Hydration of bis(pentamethylphenyl)- and bismesityl-ketenes leading to ene-1,1-diols (enols of carboxylic acids)

Allen, Barbara M.; Hegarty, A. F.; O’Neill, Pat; Nguyen, Minh Tho

doi:10.1039/p29920000927

Cited by 36 publications

(42 citation statements)

References 19 publications

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“…Further, given the structural similarity between the acetic acid and FA carboxyl groups, our results also suggest that in the absence of FA, though the initial mechanism for ketene hydrolysis will involve addition of a water molecule across the carbonyl bond to form the ene−diol, the subsequent production and accumulation of acetic acid as the reaction proceeds will likely alter the preferred pathway to one involving addition of water across the ketene double bond in the later stages of reaction. We note that the reported detection of ene− diol in the aqueous-phase hydrolysis of substituted ketene 28 does not contradict our proposed mechanism, as the observation of the ene−diol in itself does not rule out the possibility of contribution to acetic acid formation also coming from the direct reaction path involving addition of water across the CC double bond with the aid of the organic acid.…”

Section: Discussioncontrasting

confidence: 64%

Hydrolysis of Ketene Catalyzed by Formic Acid: Modification of Reaction Mechanism, Energetics, and Kinetics with Organic Acid Catalysis

et al. 2015

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The hydrolysis of ketene (H2C═C═O) to form acetic acid involving two water molecules and also separately in the presence of one to two water molecules and formic acid (FA) was investigated. Our results show that, while the currently accepted indirect mechanism, involving addition of water across the carbonyl C═O bond of ketene to form an ene-diol followed by tautomerization of the ene-diol to form acetic acid, is the preferred pathway when water alone is present, with formic acid as catalyst, addition of water across the ketene C═C double bond to directly produce acetic acid becomes the kinetically favored pathway for temperatures below 400 K. We find not only that the overall barrier for ketene hydrolysis involving one water molecule and formic acid (H2C2O + H2O + FA) is significantly lower than that involving two water molecules (H2C2O + 2H2O) but also that FA is able to reduce the barrier height for the direct path, involving addition of water across the C═C double bond, so that it is essentially identical with (6.4 kcal/mol) that for the indirect ene-diol formation path involving addition of water across the C═O bond. For the case of ketene hydrolysis involving two water molecules and formic acid (H2C2O + 2H2O + FA), the barrier for the direct addition of water across the C═C double bond is reduced even further and is 2.5 kcal/mol lower relative to the ene-diol path involving addition of water across the C═O bond. In fact, the hydrolysis barrier for the H2C2O + 2H2O + FA reaction through the direct path is sufficiently low (2.5 kcal/mol) for it to be an energetically accessible pathway for acetic acid formation under atmospheric conditions. Given the structural similarity between acetic and formic acid, our results also have potential implications for aqueous-phase chemistry. Thus, in an aqueous environment, even in the absence of formic acid, though the initial mechanism for ketene hydrolysis is expected to involve addition of water across the carbonyl bond as is currently accepted, the production and accumulation of acetic acid will likely alter the preferred pathway to one involving addition of water across the ketene C═C double bond as the reaction proceeds.

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Section: Discussioncontrasting

confidence: 64%

Hydrolysis of Ketene Catalyzed by Formic Acid: Modification of Reaction Mechanism, Energetics, and Kinetics with Organic Acid Catalysis

et al. 2015

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“…As demonstrated in earlier studies, [13][14][15][19][20][21] the attack of water on a double bond is better modelled by, at least, two water molecules that participate fully in the reacting supersystem. In fact, the second water molecule acts as a bifunctional catalyst facilitating the proton transfer.…”

Section: Introductionmentioning

confidence: 85%

“…This is similar to the behavior of ketene regarding protonation and hydration product. 10,11 Nevertheless, it has also been well established both theoretically [11][12][13][14][15] and experimentally [15][16][17][18] that the preferential hydration of ketene 3 is a two-step process involving an addition of water across its C=O bond followed by a conversion of the 1,1-ethenediol intermediate 6 to the more stable acetic acid 7:…”

Section: Introductionmentioning

confidence: 98%

“…15 In some substituted cases, the ethenediol has been detected spectrometrically. 18 On the basis of the fact that the isotope effects are similar in both neutral hydrations of C 3 O 2 and ketene, k(H 2 O)/ k(D 2 O) = 2.2 and 1.6-1.8, respectively, Allen et al 8 suggested that both reactions involve the same mechanism, namely via a diol intermediate.…”

Section: Introductionmentioning

confidence: 99%

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Contrasting mechanism of the hydration of carbon suboxide and ketene. A theoretical study

Nguyen

Raspoet

Vanquickenborne

2000

J. Phys. Org. Chem.

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The protonation and hydration of carbon suboxide (O=C=C=C=O) were studied by ab initio molecular orbital methods. While the geometries of the stationary points were optimized using MP2/6-31G(d,p) calculations, relative energies were estimated using QCISD(T)/6-31G(d,p) and 6-311G(d,p) ZPE. The behaviour of carbon suboxide was compared with that of carbon dioxide and ketene. The protonation at the b-carbon is consistently favoured over that at the oxygen; the proton affinities (PA) are estimated to be PA(C 3 O 2 ) = 775 AE 15 and PA(H 2 CCO) = 820 AE 10 kJ mol À1 (experimental: 817 AE 3 kJ mol À1). The PAs at oxygen amount to 654, 641 and 542 kJ mol À1 (experimental: 548 kJ mol À1 ) for C 3 O 2 , H 2 CCO and CO 2 , respectively. Using the approach of one and two water molecules to model the hydration reaction, the calculated results consistently show that the addition of water across the C=O bond of ketene, giving a 1,1-ethenediol intermediate, is favoured over the C=C addition giving directly a carboxylic acid. A reverse situation occurs in carbon suboxide. In the latter, the energy barrier of the C=C addition is about 31 kJ mol À1 smaller than that of C=O addition. The C=C addition in C 3 O 2 is inherently favoured owing to a smaller energetic cost for the molecular distortion at the transition state, and a higher thermodynamic stability of the acid product. Molecular deformation of carbon suboxide is in fact a fairly facile process. A similar trend was observed for the addition of H 2 , HF and HCl on C 3 O 2 . In all three cases, the C=C addition is favoured, HCl having the lowest energy barrier amongst them. These preferential reaction mechanisms could be rationalized in terms of Fukui functions for both nucleophilic and electrophilic attacks.

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“…The two competitive processes have been studied, both experimentally [36] and theoretically. [37][38][39] In a theoretical study by Skancke, [39] the effect of how the actual number of water molecules participating in the reaction affects the potential energy surface was investigated. He concluded that even though the 1-ketene:1-water potential energy surface is quantitatively different from that of a 1-ketene:2-water surface, similar qualitative conclusion could be drawn: the formation of acetic acid is the thermodynamically favored product, while enediol is slightly favored kinetically.…”

Section: Reactivities Of Ketene Thioketene and Selenoketenementioning

confidence: 99%

A Theoretical Study of the Properties and Reactivities of Ketene, Thioketene, and Selenoketene

Ling¹,

Wong

2000

Eur. J. Org. Chem.

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The properties and reactivities of ketene, thioketene, and selenoketene were studied using the G2(MP2) level of theory. Calculated structures, vibrational frequencies, dipole moments, NMR chemical shifts, and charge distributions strongly suggest that thioketene and selenoketene are best represented by the neutral cumulenic form. Four prototype reactions were examined: ketene‐ynol rearrangement, electrophilic and nucleophilic addition, and [2+2] cycloaddition. Thioketene and selenoketene were found to be more reactive than ketene in all reactions. In terms of chemistry, thioketene resembles selenoketene more than ketene. The variation of reactivity can readily be explained in terms of strain energy, electronegativity, and molecular orbital arguments.

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Hydration of bis(pentamethylphenyl)- and bismesityl-ketenes leading to ene-1,1-diols (enols of carboxylic acids)

Cited by 36 publications

References 19 publications

Hydrolysis of Ketene Catalyzed by Formic Acid: Modification of Reaction Mechanism, Energetics, and Kinetics with Organic Acid Catalysis

Hydrolysis of Ketene Catalyzed by Formic Acid: Modification of Reaction Mechanism, Energetics, and Kinetics with Organic Acid Catalysis

Contrasting mechanism of the hydration of carbon suboxide and ketene. A theoretical study

A Theoretical Study of the Properties and Reactivities of Ketene, Thioketene, and Selenoketene

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