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

Abstract

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].

Computational study on vapor phase coupling reaction between diiso(thio)cyanates with diamines, diols, and dithiols

“…E a varies between 100.6 and 175.8 kJ/mol. The calculated energy values are comparable with previous DFT calculations for urea and urethane coupling reactions in the gas phase, confirming the validity of the current calculations of the reaction pathways. It is noted that the reported energies are electronic energies, not enthalpy ( H ) or Gibbs free energy ( G ).…”

Alcohol associates as catalysts of tautomeric transformations

“…This Table 4. Thermodynamic parameters of activation of tautomerization of carbamate VI into azomethinenol VII in gas phase at 298 K: the non-catalytic and catalyzed by the methanol associates Ia-Ic ALCOHOL ASSOCIATES AS CATALYSTS OF TAUTOMERIC TRANSFORMATIONS has been shown for the alcohols reactions with alkyl- [23] and arylisocyanates [24] as well as isocyanic acid [25]; homo associates of phenol [26] and its mixed associates with methanol [27] are more reactive towards isocyanates than the monomeric alcohols; the same effect has been marked in the case of transesterification reactions [28]. The enhancement of reactivity upon association has been revealed for the hydrogen-bond complexes of amines: homo associates of amines [29] and their hetero associates with alcohols [30] are more reactive towards amides formation from esters as compared to the monomeric amines.…”

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

“…The authors calculated and compared energy profiles of the different reaction paths and concluded that auto‐catalytic mechanisms are favored. In a series of studies, Samuilov et al [37,44−51] . investigated reactions of different isocyanates and alcohols based on B3LYP.…”

“…investigated reactions of different isocyanates and alcohols based on B3LYP. The authors compared enthalpies, entropies and free energies of activation for the reaction of the alcohol hydroxy group with the isocyanate C=N and C=O bonds, respectively [37,44−47] . Reactions were considered that proceed via transition states with 4‐rings (see Figures 1 and 2) as well as mechanisms with auto‐catalysis by methanol (Figure 2).…”