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

Abstract

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.

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

“…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][3][4] investigated reactions of p-nitro-and ----------------*For Communication IV, see [1].…”

“…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.…”

Alcohol associates as catalysts of tautomeric transformations

“…The relative free energy of the process activation was determined by variation of the activation enthalpy. [19,20] as well as of the auto-catalytic addition of alcohols at the C=N bond of isocyanates [21]. In the latter case, carbamate molecules acting as catalyst are transformed into azomethinenols.…”

Catalyzed Reaction of Isocyanates (RNCO) with Water

“…59 Their work highlights many insightful features of a diverse range of RNCO species, but is not connected to any particular reaction mechanisms. In the past decade, a series of studies 45,[60][61][62][63][64][65][66][67] by Konovalov and coworkers predicted the quantum mechanical features of the R 1 NCO + R 2 OH (R 1 , R 2 =Ph, CH 3 , H) reactions in various conditions, including solvent effects and cooperative catalysis with the B3LYP/6-311++G(df,p) method. However, their small sample size precludes a deep understanding of how substituents generally influence the reaction energetics.…”