Quantum-chemical study on the reaction of phenyl isocyanate with linear methanol associates: II. Addition at the C=O bond

Samuilov, A. Ya.; Zenitova, L. A.; Samuilov, Ya. D.; Konovalov, A. I.

doi:10.1134/s1070428009010096

Russ J Org Chem

2009

DOI: 10.1134/s1070428009010096

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Quantum-chemical study on the reaction of phenyl isocyanate with linear methanol associates: II. Addition at the C=O bond

A. Ya. Samuilov

L. A. Zenitova

Ya. D. Samuilov

et al.

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Cited by 27 publications

(24 citation statements)

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“…Formerly we carried out a quantum-chemical investigation of the reaction mechanism between phenyl isocyanate with methanol linear associates (monomer, dimer, trimer) [2,3]. It was established that the reactions proceeded through concerted cyclic asymmetric late transition states.…”

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confidence: 99%

Quantum-chemical investigation of isocyanate reactions with linear methanol associates: V. Aryl isocyanate reactions with linear methanol associates

et al. 2012

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The mechanism of addition of linear methanol associates (monomer, dimer, trimer) to aryl isocyanates at their C=N and С=О bonds was investigated applying the quantum-chemical method B3LYP/6-311++G(df,p). Notwithstanding the electronic character of substituents in the aromatic ring of the isocyanates all reactions proceed through concerted asymmetric late transition states. The addition to the C=N bond is considerably more preferable than to the С=О bond. In the transformations under consideration the intermolecular donor-acceptor interactions between the reagents result in the appearance of abnormal selectivity.Formerly we carried out a quantum-chemical investigation of the reaction mechanism between phenyl isocyanate with methanol linear associates (monomer, dimer, trimer) [2, 3]. It was established that the reactions proceeded through concerted cyclic asymmetric late transition states. With the growing degree of the alcohol association the activation barriers on the conversion route decrease due to the growing electron-donor property of the alcohol, and increases the thermodynamic feasibility of their reaction with isocyanates [1,4].In order to reveal whether the mechanism of the alcohol reaction with isocyanates might change with the change of the electronic character of substituents in the isocyanates we supplementary to the previously obtained data [2-4] investigated reactions of p-nitro-and ----------------*For Communication IV, see [1].p-methoxyphenyl isocyanate with the methanol linear associates.The electronic character of the substituents in the aryl isocyanates in question is essentially different. It was therefore expectable that if the substituents in the aromatic ring of isocyanates might cause a change in the reaction mechanism, it would be observed in the reactions under study.Quantum-chemical calculations were performed by the method B3LYP/6-311++G(df,p) employing the package of the applied programs GAUSSIAN 03 [5,6]. The preliminary geometry optimization was carried out by the density functional method with the help of PRIRODA 6 program [7] using the basic L11 (analog of cc-pCVDZ [8]). The search for the transition state was fulfi lled with respect to the fi rst negative oscillation frequency in the Hesse matrix. The verity of the transition state was determined by the procedure of the decent from the transition state point in two directions using the IRC procedure with the subsequent geometry optimization of the obtained prereaction and postreaction complexes. The principles of the estimation of conformer structures corresponding to the minimal energy are described in [2].

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Quantum-chemical investigation of isocyanate reactions with linear methanol associates: V. Aryl isocyanate reactions with linear methanol associates

et al. 2012

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“…In the course of the reaction prereaction and postreaction complexes arise formed involving hydrogen bonds [1,6,7]. The reactions with alcohol associates are more favorable not only kinetically, but also thermodynamically [1,[6][7][8].…”

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confidence: 97%

“…In this report we discuss the addition of complexes IIIa, IIIb to the C=N bond of isocyanate IV. We have shown previously that the addition of the linear associates of methanol to the C=O bond of phenyl isocyanate [7], methyl isocyanate [1] should overcome much higher activation barriers than those in the reactions at the C=N bond. The reason of this phenomenon is the fact, that the rupture of the C=O bond in the transition state requires much more energy expenditure than the breaking of the C=N bond.…”

mentioning

confidence: 98%

“…The mechanism of the reaction between isocyanates and alcohols was elucidated by quantum-chemical calculations [1,[6][7][8]. It turned out that the transformations under discussion occurred through late concerted asymmetric transition states where the degree of the formation of the new carbon-oxygen bond outraced the extent of the formation of another bond.…”

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confidence: 99%

“…We calculated for discussed transition states VIa, VIb The parameter f (Table 2), which quantitatively (in percent) characterized the extent of formation of new and of cleavage of old bonds. The principles of calculating parameter f are presented in [1,6,7].…”

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confidence: 99%

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Quantum-chemical investigation of isocyanate reactions with linear methanol associates: IV. Mechanism of autocatalytic reaction of methyl isocyanate with linear methanol associates

et al. 2012

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It was shown by quantum-chemical method B3LYP/6-311++G(df,p) that in the autocatalytic reaction the molecules of methyl carbamate formed prereaction complexes with the monomer and dimer of methanol. The complexes possess higher electron-donor properties than free alcohol molecules thus increasing the activity of complexes in the reaction with isocyanates. The products of the autocatalytic reaction are new molecules of carbamate and azomethinenol. The conversions occur through concerted asymmetric late transition states. The isomerization of azomethinenols into carbamates is catalyzed by molecules of alcohols and their associates. The autocatalytic reaction of isocyanates with alcohols becomes possible owing to the ability of alcohols to catalyze the mentioned isomerization.

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Reaction Mechanisms and Rate Constants of Auto‐Catalytic Urethane Formation and Cleavage Reactions

et al. 2021

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The chemistry of urethanes plays a key role in important industrial processes. Although catalysts are often used, the study of the reactions without added catalysts provides the basis for a deeper understanding. For the non‐catalytic urethane formation and cleavage reactions, the dominating reaction mechanism has long been debated. To our knowledge, the reaction kinetics have not been predicted quantitatively so far. Therefore, we report a new computational study of urethane formation and cleavage reactions. To analyze various potential reaction mechanisms and to predict the reaction rate constants quantum chemistry and transition state theory were employed. For validation, experimental data from literature and from own experiments were used. Quantitative agreement of experiments and predictions could be demonstrated. The calculations confirm earlier assumptions that urethane formation reactions proceed via mechanisms where alcohol molecules act as auto‐catalysts. Our results show that it is essential to consider several transition states corresponding to different reaction orders to enable agreement with experimental observations. Urethane cleavage seems to be catalyzed by an isourethane, leading to an observed 2nd‐order dependence of the reaction rate on the urethane concentration. The results of our study support a deeper understanding of the reactions as well as a better description of reaction kinetics and will therefore help in catalyst development and process optimization.

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Quantum-chemical study on the reaction of phenyl isocyanate with linear methanol associates: II. Addition at the C=O bond

Cited by 27 publications

References 3 publications

Quantum-chemical investigation of isocyanate reactions with linear methanol associates: V. Aryl isocyanate reactions with linear methanol associates

Quantum-chemical investigation of isocyanate reactions with linear methanol associates: V. Aryl isocyanate reactions with linear methanol associates

Quantum-chemical investigation of isocyanate reactions with linear methanol associates: IV. Mechanism of autocatalytic reaction of methyl isocyanate with linear methanol associates

Reaction Mechanisms and Rate Constants of Auto‐Catalytic Urethane Formation and Cleavage Reactions

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