water molecule acting as a general-base catalyst. A "compression" of the transition-state structure in the solvent system containing the largest amount of acetonitrile is suggested to be responsible for the diminished kinetic solvent deuterium isotope effect. The reaction has been shown to be second order with respect to water.

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Catalytic proton bridge in acetyl imidazolium ion hydrolysis implicated by a proton inventory

Cited by 14 publications

References 2 publications

The mechanisms of hydrolysis of N‐alkyl O‐arylthioncarbamate esters

The mechanisms of hydrolysis of N‐alkyl O‐arylthioncarbamate esters

Reactivity of Azolides

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

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